|
|
| 1. |
Computer simulation of electrochemical processes on interfaces |
| |
Russian Chemical Reviews,
Volume 67,
Issue 2,
1998,
Page 93-108
Gennadii V. Khaldeev,
Preview
|
|
ISSN:0036-021X
出版商:RSC
年代:1998
数据来源: RSC
|
| 2. |
Chemistry of semiconductor nanoparticles |
| |
Russian Chemical Reviews,
Volume 67,
Issue 2,
1998,
Page 109-122
Rafail F. Khairutdinov,
Preview
|
|
ISSN:0036-021X
出版商:RSC
年代:1998
数据来源: RSC
|
| 3. |
Excited state proton transfer dye lasers |
| |
Russian Chemical Reviews,
Volume 67,
Issue 2,
1998,
Page 123-136
Boris M. Uzhinov,
Preview
|
|
摘要:
Abstract. Reactions of proton phototransfer in organic com- pounds and photochemical lasers based on these reactions are considered. A principle of operation of a photochemical laser is described. Selection criteria of acid-base systems to serve as active media in photochemical lasers are determined. A list of acid-base laser systems, conditions of their fabrication, and emission characteristics are collated.Specific losses in photochemical lasers are analysed. Methods of expanding the spectral range of tunable emission in the photochemical lasers are described. The bibliography includes 134 references. I. Introduction Laser radiation is the emission of light upon transition of excited molecules to the ground electronic state. The emission of light is stimulated by an external electromagnetic field under the con- ditions of an optical resonator. The phenomenon of light ampli- fication by the effect of stimulated radiation emission is called laser action, which stems from the abbreviation of the expression `light amplification by stimulated emission of radiation'.Among numerous types of lasers used in the different fields of science and technology, those based on organic compounds (dyes) occupy a special place.1 The advantages of the dye lasers over the others include the possibility of fine and continuous tuning of the laser radiation wavelength over a wide range (up to 100 nm), a high coefficient of emitted light amplification by the active medium, and the possibility of obtaining multiband radiation.2 The latter is employed for the solution of a number of practically important problems (in particular, atmospheric probing, multipulse multi- colour spectroscopy, etc.).Dye lasers are the main source of pico- and femtosecond pulses.3 The possibility of achieving the femto- second pulses is determined by the existence of highly effective amplification medium with a broad range of laser radiation tuning.A significant increase in the spectral range of tuning, up to 220 nm,4 can be attained in the dye lasers with adiabatic photochemical reactions. A dye produces stimulated light emission in the spectral range of its fluorescence. The excited dye molecules may be generated in two ways: (1) as a result of direct excitation from the ground state through absorption of a photon or under electron impact; (2) as a result of an adiabatic photochemical reaction (photochemical laser).The regularities of radiation for the first type of dye laser are considered in numerous reviews and original papers.5± 11 The reactions of electron and proton phototransfer belong to the best studied adiabatic photochemical reactions of organic com- pounds.12 The electron phototransfer reactions result in the formation of excited charge-transfer complexes (exciplexes).13 The radiative transition in exciplexes is partially forbidden, there- fore, the generation of laser radiation by the products of electron phototransfer reactions and, consequently, photochemical lasers based on these reactions are hardly probable.14 The radiative transition in excited products of numerous proton phototransfer reactions is permitted.15 These excited products are the potential generators of the laser radiation.II. An operation scheme for a photochemical laser based on proton phototransfer reactions Proton phototransfer reactions in organic compounds occur according to static and dynamic mechanisms. In the former case the reaction occurs `instantaneously' in the excitation of a hydro- gen-bonded complex of a proton donor with acceptor, which is formed in the ground state. In the latter case, the interaction between the excited molecule of an aromatic compound and a molecule of a base or acid is realised.Fluorophores that can participate in the acid-base interaction may be divided into two groups. Proton-donor fluo- rophores ArXH constitute the first group, their acidity being increased upon excitation.A reaction with a base B in the ground state occurs according to the scheme The majority of compounds of this group possess an aromatic radical Ar bound by a single bond to the proton-donor group XH (X=O, S, NR, and NRá2 ).16 ± 19 The kinetic and thermodynamic parameters of reaction (2) and spectral-kinetic characteristics of the forms ArXH and ArX7 for the known laser acid-base systems are listed in Table 1.(A H... B) (A H... B)* (A7 H B+)* . ... (1) (2) ArXH*+B ArXH7*+B+, (3) ArXH* ArXH7 * B ... B+. ... BMUzhinov, S I Druzhinin MV Lomonosov Moscow State University, Department of Chemistry, Leninskie gory, 119899 Moscow, Russian Federation. Fax (7-095) 932 88 46. Tel.(7-095) 939 26 85 (BMUzhinov). E-mail: drush@comp.chem.msu.su Received 5 November 1997 Uspekhi Khimii 67 (2) 140 ± 154 (1998); translated by LMGoldenberg UDC 621.375.9:535 +541.14 Excited state proton transfer dye lasers BMUzhinov, S I Druzhinin Contents I. Introduction 123 II. An operation scheme for a photochemical laser based on proton phototransfer reactions 123 III. Selection criteria of acid-base systems for active media in photochemical lasers 128 IV. Acid-base laser systems 129 V.Losses in photochemical lasers 131 VI. Tunable photochemical lasers 133 Russian Chemical Reviews 67 (2) 123 ± 136 (1998) #1998 Russian Academy of Sciences and Turpion LtdAH* +H2O A7*+H3O+ k Table 1. The spectral-luminescence characteristics of conjugated acid-base forms of dyes for photochemical lasers and the parameters of the intermolecular proton phototransfer reactions Laser dye AH, la e lf jf t k pK a ± pKa Ref.A7 /nm /mol71 litre cm71 /nm (%) /ns /mol71 litre ns71 2-Naphthol AH 327 a 3.08 a 357 a 40 b 7.9 0.075 c 2.78 d 17 A7 345 a 1.78 a 418 a 57 b 9.0 46 76.79 17 Potassium 7-hydroxy- AH 337 1.69 e 385 ± 10.5 >5 c 0.76 d 23 naphthalene-1,3-disulfonate AH ± ± 388 ± 14.5 3.8 c 0.60 d 24 A7 359 3.38 e 470 ± 15.5 <200 78.34 23 A7 389 ± 458 ± 26.2 16 77.29 24 Sodium 8-hydroxypyrene-1,3,6- AH 402 f 19.2 f 441 ± 5.2 8.0 c 1.28 d 26 trisulfonate AH ± ± ± 70 4.8 6.1 c 0.95 d 27 A7 453 f 18.2 f 510 85 5.3 115 ± 26 A7 ± ± ± 85 6.0 55 76.45 27 Sodium 8-acetylaminopyrene- AH 371 28 443 ± 4.0 1.48 6.9 d 19 1,3,6-trisulfonate g A7 408 20 553 85 5.0 2.161079 c 77 19 1,3-Disulfo-7-naphthylammonium AH 281 5.55 345 ± 15 20 c <74.7 d 22 hydrogensulfate A7 350 3.96 450 84 14.7 <1074 <77.6 22 Note.Here and in Tables 2 and 3, the following designations are used: la is the absorption spectrum maximum, lf is the fluorescence spectrum maximum, e is the extinction coefficient for the absorption spectrum maximum, jf is the fluorescence quantum yield, t is the fluorescence lifetime.a From Ref. 20. b From Ref. 21.c Rate constant for a unimolecular tautomerisation reaction or a quasi-unimolecular reaction with the solvent (s71). d pK a . e From Ref. 22. f From Ref. 25. g Reaction (2) with the OH7 ion. Table 2. Spectral-luminescence characteristics of conjugated acid-base forms of dyes for the photochemical lasers and the parameters of proton intermolecular phototransfer reactions (4) in ethanol.Laser dye AH, la e lf jf t Reagent k pK a ± pKa Ref. A7 /nm /mol71 litre cm71 /nm (%) /ns /mol71 litre ns71 N-Phenylacridone B 399 ± 406 100 12 H3O+ 7.4 a 2.05 b 33 BH+ 427 ± 450 ± ± 2.92 33 3-Methoxybenzanthrone B 445 24.3 c 547 57 7.8 H3O+ 6.4 a 2.2 b 33 BH+ 585 ± 640 28 3.8 5.85 33 2,3,6,7-Tetrahydro-1H,5H- B 389 d 21.5 d 470 95 4.52 EtOHá2 4.33 35 benzopyrano[6,7,8-ij]quino- BH+ ± 533 40 ± 5.51 e 35 lizin-11-one 9-Methyl-2,3,6,7-tetra- B 396 d 25.0 d 470 83 4.36 EtOHá2 3.56 35 hydro-1H,5H-benzopyrano- BH+ ± ± 530 47 5.45 f 5.14 e 35 [6,7,8-ij]quinolizin-11-one 5H-9-Diethylamino-5-imino- B 510 ± 605 ± 1.85 EtOH 0.04 g 3 38 benzo[a]phenoxazine BH+ 625 ± 660 h 22 i 1.3 h 1.5 j 38 BH+ 633 77.5 672 ± ± 34 5-Phenyl-2-(4-pyridyl)- B 322 k 24.5 k 400 k 46 2.12 AcOH 0.314 8.27 l 30 oxazole BH+ 370 k 24.5 k 475 k 59 8.44 e 30 5-(4-Methoxyphenyl)-2- B 335 k 21.5 k 447 k 91 2.45 AcOH 0.501 8.78 l 30 (4-pyridyl)oxazole BH+ 399 k 21.0 k 550 k 64 3.08 10.04 e 30 5-Phenyl-2- B 350 k 21.5 k 423 k 61 1.89 AcOH 0.175 8.85 l 30 (2-quinolyl)oxazole BH+ 412 k 18.5 k 515 k 73 3.66 9.01 e 30 5-Phenyl-2-(4-quinolyl)- B 350 k 18.5 k 437 k 63 1.87 AcOH 0.263 8.04 l 30 oxazole BH+ 412 k 23.9 k 525 k 45 2.18 9.01 e 30 1,4-Bis(5-phenyloxazol- B 360 47.2 m 420 93 m 1.4 m CF3COOH ± 42 2-yl)benzene n BH+ ± ± 486 ± ± 6.78 l 42 1,4-Bis[5-(4 0-methylphenyl)- B 362 51.1 m 430 93 m 1.5 m CF3COOH ± 42 oxazol-2-yl]benzene n BH+ ± ± 500 ± ± 6.83 l 42 a k1/(1+k± 1t00) from Ref. 32. b pK a . c From Ref. 32. d From Ref. 34. e According to the FoÈ rster cycle 36 using the absorption spectra. f From Ref. 37. g Rate constant for a unimolecular tautomerisation reaction or a quasi-unimolecular reaction with the solvent (ns71). h Ion pair. i From Ref. 39. j pK for an equilibrium ion pair ± complex with H-bond. k From Ref. 40.l According to the FoÈ rster cycle 36 using the fluorescence spectra. m In cyclohexane.41 n In dioxane, reaction (5). 124 BM Uzhinov, S I DruzhininProton-acceptor fluorophores constitute the second group, their basicity is increased upon excitation In this type of base, the p-system is linked by a double bound to the proton-acceptor centre. The proton-acceptor centre can be exocyclic or endocyclic.Aromatic carbonyl compounds (aldehydes and ketones) and their imine derivatives belong to the organic bases with an exocyclic proton-acceptor centre. Organic carbonyl compounds are weak bases.28 Their basicity is increased in the excited state.29 The protonation rate constants for aminocoumarins in the excited state in solution are close to the diffusion rates.29 The rate constants for the protonation of pyridine and oxazole derivatives in the excited state by carboxylic acids are one or two orders of magnitude smaller than the rate constants for the diffusion- limited reactions, respectively.30, 31 The photoprotonation of pyridine and oxazole derivatives occurs either according to the static [reaction (5)] or dynamic [reaction (4)] mechanism.30, 31 The kinetic and thermodynamic parameters for the reactions (4) and (5) and spectral-kinetic characteristic of the forms B and BH+ for the known laser acid-base systems are listed in Table 2.Aromatic C-bases possess low basicity. These compounds are protonated in the ground state only in concentrated strong acids. The acid-base interaction in the excited state leads to quenching of the fluorescence.No excited products are generated in this reaction.43, 44 In numerous organic compounds, the proton-donor and proton-acceptor groups are linked by an intramolecular hydrogen bond.45 ± 48 The proton-donor and proton-acceptor ability of these reaction centres of the molecule is increased upon excitation of these compounds, which results in the intramolecular proton phototransfer.This type of reaction can be assigned to the stationary proton phototransfer. The kinetic and thermodynamic parameters for the reactions of intramolecular proton photo- transfer as well as spectral-kinetic characteristics for the known laser systems of this type are listed in Table 3. (5) HA B ... BH+ * ... A7. (4) B+HA BH+ *+A7, Table 3. Parameters of reactions of intramolecular proton phototransfer in dye molecules for photochemical lasers and spectral-luminescence characteristics of the initial form (N) and its tautomer (T).Laser dye Form Solvent la e lf jf t pK a ± pKa Ref. /nm /mol71 litre cm71 /nm (%) /ns Sodium salicylate N EtOH 298 4.2 ± ± ± ± 41 T 405 27 26 a 41 Salicylamide N DMF 305 ± ± ± ± ± 49 T 438 27 2.6 49 3-Hydroxyflavone Nb MeOH 344 16.35 405 ± 1.24 79.61 c 51 ± 4.08 d 51 T 531 ± 2.34 712.3 e 51 Nf Methyl- ± 25 h 410 ± ± ± 50 Tg cyclohexane 526 36 3 53 2,20-Bipyridyl-3,30-diol Ni 3-Methyl- 360 j 17.5 j ± <0.01 6.6 a ± 55 T pentane 513 31 3.2 54 2-(Benzimidazol-2-yl)phenol N Dioxane 333 28.0 k 350 ± ± 715.1 e 57 T 468 65 4.2 57 N MeCN 331 22.1 k 354 713.9 e 57 T 463 55 3.7 57 N DMF 333 27.5 k 354 30 1.4 713.9 e 57 T 463 72 4.1 57 N MeOH 329 28.0 k 351 37 1.5 78.0 e 57 T 405 57 3.8 57 2-(Benzimidazol-2-yl)- N Dioxane 339 22.8 k 352 5 1.5 716.7 e 57 4-methylphenol T 489 65 4.5 57 2-(Benzimidazol-2-yl)- N MeCN 339 24.1 k 359 ± ± 714.5 e 57 4-fluorophenol T 478 73 4.7 57 2-(Benzimidazol-2-yl)- N Dioxane 341 20.2 k 368 7 1.9 717.4 e 57 4-methoxyphenol T 530 48 4.2 57 2,5-Bis(benzimidazol-2-yl)- N " 345 34.0 k 358 6 2.0 718.6 e 57 hydroquinone T 525 39 3.4 l 57 N MeCN 342 19.6 k 369 6 1.8 716.3 e 57 T 517 18 3.4 57 N DMF 347 22.0 k 381 8 1.8 715.1 e 57 T 525 21 2.6 57 3,6-Bis(benzoxazol-2-yl)- Nm MeTHF 381 24.7 445 n 35 ± 78.9 e 59 4-methoxyphenol T 548 50 4.6 59 N-[2-(5-Phenyl-1,3,4-oxadiazol- N EtOH 312 12.5 330 ± ± 722.4 e 60 2-yl)phenyl]toluene-p-sulfamide T 510 3 0.90 60 a Radiative lifetime of fluorescence.b Rate constant of proton phototransfer (k) >8000 ns71 (Ref. 50). c Deprotonation. d Protonation. e According to the FoÈ rster cycle 36 using the fluorescence spectra. f k=4200 ns71. g k=30 ns71 in cyclohexane.52 h In cyclohexane.52 i k >7000 ns71. j From Ref. 54. k From Ref. 56. k From Ref. 58.m k=20 ns71. n For 1,4-dimethoxy-2,5-bis(benzoxazol-2-yl)benzene. Excited state proton transfer dye lasers 125Intramolecular proton phototransfer reactions leading to species with effective fluorescence are wide-spread (see Tables 1 and 2). Compounds that give products with a high quantum yield of fluorescence of the intramolecular proton phototransfer prod- uct are scarce.59, 61 ¡¾ 64 The fluorescent reaction products of the proton phototransfer, as with usual fluorophores, under appro- priate conditions can amplify the light passing through the solution.In a number of studies that were performed over the period from 1960 to 1964, the possibility of the light amplification by the dye solutions has been demonstrated,65 and the principles of generation of laser radiation (lasing) as a result of electron- vibrational singlet ¡¾ singlet transitions in anthraquinone molecule have been discussed.66 Certain theoretical calculations on lasing taking into account the vibrational structure of the electronic levels of dyes were carried out.67, 68 The processes that occur in the excitation of complex molecules, including the processes of stimulated light emission, were analysed in detail.69, 70 Slight amplification of light upon photoirradiation of a solution of perylene in benzene was detected in 1964.71 The lasing of organic compounds was first observed inde- pendently by two research groups.72, 73 Chronologically, the first dye laser was created by Sorokin and Lankard 73 in 1966.Excitation of an ethanolic solution of phthalocyanine complex with aluminium chloride by the radiation of a ruby laser induced laser radiation resulting from electronic transitions in the organic ligand of the metallocomplex.Currently, dye lasing with a high conversion efficiency (71% for the Rhodamine 6G in EtOH 75 and 78% for the dye LKK-756 in MeCN76) can be obtained in a spectral range from 322 nm74 to 1800 nm.10 Arylazole, coumarin, xanthene, oxazine, and polymethine dyes are the most efficient laser dyes.7 Active media for the dye lasers are liquid solutions of dyes,1, 5 solid solutions in polymers,77 and gaseous mixtures of dye vapour with buffer gases.78 A solution of an organic compound can generate laser radiation (lase) if its optical density [7ka(n)x] at some frequency n is less than zero (negative absorption).79 lnI0OnU IOnU a ¢§kaOnUx, where I0 (n) and I(n) are the radiation flux intensities before and after the light has passed through the layer of a solution with a thickness x, ka(n) is an amplification coefficient of the medium.In the simplest case of a two-level scheme, ka(n) is described by the equation kaOnU a hn u N2B21OnU ¢§ N1B12OnU, where N1 and N2 are the population of the lower (1) and upper (2) levels, B12(n) and B21(n) are the probabilities of absorption and stimulated emission (Einstein's coefficients for induced transi- tions), respectively, u is the velocity of light in the medium.More often, a cross-section of stimulated transition is used instead of B(n) sOnU a hn u BOnU . The Einstein coefficients, cross-sections of absorption and stimulated emission are the same, i.e., B12OnU a B21OnU and s21OnU a s12OnU.The condition for lasing kaOnU a N2s21OnU ¢§ N1s12OnU a s21OnUON2 ¢§ N1U > 0 is fulfilled whenN2>N1 , i.e., in the presence in the system with an inverted (relative to thermal population) level population. This cannot be achieved in the two-level system with optical pumping.The currently known laser systems lase according to three- (1 ¡¾ 3) and four-level (1 ¡¾ 4) schemes (Fig. 1). Optical transitions occur between the levels 1 ¡¾ 2 and 3 ¡¾ 4. The system is excited from the lower vibrational sublevel of the main electronic state (level 1) to higher vibrational sublevels of the first excited electronic state (level 2). The lower laser level (level 4) consists of higher vibra- tional sublevels of the ground electronic state of the dye, the upper laser level (level 3) is a zero vibrational sublevel of the first excited electronic state.The transitions between the levels 2 ¡¾ 3 and 4 ¡¾ 1 are radiationless (the rate constant of these processes is *103 ns71). They represent vibrational relaxation in the excited and ground electronic states, respectively. As the higher vibrational sublevels of the ground state are virtually unoccupied at room temperature, the concentration of excited molecules at the level 3 (N3) exceeds that of molecules at the level 4 (N4) upon excitation of the system even by light of relatively low power.In this case, an inverted population of the levels 3 and 4 is observed in the system (N3 > N4).An inverted population of the zero vibrational sublevels of the ground and excited states cannot be achieved. In addition to these processes, optical transitions from the level 3 to the highest singlet states of the molecule (level 5), intersystem transitions to the triplet state (level 6) and optical transitions from the level 6 to the highest triplet level of the molecule (level 7) as well as photochemical decay of the dye occur in the dye lasers.For the system that is described by this scheme the amplification coef- ficient is determined by the equation kaOnU a N2as34OnU ¢§ s35OnUa ¢§ N1s12OnU ¢§ N6s67OnU¢§ (6) ¢§Xi Npispi OnU ¢§ kwOnU, where the number in subscript indicates the number of the level, Npi is the population of levels, spi (n) is the cross-section of absorption of photoproduct pi at a frequency n, kw(n) is the constant loss coefficient.Spectral criteria for the selection of a dye to produce efficient lasing have been formulated by Simo- nov 80 and Denisov and Uzhinov 81. The idea of creating an inverted electronic state population as a result of the adiabatic reaction of organic compounds in excited state was suggested practically simultaneously by Derkacheva 82 and Kuz'min 83 (3 years before the appearance of the first dye laser 73).It was assumed that photochemical reactions of dissoci- ation, isomerisation, complexation, dimerisation, and polymer- isation and redox processes can be adiabatic.83 In the four-level scheme suggested,82, 83 the ground and excited states of the initial form of the dye involved in the reaction correspond to levels 1 and 2 (see Fig. 1). The excited and ground state of the proton photo- transfer product correspond to levels 3 and 4. In this case, the direct reaction in the excited state and the reverse reaction in the ground state play the roles of radiationless relaxation processes (transitions between the levels 2 ¡¾ 3 and 4 ¡¾ 1), respectively.The change in the equilibrium constant in the excited state compared to the ground state is crucial for lasing. Derkacheva 82 has considered the mechanism of lasing of products of photoprotolytic reactions of phenols in water, which occur according to the following scheme. 2{ 5{ }7 3 6 }4 1 Figure 1. The energy level diagram of a laser dye molecule. 126 BM Uzhinov, S I DruzhininThe value k¢§1 34 is the lifetime of the excited product of the photoreaction.It was considered 82, 83 that the attainment of an inverted population between the zero vibrational sublevels of the excited and the ground states of RO7 is a prerequisite for lasing. The difference in populations of these states under steady-state conditions is determined by the equation 82 aRO¢§a ¢§ aRO¢§a a aROHah ak23=k34 1 a k32aH3Oaa=k34 1 ¢§ 1 k41aH3Oaa=k34 ¢§ k14 k41aH3Oaai, where a=[ROH*]/[ROH].The following two conditions should be fulfilled to ensure an inverted population in the reaction product ([RO7*]>[RO7]): (1) [H3O+] > k34/k41; (2) sufficiently intense excitation, which determines the value of a, as well as large value of k23, which provides for the high formation rate of the excited molecules of the deprotonated form.In the case of acid dissociation of the excited 2-naphthol, the first condition is fulfilled at pH<1.7 ([H3O+]> 0.02 mol litre71), and the second condition if sufficiently power- ful excitation sources are employed.82 More recent studies have shown that the mechanism of lasing suggested earlier 82, 83 is invalid.Currently, it is believed that an inverted population between the zero vibrational sublevels of the excited state and the vibrational sublevels (excluding zero sub- level) of the dye ground state is the prerequisite for lasing in organic compounds.79 This is also a prerequisite for the radiation of a photochemical laser. However, in this case the inverted population can also occur between the zero vibrational sublevels of the excited and ground states of the lasing species.Due to spectral overlap of the stimulated emission of the components, the initial form influences significantly the emission by the photochemical reaction product, and vice versa the product influences the emission by the initial form.Thus, the properties of both components of an acid-base system determine the radiation characteristics of the photochemical laser. The energy diagram of the photochemical laser is a combination of 7-level schemes for the initial compound and the photoreaction product. In a general case, the diagram contains 14 levels (Fig. 2). The amplification coefficient of the active medium in such a laser is determined by the equation 22 kaOnU a N3as31OnU ¢§ s35OnUa ¢§ N1s12OnU ¢§ N6s67OnUa (7) +N30 as3010 OnU ¢§ s3050 OnUa ¢§ N10s1020 OnU¢§ ¡¾N60s6070 OnU ¢§Xi Npispi OnU ¢§ kwOnU, where the quantities corresponding to the photoreaction product are primed.Analysis of the features of laser radiation of a system with an intermolecular proton transfer reaction at steady-state excita- tion 84 shows that the system is described by two pairs of electronic-vibrational levels for the initial form (1, 2) and the photoreaction product (10, 20), respectively; the transitions to the triplet levels are absent and the concentration of the reaction product in the ground state N10 is taken to be equal to zero.84 When the intensity of excitation (Ie) is higher than the threshold for the photoreaction product (I 0t) and lower than the threshold for the initial form (It) and the laser radiation is generated only by the photoreaction product at a frequency n 0, its radiation power is increased with the intensity of excitation up to the maximum value I 0max at Ie=It.On further increase in Ie , the passage of the system into a two-band generation mode occurs with frequencies n 0 and n: I 0On0U a I 0maxOn0U ¢§ s2010 OnU s2010 On0U IOnU, IOnU a COIe ¢§ ItU, I 0max a s12OnUON ¢§ kwOn0U=s2010 On0UU a kwOnU kwOn0Us21OnUa1 a expOhOn0 ¢§ n000U=kT a Ok220 ¢§ kmin 220 U, kmin 220 a kwOn0Us21OnUk2010 s2010 On0U , where C is a coefficient,Nis an analytical dye concentration, n 000 is the frequency of the 0 ¡¾ 0-transition in the reaction product, kmin 22 0 is a minimum rate of the proton transfer reaction in the excited state, which provides the appearance of lasing of the product.The coefficient c is independent of pump power. If fluorescence spectra of the initial form and the reaction product do not overlap at the frequencies of lasing n and n 0 [s21(n0)=s2010 (n)=0], then the laser radiation power for the photoreaction product is independent of Ie if Ie 5 It.It was concluded 84 that I 0max is proportional to the rate constant for the proton transfer reaction in the excited state. If fluorescence spectra of the initial form and the product overlap at the frequency of lasing of the initial form [s21On 0U=0, s2010 (n)>0], then participation of the reaction product in the lasing of the initial form leads to an increase in amplification at the frequency of its lasing.For Ie5It , this leads to the situation, where the power of laser radiation at the frequency n increases faster than in the previous case, but at the frequency n 0 the power drops until the ceasing of generation at IOnU a I 0maxOn0Us2010 On0U s2010 OnU . In other words, two thresholds (upper and lower) in the lasing of the photoreaction product should be observed for such a system.The range of Ie, where two-band laser radiation exists, is the wider the smaller s2010 (n) and the larger k220 . Analysis of changes in the generated power of laser radiation at frequencies n and n 0 provided N10 > 0 has shown 84 that at Ie>It and s21(n 0)=s2010 OnU a 0 the generation threshold at the frequency n depends on the acidity of the medium due to absorption of the excitation radiation by the photoreaction product N10s1020 OnpUIp .A limiting value for the ratio of the rate constants for the direct reaction in the excited state and the reverse reaction in the ground state exists k220 k101 a a s1020 OnU , where coefficient a is independent of Ie.If this ratio is greater than the limiting value, the generation threshold for laser radiation of initial form becomes infinitely large. Neglecting the terms that correspond to the absorption of light by the products of irreversible reactions of photodecay and constant losses in the resonator, Kasha and co-workers 53, 85 ¡¾ 87 derived an expression similar to (7) for the change in the ROH* +H2O ROH+H2O RO7*+H3O+ RO7+H3O+.k23 k32 k34 k14 k41 3 6 1 30 60 10 7 5 2 4 20 50 70 40 Figure 2. The energy level diagram of the components of a photo- chemical laser. Excited state proton transfer dye lasers 127amplification coefficient of a photochemical laser based on the reaction of intramolecular proton phototransfer of 3-hydroxy- flavone in methylcyclohexane.In the approximation of a fast proton transfer reaction in the excited (k¡¦1 303< 8 ps) and ground states and neglecting the induced absorption Sn S1 [s35(n)=0], Tn T1 [s67(n)=0], Sn0 S10 [s3050 (n)=0], and Tn0 T10 [s6 070 (n)=0], they obtained an amplification coefficient of the active medium equal to 10 cm71 at an excitation power of 500 kW (l=337 nm) and dye concentration of 1.64 mmol litre71 (Ref. 53). Radiation kinetics of a photochemical laser based on a binary mixture of dyes, 2-(biphenyl-4-yl)-6-phenylbenzoxazole and 2-(2- hydroxyphenyl)benzoxazole, was studied 58, 88 in the generation band of the first dye and a bifluorophore comprising these two dyes bound chemically. The solution of a direct kinetic problem to describe the radiation kinetics was attempted.88 Using literature data on the optical properties of dyes, and experimental character- istics of the exciting radiation (308 nm) and optical resonator, and neglecting the light absorption by the singlet- and triplet-excited molecules, it was concluded 88 that the laser pulse duration of the first dye should be much smaller in the presence of the second dye.The results of calculation were in agreement with experiment.The laser pulse duration was 3.3 ns in the absence of the second dye and 80 ps in the presence of the second dye. It was assumed in the calculation 88 that the induced absorption in this system corre- sponds to absorption of a tautomer of the second dye in the ground state [s1020 (n) > 0]. However, the induced absorption in 2-(2-hydroxyphenyl)benzoxazole was later assigned to Tn/T1 absorption of the dye [s67 (n)].89, 90 The dynamics of lasing of the product of the intramolecular proton transfer in salicylamide and derivatives of 2-(2-hydroxy- phenyl)benzoxazole in DMF48 was described by the system of differential equations based on a previously employed model.53, 85 ¡À 88 It was assumed in the calculation that the rate constants for the direct proton transfer in singlet excited state of initial form (k220 ) and reverse proton transfer in triplet excited state (k606) are equal to 1012 and 109 s71, respectively.Absorption by the excited singlet state [s35(n)=s3050 (n)=0] was neglected. The values calculated s1020 (n)=8.0610719 ¡À 2.3610717 cm2 cor- relate linearly with a cross-section of stimulated emission of the tautomer at a frequency of the spectral maximum of lasing (this was estimated from the fluorescence spectrum).It was con- cluded 58 that the rate of reverse proton transfer in the ground state (k101=1.506108 s71) and light absorption by the reaction product in the ground state are the main factors determining lasing of the product of intramolecular proton phototransfer of 2-(2-hydroxyphenyl)benzoxazoles and salicylamide.III. Selection criteria of acid-base systems for active media in photochemical lasers The cross-section of stimulated emission (s34) is the main crite- rion, which determines the possibility of lasing by an organic compound on a certain frequency. The cross-section should exceed the threshold value estimated according to the following formula11 s¡¦1 34 �� 8pn2cn2f Dnftr , where n is the refractive index of the medium, c is the velocity of light, tr is the radiative lifetime of fluorescence, nf and Dnf are the frequency of maximum and the peak halfwidth of the fluorescence spectrum, respectively.80 Analysis of cross-sections of stimulated emission for the known laser dyes allows one to determine the threshold value s34 for the existence of lasing in organic com- pounds as s34>5610717 cm2 (Ref. 91). Spectral criteria for the occurrence of lasing in organic compounds were suggested 81 taking account of the relation between the cross-section of stimulated emission and spectral characteristics of a laser dye. Quantum-chemical criteria for the occurrence of laser radiation in organic compounds were also formulated.92, 93 Along with cross-section s34 the product of a photochemical reaction, thermodynamic and kinetic parameters of the reaction determine the efficiency of photochemical laser radiation.There are no rigorous quantitative criteria for the selection of lasing systems with proton phototransfer reactions. The following spectral-kinetic criteria for the selection of systems for the photo- chemical laser were suggested based on the analysis of the known laser systems with proton phototransfer reactions.9, 15 1. The initial compound (which absorbs light and in which the proton phototransfer reaction occurs) should absorb light strongly in excitation spectral range. The extinction coefficient should be greater than 104 litre mol71 cm71 at the excitation frequency. 2. The proton phototransfer reaction should be fast and efficient (i.e., with low efficiency of competing radiationless deactivation processes). The rate constants for the intermolecular and intramolecular proton phototransfer should be greater than 108 litre mol71 s71 and 109 s71, respectively. 3. The product of the proton phototransfer reaction should possess intense fluorescence.The fluorescence quantum yield should be greater than 0.2. 4. The acid-base properties of the dye should be changed significantly (DpKa>1) upon excitation to provide for the direct reaction of the proton transfer in the initial exd form of the dye and reverse reaction of the proton transfer in the product in the ground state. 5. The radiative transition in the product of the proton phototransfer reaction should possess a short radiative lifetime of fluorescence (tr<10 ns). 6. The rate of the reverse proton transfer reaction in the ground state should be significantly higher than the overall rate of the direct reaction of proton phototransfer in the excited state and the formation of the product of proton transfer in the ground state resulting from deactivation of the excited state. 7. The absorption spectra Sn S0, Sn S1 and Tn T1 of the initial form of the dye and reaction product of proton photo- transfer should possess minimum overlap with the fluorescence spectrum of the proton phototransfer product. The absorption coefficient at the frequency of lasing should not be higher than 0.01 cm71. 8. The steady-state concentration of molecules in the triplet state of the initial form of the dye and the proton phototransfer product should be low, which is ensured by a low rate constant for intersystem crossing from the S1 state and a large rate constant for intersystem crossing from the T1 state. 9. The initial form of the dye and the product of the proton phototransfer reaction should be photochemically stable. The majority of dyes listed in Tables 1 ¡À 3 fulfil the above- mentioned requirements. 2-Naphthol, potassium 7-hydroxynaph- thalene-1,3-disulfonate, 1,3-disulfo-7-naphthylammonium hyd- rogensulfate, and sodium salicylate are the exceptions. The extinction coefficients for these compounds at the excitation wavelength are smaller than 104 litre mol71 cm71.The radiative lifetime of fluorescence of the proton phototransfer products is greater than 10 ns.In spite of this, the reaction products of proton phototransfer of these compounds, except for the deprotonated form of 2-naphthol, lase. This is due to the fact that the numerical value of the criterion 5 permits selection of lasing dyes among all fluorophores. Aqueous 2-naphthol solution is also a useless laser system because the rate constant for the proton phototransfer for 2-naphthol in water is significantly smaller than 108 litre mol71 cm71.The overlap of the absorption and fluo- rescence spectra will be the smaller the higher Stokes' shift of fluorescence. In the formation of the lasing form as a result of reaction in the excited state, Stokes' shift is increased significantly (see Tables 1 ¡À 3). 128 BM Uzhinov, S I DruzhininIV.Acid-base laser systems Schaefer 94 was the first to report in 1968 on a photochemical laser based on a product of intermolecular acid photodissociation reaction of sodium 8-acetylaminopyrene-1,3,6-trisulfonate. In the ground state in basic solution the dye exists in the form of a trianion. In the excited state, the trianion dissociates to form a tetraanion.In the excitation by a lamp the laser radiation in a neutral solution is observed for the trication and in a basic solution for the tetraanion. The laser radiation spectrum in basic solution is shifted to longer wavelengths by 125 nm compared to the spectrum in neutral solution. The duration of the radiation pulse in basic solution (1400 ns) is greater than in neutral solution (250 ns).95 Laser radiation was obtained in 1970 from an ethanolic solution of sodium salicylate upon laser-induced excitation.96 The species that lased was not identified.However, the data then available and current data on fluorescence of sodium salicylate in ethanol allow assignment of this radiation to the product of intramolecular proton phototransfer to the oxygen of the carboxy group.97 For the first time lasing of a product of intramolecular proton phototransfer and identification of a radiating species was reported 98 in a study of stimulated emission of 2-(2-tosylamino- phenyl)-5-phenyl-1,3,4-oxadiazole and 2-(2-tosylaminophenyl)- benzoxazole in ethanol.The lasing species results from the intramolecular proton phototransfer from the nitrogen of the amino group of the phenyl ring to the nitrogen atoms of the oxadiazole and oxazole rings, respectively.The photochemical lasers known to date based on intermolecular and intramolecular reactions of proton phototransfer of organic compounds are listed in Tables 4 and 5. Table 4. Characteristics of photochemical lasers based on intermolecular proton phototransfer reactions of organic compounds. Reagents c1 c2 Solvent Radiation Laser Ref./mmol litre71 /mol litre71 range /nm efficiency (%) ArOH*+H2O ArO7*+H3O+ Potassium 7-hydroxynaphthalene- 1 56 Water 475 a ± 99 1,3-disulfonate+H2O 4.6 56 " 466 ± 484 b ± 15 4.6 56 Water, pH 5 460 ± 490 b ± 22 Sodium 8-hydroxypyrene- 0.2 56 Water 516 ± 532 c ± 100 1,3,6-trisulfonate+H2O 0.02 56 Water, pH 5.6 520 d ± 101 (2.9610716, Ref. 2) e 7-Hydroxycoumarin+H2O 5 44 EtOH, water (1:4) 460 b 10 102 1 56 Water 457 c ± 103 7-Hydroxy-4-methylcoumarin 5 44 EtOH, water (1:4) 460 b 7 102 +H2O 1 56 Water 430 ± 485 e ± 104 5 22 MeOH, water (3:2) 425 ± 545 a ± 105 7-Hydroxy-4-trifluoromethyl- 5 2.8 EtOH, water (19:1) 513 b 14.8 102 coumarin+H2O Ethyl 7-hydroxycoumarin- ± 56 Water 465 c ± 106 3-carboxylate+H2O 3-Cyano-7-hydroxy-4-methyl- 2 28 EtOH, water (1:1) 450 ± 510 a ± 107 coumarin+H2O ArOH* .. . NAlknH37n ArO7*+H47nNAlkn 7-Hydroxy-4-methylcoumarin ± ± Toluene 415 d ± 108 +Et3N 7-Hydroxy-4-methylcoumarin ± ± " 470 ± 480 d ± 108 +Et2NH ArNHAc*+B ArNAc7*+BH+ Sodium 8-acetylaminopyrene- ± ± Water 566 ± 574 a, b ± 95 1,3,6-trisulfonate+NaOH ArNHá3 +B ArNH2*+BH+ 1,3-Disulfo-7-naphthylammonium 19 56 Water, pH 1 450 ± 484 b ± 22 hydrogensulfate+H2O 10 56 Water, pH 0.5 Blue radiation c ± 22 10 56 Water 459 c ± 109 3,3-Dimethyl-2-(5-(7-R-3,3-dimethyl- ± ± EtOH 730 f 10 110 2,3-dihydropyrrolo[2,3-b]-pyridinio- 2-yliden)-penta-1,3-dienyl)-7R-2,3- dihydropyrrolo[2,3-b]pyridinium+OH± Excited state proton transfer dye lasers 129Table 4 (continued).Reagents c1 c2 Solvent Radiation Laser Ref. /mmol litre71 /mol litre71 range /nm efficiency (%) 3-Methoxybenzanthrone+HClO4 30 0.02 EtOH 540 ± 660 d ± 111 3-Methoxybenzanthrone+AcOH 2.5 17.5 AcOH 563 ± 586 ± 33 606 ± 627 d 0.9 7-Ethyl-4-methylcoumarin 1 ± EtOH 485 a ± 112 +HCl 4,6-Dimethyl-7-methylamino- 1.5 ± " 430 ± 525 a 5 113 coumarin+HCl ± 0.1 EtOH, water (24 : 1) 484 c ± 115 7-Ethylamino-4,6-dimethyl- ± 0.1 Ditto 487 c ± 114 coumarin+HCl 2,3,6,7-Tetrahydro-1H,5H-benzo- 2 0.2 " 474 ± 548 a 4.8 115 pyrano[6,7,8-ij]quinolizin-11-one +H2SO4 9-Methyl-2,3,6,7-tetrahydro- 2 0.15 " 525 ± 556 a 10 15 1H,5H-benzopyrano[6,7,8-ij]quino- lizin-11-one +H2SO4 N-Phenylacridone+CF3COOH 2.5 0.14 Toluene 472 d 0.2 33 3-Methoxybenzanthrone+CF3COOH 2.5 0.13 " 611 ± 641 d 2.5 33 5-Phenyl-2-(4-pyridyl)oxazole 0.86 1.80 EtOH 506 ± 520 a 0.4 116 +AcOH 0.86 2.35 " 512 ± 522 a 0.6 116 0.86 2.85 " 510 ± 520 a 1.0 116 0.86 3.75 " 505 ± 517 a 2.0 116 0.96 4.60 " 501 ± 515 a 2.6 116 5-(Methoxyphenyl)-2-(4-pyridyl)- 0.70 0.92 " 570 ± 594 a 2.7 116 oxazole+AcOH 0.70 1.62 " 554 ± 589 a 6.1 116 0.70 2.26 " 560 ± 585 a 7.8 116 0.70 2.68 " 550 ± 583 a 9.5 116 0.70 3.69 " 549 ± 583 a 12 116 0.70 4.57 " 545 ± 582 a 16 116 5-Phenyl-2-(2-quinolyl)-oxazole 0.71 5.85 " 514 ± 534 a 7.9 116 +AcOH 5-Phenyl-2-(4-quinolyl)-oxazole 0.86 5.57 " 512 ± 521 a 2.3 116 +AcOH 1,4-Bis(5-phenyloxazol-2-yl)benzene 0.4 ± MeCN 479 ± 490 a 3.6 42 +HClO4 1,4-Bis(5-phenyloxazol-2-yl)benzene 0.4 ± CF3COOH 460 ± 476 a 17.0 42 +CF3COOH 1,4-Bis(5-sulfophenyloxazol-2-yl)- ± ± EtOH, water (3 : 1) 489 ± 499 a 2.9 42 benzene+CF3COOH 1,4-Bis(5-sulfophenyloxazol-2-yl)- ± ± Ditto 485-499 a 5.5 42 benzene+HClO4 1,4-Bis(5-sulfophenyloxazol-2-yl)- ± ± Water 451 ± 458 a 7.1 42 benzene+H2SO4 1,4-Bis(5-phenyloxazol-2-yl)benzene 0.4 ± Dioxane 476 ± 491 a 14.2 42 +CF3COOH 1,4-Bis(5-p-tolyloxazol-2-yl)benzene ± ± " 487 ± 500 a 4.7 42 +CF3COOH C O*+HA C OH+*+A7 N* +HA +A7 N+* N* HA A7 N+* ...... 130 BM Uzhinov, S I DruzhininTable 4 (continued). Reagents c1 c2 Solvent Radiation Laser Ref. /mmol litre71 /mol litre71 range /nm efficiency (%) 7-Hydroxycoumarin 5 EtOH, water 487 b 0.9 102 2.7% HClO4 ± EtOH, water (24 : 1) 408, 487 b 4.0 117 7-Hydroxy-4-methylcoumarin 5 MeOH, 450 ± 600 a ± 105 0.37 N HClO4 (3 : 2) 5 EtOH, water 487 b 0.4 102 2.7% HClO4 ± EtOH, water (24 : 1) 400, 480 b 7.3 117 1.8 EtOH 477 ± 546 a ± 118 ± EtOH, water (3 : 2) 437 ± 544 a ± 119 7-Hydroxy-4-trifluorocoumarin 5 EtOH, water, 576 b 1.9 102 15% HClO4 ± EtOH, water (24 : 1) 530 b 10.7 117 ± EtOH, water (1 : 1) 513 b 11.8 117 0.75 Ditto 506 c ± 120 6-Glucosyl-7-hydroxy- ± Water 440 ± 490 c ± 121 coumarin 3-Cyano-7-hydroxycoumarin ± EtOH, water (7 : 3) 490 ± 520 c ± 122 3-Cyano-7-hydroxy-4-methyl- 2 EtOH, water (9 : 1), 440 ± 505 a ± 107 coumarin 2.5 mM HClO4 3-Cyano-7-hydroxy-4-trifluoro- ± EtOH, water (24 : 1) 543 b 12.6 117 methylcoumarin ± EtOH, water (1 : 1) 543 b 6.5 117 Two reactions simultaneously 7-Hydroxy-4-methylcoumarin ± ± EtOH, water 370 ± 530 d ± 123 +H2O 7-Hydroxy-4-trifluoromethyl- 5 ± EtOH, water (50%, 510 ± 595 b 10 102 coumarin+H2O 35%), 15% HClO4 5H-9-Diethylamino-5-imino- 0.14 3.3 EtOH, KOH 610 ± 715 f ± 38 benzo[a]phenoxazine+H2O (3 mmol litre71) Note.The following designations are adopted. c1 and c2 are concentrations of the first and second components, respectively. Excitation source : a nitrogen laser (337 nm); b excimer laser (308 nm); c pulse lamp; d the second harmonic of a ruby laser (347.1 nm). e Cross-section of stimulated emission estimated according to the equation s34=I1/2t0,101 where I1/2 is the intensity of light leading to half the fluorescence intensity, t 0 was taken from Ref. 26. f The second harmonic of a YAG: Nd3+-laser (532 nm). O R OH O O R O HO * * ArOH* +H2O ArO7*+H3O+ O R OH ; O O R O HO * * C NH*+H2O C NH2 +*+OH7 Table 5.Characteristics of photochemical lasers based on intramolecular proton phototransfer reactions of organic compounds. Reagent c Solvent Radiation range Laser Ref. /mmol litre71 /nm efficiency (%) 3-Hydroxyflavone 1.64 Methylcyclohexane 518 ± 545a 1.2b 53 1.64 Dioxane 535a ± 53 3.0 MeCN 526a ± 124 3.0 Acetone 526a ± 124 H O O H O O * * Excited state proton transfer dye lasers 131Table 5 (continued).Reagent c Solvent Radiation range Laser Ref. /mmol litre71 /nm efficiency (%) 3,30,40,7-Tetrahydroxyflavone 2.0 Dioxane 544 ± 570a 0.14b 124 Sodium salicylate 1 EtOH 395 ± 417a ± 96 1 Dioxane 390 ± 411c 7 125 Salicylamide 1 DMF 439c 5 126 2-(Benzimidazol-2-yl)phenol 2.1 Dioxane 460 ± 490c 14.5 56 2.0 MeOH 450 ± 480c 6.0 56 1.9 EtOH 454 ± 480c 3.0 56 2.6 MeCN 459 ± 489c 9.0 56 1.9 DMF 463 ± 495c 11.5 56 2-(Benzimidazol-2-yl)-4-methylphenol 1.2 Dioxane 475 ± 522a 15.5 56 2-(Benzimidazol-2-yl)-4-fluorophenol 0.7 MeCN 465 ± 510a 10 56 1 Polymethylmethacrylate 487 ± 499a 1 127 2-(Benzimidazol-2-yl)-4-methoxyphenol 1 Cyclohexane, 509 ± 537a 5.5 56 Dioxane 1.4 " 514 ± 552a 9.0 56 2,5-Bis(benzimidazol-2-yl)hydroquinone 1 Cyclohexane, 509 ± 542a 8.0 56 Dioxane 1 MeCN 507 ± 540a 10.0 56 1.4 Dioxane 515 ± 549a 13.5 56 1.5 DMF 515 ± 553a 7.0 56 Methyl 2-(2-hydroxyphenyl)benz- 0.5 Polymethylmethacrylate 489 ± 499a 0.5 128 imidazole-5(6)-carboxylate Methyl 2-(5-fluoro-2-hydroxyphenyl)- 0.5 " 499 ± 517a 1.8 128 benzimidazole-5(6)-carboxylate Copolymer of allyl-2-(2-hydroxyphenyl)- 0.5 " 490 ± 504a 1.4 128 benzimidazole-5(6)-carboxylate and methyl methacrylate Copolymer of allyl-2-(5-fluoro-2-hydroxy- 0.5 " 502 ± 521a 11.3 128 phenyl)benzimidazole-5(6)-carboxylate and methyl methacrylate 3,6-Bis(benzoxazol-2-yl)hydroquinone ± THF 650a, ± 129 620 ± 690d 4-Methoxy-3,6-bis(benzoxazol-2-yl)- ± " 615a, ± 129 phenol 590-690d 3,6-Bis(benzoxazol-2-yl)pyrocatechol ± " 560a, ± 129 540 ± 610d 2,20-Bipyridyl-3,30-diol 3 Dioxane 490 ± 573a 12 130 Benzene 495 ± 567a 3 63 ec=20 cm71 Dioxane 494 ± 567a 2 63 Cyclohexane 492 ± 572a 4 63 5-Methyl-2,20-bipyridyl- 3 Dioxane 503 ± 564a 6.5 130 3,30-diol 5,50-Dimethyl-2,20-bipyridyl- 3 " 503 ± 573a 7.2 130 3,30-diol O H O R O H O R * * * * O H N O H N 132 BM Uzhinov, S I DruzhininV.Losses in photochemical lasers The efficiency of dye lasing is determined by the relationship between the light amplification and losses. The losses are classified as constant and induced losses.The former are the losses in the resonator and at the mirrors. In dye lasers overabsorption of the laser radiation by the dye in the ground state (for a photochemical laser, by the components of acid-base interaction) belong to the constant losses in addition to those mentioned above.The constant losses are time independent. The induced losses in dye lasers are related to the absorption of lasing by short-living intermediate species produced by the excitation light. Induced losses in photochemical lasers unlike ordinary lasers may occur due to photoprotolytic reactions. Let us consider these induced losses. 1. Absorption of the laser radiation by the product of a photochemical reaction in the excited singlet [terms N3s35(n) and N30s3050 (n) in the equation (7)] and triplet [terms N6s67(n) and N60s6070 (n)] states of the components of the acid-base interaction. Acid-base systems with simultaneous lasing of the initial compound and the photoreaction product are the most valuable from the practical viewpoint.In the selective resonator of such a system, it is possible to attain laser radiation tuned over a wide spectral range, which exceeds the range of tuning for the individ- ual components of the acid-base system. Lasing of the initial compound and the reaction product separately does not necessa- rily imply their simultaneous lasing. Thus 2-heteryloxazoles and their cations fluoresce efficiently and lase separately.40 However, solutions with simultaneous efficient fluorescence of both the initial heteryloxazole and cation, do not lase at certain ratio of the components.As the concentration of a proton donor (acetic acid) in ethanolic solutions of 2-heteryloxazoles is increased, the quantum yields of fluorescence of the initial form are decreased, and a band of fluorescence of a protonated form resulting from the proton phototransfer appears in the longwave region of the spectrum,30 and the efficiency of laser radiation of the initial form drops to zero at low concentrations of acetic acid.At certain concentrations, both forms do not lase. At higher acetic acid concentrations, the laser radiation of the photoreaction product appears and the efficiency of this radiation increases with the increase in the acid concentration.116 Both the neutral and the protonated forms of 2-heteryloxazoles cause additional losses, which decrease stimulated emission by the corresponding con- jugated acid-base form. For this reason, it is impossible to produce two-band laser radiation in solutions of 2-heteryloxazoles.The losses due to the neutral form in the lasing by the cations result from the Sn/S1 absorption of the neutral forms. The losses due to the cations in the lasing by the neutral forms, in addition to Sn/S1 absorption in the region of stimulated emission of the neutral forms, may result from slow dissociation of the cations in the ground state.116 2.Light absorption by decay products of a lasing species. Reactions of electron photosplitting are typical of the aro- matic compounds with the electron-donor group (OR, NR2, O7). The thus formed solvated electron has a broad absorption spectrum,131 which can overlap with that of laser radiation of a photochemical laser. Thus flash lamp excitation of an aqueous solution of sodium 8-hydroxypyrene-1,3,6-trisulfonate (SHPTS) induced losses in the photochemical laser that are related to the absorption of the laser radiation from the deprotonated form of SHPTS by the hydrated electron produced from this excited form.132 The light absorption by the hydrated electron leads to a decrease in the efficiency and narrows the lasing spectrum of SHPTS.In the laser excitation, the induced loses in this laser are small.101 A decrease in the hydrated electron concentration due to its interaction with electron acceptors results in a decrease in these induced losses and an increase in the laser radiation efficiency of SHPTS in the lamp excitation.132 If the 7-aminonaphthalene-1,3-disulfonate dianion is formed in acidic solutions by the reaction of an acid photodissociated monoanion with the protonated amino group, the efficiency of the lasing upon pulse photoexcitation is considerably higher com- pared to that upon direct excitation from the ground state in neutral solutions.22 This increase in efficiency is rationalised as a decrease in losses, due to the induced Tn/T1 absorption of light by the 7-aminonaphthalene-1,3-disulfonate dianion upon proto- nation of the amino group of the dianion triplet (s67 < s6070 ) in acidic solutions and a decrease in losses, caused by the light absorption by the hydrated electron, as a result of the effective reaction of the electron with the proton.VI. Tunable photochemical lasers Systems with intermolecular relaxation processes that allow excitation of two or several different lasing species are promising for designing lasers tunable over a wide spectral range.This can be achieved in systems with electron energy transfer if both the donor and acceptor lase and in systems with fast reversible photo- chemical reactions provided both the initial species and the reaction product lase simultaneously.9 Favourable relative dispo- sition of the spectra of laser radiation of the components in binary systems with energy transfer and in systems with photoprotolytic reactions enables generation of laser radiation over a wide spectral range in a selective resonator.The acid-base systems with simultaneous laser radiation of both photoprotolytic forms are few. In the majority of photo- Table 5 (continued). Reagent c Solvent Radiation range Laser Ref./mmol litre71 /nm efficiency (%) N-[2-(5-Phenyl-1,3,4-oxadiazol- ± EtOH 530 a ± 98 2-yl)phenyl]toluene-p-sulfamide N-[2-(benzoxazol-2-yl)phenyl]toluene- ± " 530 a ± 98 p-sulfamide Note. a Excitation by a nitrogen laser (337 nm). b The ratio of peak power to peak power of laser radiation of Rhodamine 6G. c Excitation by an excimer laser (308 nm). d Spectral range of amplification.* * N H N Tos N H N Tos Excited state proton transfer dye lasers 133chemical lasers (see Tables 4 and 5), stimulated light emission by the reaction product only is observed. This narrows substantially the possibility for creation of an increased range of tunable radiation in dye lasers. Binary mixtures were suggested to over- come this difficulty. In these mixtures, one or both components participate in photoprotolytic reactions.133, 134 Realisation of a large Stokes' shift of fluorescence, due to adiabatic reactions of proton phototransfer allows the selection of binary solutions where the fluorescence band of one of the components lies in the spectral range between the absorption band and the fluorescence band of the second component.This allows one to create active media of lasers with an expanded range of the laser radiation tuning within the limits of the total luminescence band of the binary mixture components. To increase substantially the tuning range of laser radiation in binary mixtures with photoprotolytic reactions it is necessary that first, the fluorescence bands are shifted relative to each other to make the total amplification band noticeably wider than the amplification bands of the individual components.Second, the energy transfer between components should not occur, that is, the absorption band of one component should not overlap with the fluorescence band of the other component. These requirements can be met if systems with a high Stokes' shift of fluorescence are used, e.g.systems with photoprotolytic reactions.134 In coherent excitation, compounds should possess substantial absorption at the excitation wavelength. In lamp excitation the absorption spectra of the components should have minimum overlap to utilise efficiently the pump energy. For some binary mixtures of this type, broadening of the tuning range or shift of the maximum of laser radiation is observed at a certain ratio of the components (Table 6).The spectrum of stimulated emission of 2,20-bipyridyl-3,30- diol in which intramolecular proton phototransfer occurs exhibits a blue shift in dioxane upon addition of 7-ethylamino-6-methyl-4- trifluoromethylcoumarin.63 This effect depends on the relative concentration of the components. If spectra of laser radiation of components of a binary mixture are far removed from each other, the mutual influence of the components on the spectral position of their laser radiation is absent. The spectrum of stimulated emission of a mixture of 1,4-bis(2-methylstyryl)benzene (0.861073 mol litre71) and 3-hydroxyflavone (361073 mol litre71) which undergoes intramolecular proton phototrans- fer, exhibits two peaks at 420 and 535 nm in dioxane.133 These maxima coincide with those of stimulated emission of the individ- ual components in the same solvent and their relative intensities depend on the relative concentrations of the components.A similar picture is observed for a solution of 4,40-diphenylstilbene (1.261073 mol litre71) and 3-hydroxyflavone (1.6461073 mol litre71) in dioxane.Two maxima at 408 and 535 nm,133 which correspond to the stimulated emission of individual components, are observed in the spectrum of stimu- lated emission of a mixture. References 1. F P Shaefer (Ed.) Dye Lasers (Berlin: Springer, 1973) 2. Yu G Basov Zh. Prikl. Spektrosk. 49 887 (1988) 3. A Penzkofer Appl. Phys. B., Laser Opt. 46 43 (1988) 4. A M Trozzolo, A Dienes, C V Shenk J.Am. Chem. Soc. 96 4699 (1974) 5. B I Stepanov (Ed.) Katalog Aktivnykh Lazernykh Sred na Osnove Rastvorov Organicheskikh Krasitelei i Rodstvennykh Soedinenii (The Catalogue of Active Laser Media Based on Solutions of Organic Dyes and Related Compounds) (Minsk: Institute of Physics of Academy of Sciences of Bel. SSR, 1977) Table 6. Characteristics of photochemical lasers based on binary dye systems.Binary dye system c1 c2 l17l2 or /mmol litre71 /mmol litre71 l /nm 7-Hydroxy-4-methyl- 2.4 0 426 ± 515 coumarin a+sodium 2.4 0.15 440 ± 523 8-hydroxypyrene-1,3,6- 0 0.5 507 ± 534 trisulfonate a in EtOH ± water solution (3:7) 6-Glucosyl-7-hydroxy- 2.4 0 436 ± 516 coumarin a+sodium 2.4 0.15 441 ± 527 8-hydroxypyrene-1,3,6- 0 1.0 506 ± 533 trisulfonate a in water 7-Diethylamino-4-methyl- 1.6 0 450 ± 510 coumarin a+sodium 1.6 0.12 453 ± 525 8-hydroxypyrene-1,3,6-tri- 0 0.7 510 ± 535 sulfonate a in EtOH ± water solution 1,4-Bis(5-phenyl-1-propio- 0.5 0 404 ± 418 nyl-D2-pyrazolin-3-yl)ben- 0.5 4 416 ± 470 zene+7-hydroxy-4-methyl- 0 2 429 ± 497 coumarin a in EtOH ± water solution, (9:1), 0.05 mol litre71 AcONa 1,4-Bis(5-phenyl-1-propionyl- 0.5 0 405 ± 417 D2-pyrazolin-3-yl)benzene+ 0.5 1 413 ± 457 7-diethylamino-4-methyl- 0 2 435 ± 473 coumarin b in dioxane ± water solution, (19:1) 3-Hydroxyflavone a+ 0 1.64 528 ± 540 1,1,4,4-tetraphenylbuta- 3.5 1.64 509 ± 540 diene in methylcyclo- 4.5 1.64 500 ± 534 hexane 4.5 1.24 496 ± 528 4.5 0 490 ± 525 2-(Benzimidazol-2-yl)-4- 1.3 0 495 methylphenol a+2,5-bis- 1.2 0.1 502 (benzimidazol-2-yl)hydro- 1.1 0.2 505 quinone a in dioxane 0.9 0.4 509 0.8 0.5 511 0.7 0.6 515 0.6 0.7 516 0.4 0.9 519 0.2 1.1 525 0 1.3 527 2-(Benzimidazol-2-yl)-4- 2.6 0 474 methylphenol a+2,5-bis- 2.2 0.1 478 (benzimidazol-2-yl)hydro- 2.0 0.3 488 quinone a in acetonitrile 1.6 0.5 496 1.3 0.5 503 0.9 0.7 512 0.4 0.9 520 0 1.0 524 Note.The following designations are adopted: c1 is the concentration of the first component of the binary dye system, c2 is the concentration of the second component of the binary dye system, l17l2 is the range of tuning of lasing, l is the wavelength of spectral maximum of laser radiation.The data for the first five binary dye systems are taken from Ref. 134, for the next system from Ref. 133, and for the two last systems from Ref. 56. a The component that undergoes proton phototransfer reaction. b The component that forms a hydrogen-bond complex in the excited state. 134 BM Uzhinov, S I Druzhinin6. V V Gruzinskii Tablitsy Aktivnykh Sred OKG na Mnogoatomnykh Organicheskikh Molekulakh (The Tables of Active Media of Optical Quantum Generators Based on Polyatomic Organic Molecules) (Minsk: Institute of Physics of Academy of Sciences of Bel.SSR, 1977) 7. M Maeda Laser Dyes (Properties of Organic Compounds for Dye Lasers) (New York: Academic Press, 1984) 8. L K Denisov, N A Kozlov, B M Uzhinov Organicheskie Soedine- niyaìAktivnye Sredy Lazerov (Organic Compounds as Active Media of Lasers) (Moscow: Central Research Institute `Elektronika', 1980) 9. B M Uzhinov, V I Yuzhakov, T A Dolenko Kvantovaya Elektron. 19 7 (1992) a 10. A A Ishchenko Kvantovaya Elektron. 21 513 (1994) a 11. B I Stepanov, A N Rubinov Usp. Fiz. Nauk 95 45 (1968) b 12. P Suppan Chemistry and Light (Cambridge: Royal Society of Chemistry, 1994) 13. MA Fox,MChanon (Eds) Photoinduced Electron Transfer (Amster- dam: Elsevier, 1988) 14. S A Krashakov, B M Uzhinov Kvantovaya Elektron. 9 2336 (1982) a 15.B M Uzhinov, Doctoral Thesis in Chemical Sciences, Moscow State University, Moscow, 1987 16. I Yu Martynov, A B Demyashkevich, B M Uzhinov, M G Kuz'min Usp. Khim. 46 3 (1977) [Russ. Chem. Rev. 46 1 (1977)] 17. C M Harris, B K Selinger J. Phys. Chem. 84 891 (1980) 18. S C Lahiri J. Sci. Ind. Res. 38 492 (1979) 19. A Weller Z. Phys. Chem. Neue Folge 18 163 (1958) 20.N M Trieff, B R Sundheim J. Phys. Chem. 69 2044 (1965) 21. H Shizuka, K Tsutsumi Z. Phys. Chem. Neue Folge 122 129 (1980) 22. S I Druzhinin, Candidate Thesis in Chemical Sciences, Moscow State University, Moscow, 1983 23. S G Schulman, L S Rosenberg,W R Vincent J. Am. Chem. Soc. 101 139 (1979) 24. N K Zaitsev,A B Demyashkevich,M G Kuz'min Khim. Vys. Energ. 13 331 (1979) c 25. Th FoÈ rster, S Volker Z.Phys. Chem. Neue Folge 97 79 (1975) 26. N Agmon, D Huppert, A Masad, E Pines J. Phys. Chem. 95 10407 (1991) 27. L M Rubeko, I V Krasnov, N A Kozlov, L K Denisov, B M Uzhinov Dokl. Akad. Nauk SSSR 240 1157 (1978) d 28. O A Ponomarev, E R Vasina, S N Yarmolenko, V G Mitina Zh. Obshch. Khim. 55 179 (1985) e 29. B D Bursulaya, S I Druzhinin, B M Uzhinov J. Photochem.Photobiol. A: Chem. 92 163 (1995) 30. S I Druzhinin, S A Krashakov, I V Troyanovsky, B M Uzhinov Chem. Phys. 116 231 (1987) 31. S I Druzhinin, G M Rodchenkov, B M Uzhinov Chem. Phys. 128 383 (1988) 32. S A Krashakov, Candidate Thesis in Chemical Sciences, Moscow State University, Moscow, 1987 33. S A Krashakov, A I Akimov, G M Rodchenkov, B M Uzhinov Zh. Prikl. Spektrosk. 42 896 (1985) 34.U Brackmann Lambdachrome Lasergrade Dyes (Goettingen: Lambda Physics GmbH, 1986) 35. B D Bursulaya, S I Druzhinin, M A Kirpichenok, I I Grandberg, B M Uzhinov Zh. Obshch. Khim. 63 1397 (1993) e 36. Th FoÈ rster Z. Elektrochem. 54 42 (1950) 37. S I Druzhinin, B D Bursulaya, B M Uzhinov Zh. Prikl. Spektrosk. 59 248 (1993) 38. E M Goryaeva, A V Shablya Zh. Prikl. Spektrosk. 43 750 (1985) 39. A V Butenin, B Ya Kogan, in Lazery na Osnove Slozhnykh Organ- icheskikh Soedinenii i ikh Primenenie (Tez. Dokl. III Vsesoyuz. Konf.) [Lasers Based on Complex Organic Compounds and Their Applica- tions (Abstracts of Reports at the Third All-Union Conference)] (Minsk: Institute of Physics of Academy of Sciences of Bel. SSR, 1980) p. 254 40. S I Druzhinin, S A Krashakov, I N Tur, L Sh Afanasiadi, I V Troyanovskii, B M Uzhinov Kvantovaya Elektron. 14 2024 (1987) a 41. I B Berlman Fluorescence Spectra of Aromatic Molecules (London: Academic Press, 1971) 42. S I Druzhinin, G M Rodchenkov, B M Uzhinov Zh. Prikl. Spektrosk. 48 711 (1988) 43. M G Kuz'min, Yu Yu Kulis Dokl. Akad. Nauk SSSR 200 630 (1971) d 44. S I Druzhinin, B M Uzhinov Chem. Phys. 78 29 (1983) 45.W Klopffer Adv. Photochem. 10 311 (1977) 46. Chem. Phys. 136 (1989) 47. J. Phys. Chem. 95 (25) (1991) 48. S J Formosinho, L G Arnaut J. Photochem. Photobiol., A: Chem. 75 21 (1993) 49. J Catalan, F Toribio, A U Acuna J. Phys. Chem. 86 303 (1982) 50. B J Schwartz, L A Peteanu, C B Harris J. Phys. Chem. 96 3591 (1992) 51. O S Wolfbeis,M Leiner, P Hochmuth Ber. Bunsenges.Phys. Chem. 88 759 (1984) 52. T P Dzugan, J Schmidt, T J Aartsma Chem. Phys. Lett. 127 336 (1986) 53. P Chou, D McMorrow, T J Aartsma, M Kasha J. Phys. Chem. 88 4596 (1984) 54. H Bulska J. Lumin. 39 293 (1988) 55. H Bulska, A Grabowska, Z R Grabowski J. Lumin. 35 189 (1986) 56. A Costela, F Amat, J Catalan, A Douhal, J M Figuera, J M Munoz, A U Acuna Opt. Commun. 64 457 (1987) 57.A Douhal, F Amat-Guerri, M P Lillo, A U Acuna J. Photochem. Photobiol. A: Chem. 78 127 (1994) 58. A Costella, J M Munoz, A Douhal, J M Figuera, A U Acuna Appl. Phys. B, Lasers Opt. 49 545 (1989) 59. A Mordzinski, W Kuehnle J. Phys. Chem. 90 1455 (1986) 60. N I Nizhegorodov, V V Nikiforov, V P Zvolinskii, L Sh Afanasiadi, I N Tur, B M Krasovitskii Dokl. Akad. Nauk SSSR 308 1410 (1989) d 61.A L Huston, G W Scott J. Phys. Chem. 91 1408 (1987) 62. K H Grellmann, A Mordzinski, A Heinrich Chem. Phys. 136 201 (1989) 63. J Sepiol, H Bulska, A Grabowska Chem. Phys. Lett. 140 607 (1987) 64. D A Parthenopoulos, D McMorrow, M Kasha J. Phys. Chem. 95 2668 (1991) 65. A P Ivanov Opt. Spektrosk. 8 352 (1960) f 66. V L Broude, V S Mashkevich, A F Prikhod'ko, N F Prokopyuk, M S Soskin Fiz.Tverd. Tela 4 2976 (1962) 67. A N Rubinov, A P Ivanov Opt. Spektrosk. 17 753 (1964) f 68. A M Ratner Zh. Teor. Fiz. 34 115 (1964) 69. B I Stepanov, A N Rubinov Zh. Prikl. Spektrosk. 4 222 (1966) 70. A N Rubinov, B I Stepanov Opt. Spektrosk. 22 605 (1967) f 71. D L Stockman,W R Malory, F K Tittel Proc. IEEE 52 341 (1964) 72. B I Stepanov,A N Rubinov,V A Mostovnikov Zh.Eksp. Teor. Fiz., Pis'ma Red. 5 144 (1967) 73. P Sorokin, J Lankard IBM J. Res. Dev. 10 162 (1966) 74. V V Gruzinskii, V I Danilova, K M Degtyarenko, T N Kopylova, B M Krasovitskii, N A Popova, E G Yushko Zh. Prikl. Spektrosk. 47 846 (1987) 75. M M Loiko, A N Rubinov Pribory Tekh. Eksper. 201 (1972) 76. B I Stepanov, N N Bychkov, L V Levshin, B A Konstantinov, A I Akimov, V E Mnuskin, A N Tokareva, B F Trinchuk, A I Sopin, B M Uzhinov, S I Druzhinin Pis'ma Zh.Eksp. Teor. Fiz. 14 653 (1988) 77. M V Bondar, O V Przhonskaya, E A Tikhonov, N M Fedotkina Zh. Prikl. Spektrosk. 52 534 (1990) 78. N A Borisevich, I I Kalosha, V A Tolkachev Zh. Prikl. Spektrosk. 19 1108 (1973) 79. B I Stepanov Metody Rascheta Opticheskikh Kvantovykh Genera- torov na Krasitelyakh pri Monokhromaticheskom Vozbuzhdenii, (Pre- print) Ch. 1 [Methods of Calculation of Optical Quantum Generators Based on Dyes with Monochromatic Excitation, Part 1 (Preprint)] (Minsk: Institute of Physics of Academy of Sciences of Bel. SSR, 1968) 80. A P Simonov, Doctoral Thesis in Physicomathematical Sciences, Research Institute of Physical Chemistry, Moscow, 1975 81. L K Denisov, B M Uzhinov Khim.Geterotsikl. Soedin. 6 723 (1980) g 82. L D Derkacheva Opt. Spektrosk. 15 138 (1963) f 83. M G Kuz'min Dokl. Akad. Nauk SSSR 151 1371 (1963) d 84. E M Goryaeva, A A Krasheninnikov, A V Shablya Opt. Spektrosk. 47 284 (1979) f 85. A U Khan, M Kasha Proc. Natl. Acad. Sci. USA 80 1767 (1983) 86. M Kasha Acta Phys. Pol. A 71 717 (1987) 87. M Kasha J. Chem. Soc., Faraday Trans. 2 82 2379 (1986) 88. N P Ernsting, B Nikolaus Appl. Phys. B, Lasers Opt. 39 155 (1986) 89. W Al-Soufi,K H Grellman, B Nickel J. Phys. Chem. 95 10503 (1991) Excited state proton transfer dye lasers 13590. H Eizenberg, B Nickel, A Ruth,W Al-Soufi, K H Grellman, M Novo J. Phys. Chem. 95 10509 (1991) 91. G A Abakumov,M M Mestechkin, V N Poltavets, A P Simonov Kvantovaya Elektron. 5 1975 (1978) a 92. G V Maier, Doctoral Thesis in Physicomathematical Sciences, Tomsk State University, Tomsk, 1987 93. V P Zvolinskii, Candidate Thesis in Chemical Sciences, Russian Friendship Among People University, Moscow, 1994 94. F P Schaefer, in International Quantum Electronics Conference (Abstracts of Reports) Miami, USA 1968 95. F P Schaefer Angew. Chem. 82 25 (1970) 96. J A Myer, I Itzkan, E Kierstead Nature (London) 255 544 (1970) 97.P J Kovi, C L Miller, S Schulman Anal. Chim. Acta 61 7 (1972) 98. V V Nikiforov, Candidate Thesis in Physicomathematical Sciences, Russian University of People Friendship, Moscow, 1984 99. D Basting, F P Schaefer, B Steyer Appl. Phys. B, Lasers Opt. 3 81 (1974) 100. L M Rubeko, Candidate Thesis in Chemical Sciences, Moscow State University, Moscow, 1982 101. V E Joos,M Hauser Arab.J. Sci. Eng. (UK) 17 209 (1992) 102. L I Loboda, I V Sokolova, A Ya Il'chenko, T N Kopylova Kvantovaya Elektron. 13 183 (1986) a 103. B B Snavely, O G Peterson IEEE J. Quantum Electron. QE-4 540 (1968) 104. B C Fawcett IEEE J. Quantum Electron. QE-6 473 (1970) 105. A Dienes, C V Shank, R L Kohn IEEE. J. Quantum Electron. QE-9 833 (1973) 106. K H Drexhage, G R Erikson, G H Hawks, G A Reynolds Opt. Commun. 15 399 (1975) 107. M Takakusa, U Itoh Opt. Commun. 26 401 (1978) 108. L M Rubeko, A I Akimov, L K Denisov, B M Uzhinov Zh. Prikl. Spektrosk. 35 436 (1981) 109. M Maeda, Y Miyazoe Jpn. J. Appl. Phys. 11 692 (1972) 110. F A Mikhailenko, O V Moreiko, O V Przhonskaya, E A Tikhonov Kvantovaya Elektron. 7 572 (1980) a 111. L D Derkacheva, A I Krymova, V A Petukhov Kvantovaya Elektron. 10 636 (1983) a 112. R Srinivasan, R J Gutfeld, C S Angadiyavar, R W Dreyfus Chem. Phys. Lett. 25 537 (1974) 113. R J Gutfeld, B Welber, E E Tynan IEEE J. Quantum Electron. QE-6 532 (1970) 114. R Srinivasan IEEE J. Quantum Electron. QE-5 552 (1969) 115. N V Korol'kova,M G Reva, B M Uzhinov Kvantovaya Elektron. 14 837 (1987) a 116. S I Druzhinin, S A Krashakov, I V Troyanovskii, A I Akimov, I N Tur, L Sh Afanasiadi, B M Uzhinov Zh. Prikl. Spektrosk. 48 391 (1988) 117. L I Loboda, I V Sokolova, L M Degtyarenko, A Ya Il'chenko, A V Kropachev Izv. Vyssh. Uchebn. Zabed., Fiz. 31 103 (1988) 118. E D Stokes, F B Dunning, R F Stebbings, G K Walters, R D Rundel Opt. Commun. 5 267 (1972) 119. C V Shank, A Dienes, A M Trozzolo, J A Myer Appl. Phys. Lett. 16 405 (1970) 120. E J Schimitschek, J A Trias, P R Hammond, R L Atkins Opt. Commun. 11 352 (1974) 121. G Marowsky IEEE J. Quantum Electron. QE-9 245 (1973) 122. M Takakusa, U Itoh, H Anzai, H Masuko, T Sato Jpn. J. Appl. Phys. 17 1461 (1978) 123. S Yamashita Rep. Fac. Sci. Shizuoka Univ. 23 15 (1989) 124. D A Parthenopoulos, M Kasha Chem. Phys. Lett. 146 77 (1988) 125. A U Acuna, F Amat-Guerri, J Catalan, A Costela, J M Figuera, J M Munoz Chem. Phys. Lett. 132 567 (1986) 126. A U Acuna, A Costela, J M Munoz J. Phys. Chem. 90 2807 (1986) 127. A U Acuna, F Amat-Guerri, A Costela, A Douhal, J M Figuera, F Florido, R Sastre Chem. Phys. Lett. 187 98 (1991) 128. M L Ferrer, A U Acuna, F Amat-Guerri, A Costela, J M Figuera, F Florido, R Sastre Appl. Opt. 33 2266 (1994) 129. A Grabowska, J Sepiol, C Rulliere J. Phys. Chem. 95 10493 (1991) 130. L Kaczmarek, B Nowak, J Zukowski, P Borowicz, J Sepiol, A Grabowska J. Mol. Structure 248 189 (1991) 131. E Hart,M Anbar The Hydrated Electron (New York: Wiley, 1970) 132. L M Rubeko, I V Krasnov, G A Malyshev, S A Krashakov, N A Kozlov, L K Denisov, B M Uzhinov Zh. Prikl. Spektrosk. 32 262 (1980) 133. P Chou, T J Aartsma J. Phys. Chem. 90 721 (1986) 134. A I Akimov, N V Korol'kova, N V Kurokhtin, M B Levin, M G Reva, B M Uzhinov, V V Fadeev Kvantovaya Elektron. 15 1001 (1988) a a�Quantum. Electron. (Engl. Transl.) b�Physics-Uspekhi (Engl. Transl.) c�High Energy Chem. (Engl. Transl.) d�Dokl. Chem. Technol., Dokl. Chem. (Engl. Transl.) e�Russ. J. Gen. Chem. (Engl. Transl.) f�Opt. Spectrosc. (Engl. Transl.) g�Chem. Heterocycl. Compd. (Engl. Transl.) 136 BM Uzhinov,
ISSN:0036-021X
出版商:RSC
年代:1998
数据来源: RSC
|
| 4. |
Types of cationic complexes based on oxocentered tetrahedra [OM4] in crystal structures of inorganic compounds |
| |
Russian Chemical Reviews,
Volume 67,
Issue 2,
1998,
Page 137-155
Sergei V. Krivovichev,
Preview
|
|
摘要:
Abstract. The crystal structures of inorganic compounds compris- ing cationic complexes containing oxygen atoms coordinated tetrahedrally to metal atoms, or oxocentred groups [OM4], are considered. The linking of the [OM4] tetrahedra in the structures has been analysed and cationic complexes of different structures have been identified. The rules governing the linking of the [OM4] tetrahedra have been formulated and the cationic complexes have been subjected to a detailed systematic treatment on their basis.Data on the statistics of the bond lengths and bond angles in the [OM4] tetrahedra are presented. The bibliography includes 317 references. I. Introduction One of the approaches to the description of crystal structures is the identification in the latter of cations as the central atoms and of anions as ligands.However, a number of crystal structures can also be considered from the standpoint of the coordination of anions 1±7 and in particular of oxygen atoms (Al2O, Al3O,8, 9 Mg2O, Mg3O,10 ± 13 Li3O, Li4O, Li5O,14, 15 Na3O, Na4O, K3O, K4O,16, 17 etc. clusters). Some workers 18 ± 21 have used this approach for the description of crystal structures, identifying in the latter individual atomic groups formed by anions as the central atoms and by cations as the ligands.The development of this approach constitutes the subject of the crystal chemistry of compounds with oxocentred complexes, within the framework of which one considers `additional' oxygen atoms�atoms which do not enter into the composition of the traditional anionic com- plexes [TmOm] (T=Si, Ge, B, S, P, V, As, Se, etc.) and water molecules � as the coordination centres.We emphasise that the proposed method applies only to cationic complexes and does not alter the classification of structures based on the type of anionic groups. In most cases, the `additional' oxygen atoms are involved in the tetrahedral coordination of metal atoms and oxygen is thus the central atom in cationic [OM4] n+ complexes.We may note that the coordination of the `additional' oxygen atom in the complex originally studied structurally was not as a rule ana- lysed, but sometimes an oxocentred complex based on [OM4] groups was identified in connection with the main alternative description of the structure. For example, Sahl 22 described the structure of lanarkite Pb2O(SO4) on the basis of chains of [OPb2], consisting of edge-linked [OPb4] tetrahedra and sulfate groups [SO4].Apparently the first systematic study on this topic is that of Bergerhoff and Paeslack,19 where the authors specified only `additional' oxygen atoms as the centres for a series of tetrahedral complexes based on [OM4] groups. The calculation of the stoi- chiometric cation/additional oxygen atom ratios, which are some- times appreciably greater than unity, serves as the crystal- chemical basis for this approach.Thus in the structure of dolerophanite Cu2O(SO4),23, 24 the ratio is 2, which provides grounds for considering the `additional' oxygen atom as the coordination centre. Six oxocentred complexes based on [OM4] tetrahedra have been identified:19 a single tetrahedron, a chain, three types of layers, and one framework.Such a small structural diversity of [OM4] complexes is due to the fact that at the time when the above communication was written 19 (1968) few struc- tures with `additional' oxygen atoms were known. Later Carre et al.20 analysed a series of compounds with complexes based on oxocentred [OLa4] tetrahedra.They specified 20 five different types of complexes considered as derivatives of the oxocentred [OLa] layer. Bengtsson and Holmberg 21 published a review on the structural chemistry of crystalline and amorphous media contain- ing [OPb4] tetrahedra. Oxocentred [OPb4] tetrahedra have been found in glasses of the PbO ± PbF2 system.25 ± 27 They produce a three-dimensional framework made up of O± Pb ±O linkages and performing in essence a function analogous to that of the [SiO4] tetrahedra in silicate glasses.The [OCu4] tetrahedra are well known in organometallic chemistry as the central groups in copper(II) m4-oxo-complexes.28 ± 37 Ten types of [OCu4] com- plexes have been identified 38 ± 41 and their characteristic features have been noted: the cationic nature of [OMx] tetrahedral com- plexes; owing to the large size of the central atom and its relatively low charge (27), the tetrahedra are linked to one another not only via common corners but also via their edges and there is also a possibility of corners common to more than two tetrahedra (this accounts for the exceptional diversity of the types of complexes).S V Krivovichev, S K Filatov, T F Semenova St.-Petersburg State Univer- sity, Universitetskaya naberezhnaya 7/9, 199034 St.-Petersburg, Russian Federation. Fax (7-812) 218 13 44. Tel. (7-812)218 96 47. E-mail: flt@cryst.geol.pu.ru (S V Krivovichev) Received 11 September 1997 Uspekhi Khimii 67 (2) 155 ± 174 (1998); translated by A K Grzybowski UDC 548.736 Types of cationic complexes based on oxocentred tetrahedra [OM4] in the crystal structures of inorganic compounds S V Krivovichev, S K Filatov, T F Semenova Contents I.Introduction 137 II. The bond lengths in [OM4] complexes and the physical properties of compounds with [OM4] tetrahedra 138 III. Systematic treatment of cationic complexes based on [OM4] tetrahedra and the principles governing their descriptions 139 IV.Types of cationic [OM4] complexes 140 V. Statistics of the corner and edge-linking [OM4] tetrahedra 150 VI. Rules governing the linking of oxocentred [OM4] tetrahedra 151 VII. Statistics of theM±O bond lengths and M±O±Mbond angles in [OM4] complexes 151 VIII. Conclusion 152 Russian Chemical Reviews 67 (2) 137 ± 155 (1998) #1998 Russian Academy of Sciences and Turpion LtdInorganic compounds incorporating an oxygen atom with tetrahedral coordination involving metal atoms are examined in the present review and a systematic crystal-chemical description of the ways in which the oxocentred [OM4] groups are linked together to form cationic [OmMn] complexes is given.II. The bond lengths in [OM4] complexes and the physical properties of compounds with [OM4] tetrahedra The identification of the oxocentred cationic [OM4] complexes as structural units of a special type arose because of the high strength of the O±M bonds in these groups.Table 1 presents the average M±O distances (M=Cu, Sn, Pb, La) in structures with tetrahe- drally coordinated `additional' oxygen atoms OA and the anionic [TO]n complexes formed by the central atom T and the oxygen atoms OT as the ligands {[TO3], T=Se, As; [TO4], T=S, Cr, V, P, Ge; [TO6], T=Mo, Re}.Thus the averageM±OA andM±OT distances are 1.93 and 1.99 A respectively for M=Cu, 2.23 and 2.42 A for M=Sn, 2.33 and 2.69 A for M=Pb, and 2.42 and 2.60 A for M=La. We may note that bonds longer than 2.1 A were not taken into account in calculating the Cu ±O bond lengths.The OA ±M bond is on average shorter than OT ± M, which suggests a high bond strength in the oxocentred tetrahedral complexes and influences the physical properties of the chemical compounds. We shall consider as an example the crystal structure of georgbokiite Cu5O2(SeO3)2Cl2 (Fig. 1). In this structure, there are isolated groups (SeO3) with Se atoms involved in ternary `pyramidal' coordination.According to traditional crystal-chem- ical ideas, this structure is considered from the standpoint of the coordination of copper and selenium atoms. Three crystallo- graphically nonequivalent copper atoms form coordination poly- hedra with different structures and compositions: Cu(1)O3Cl2 � trigonal bipyramid; Cu(2)O4Cl2 and Cu(3)O5Cl � octahedra.Only the equatorial CuO4 fragments are indicated in Fig. 1a for the octahedra as the most stable groups. The Cu(3)O4 squares are linked via their edges, forming infinite CuO2 chains, extended z y Cu(2) Cu(1) Cu(3) z y Se Cu O Cl a b Figure 1. The crystal structure of georgbokiite Cu5O2(SeO3)2Cl2 in projection onto the yz plane.42 (a) Representation in the coordination polyhedra of copper; (b) `ball-and-stick' representation. Table 1.The M±O bond lengths for the `additional' oxygen atom OA in the [OM4] tetrahedra and the OT oxygen atom in the [TO3] triangular groups, [TO4] tetrahedra, or [TO6] octahedra. Compound M7OA /A M7OT /A Ref. Compound M7OA /A M7OT /A Ref. M=Cu M=Pb Cu5O2(SeO3)2Cl2 1.95 2.00 42 Pb2O(SO4) 2.30 2.66 22 (1.93 ± 1.98) (1.94 ± 2.05) (2.27 ± 2.33 (2.46 ± 2.85) KCu3OCl(SO4)2 1.92 2.01 43, 44 Pb3O2(SO4) 2.32 2.80 57, 58 (1.86 ± 1.98) (1.93 ± 2.08) (P21/m) (2.18 ± 2.43) (2.69 ± 2.95) Cu2O(SO4) 1.92 1.99 23, 24 Pb3O2(SO4) 2.36 2.62 59 (1.88 ± 2.00) (1.91 ± 2.07) (Cmcm) (2.32 ± 2.39) (2.55 ± 2.70) NaKCu3O(SO4)3 1.93 1.97 45 Pb3O2(SO4) 2.32 2.76 60 (1.91 ± 1.94) (1.92 ± 2.03) (P1) (2.12 ± 2.49) (2.55 ± 2.97) K2Cu3O(SO4)3 1.93 1.97 46, 47 Pb5O3(GeO4) 2.32 2.54 61 (1.92 ± 1.96) (1.93 ± 2.03) (2.19 ± 2.68) (2.14 ± 2.92) Na2Cu4O(PO4)2Cl 1.88 2.00 48 Pb19(VO4)2O9Cl4 2.32 2.77 62, 63 (1.85 ± 1.91) (1.92 ± 2.03) (2.18 ± 2.59) (2.36 ± 3.10) Cu4O(PO4)2 1.91 1.98 49, 50 Pb2O(CrO4) 2.30 2.78 64 ± 66 (1.90 ± 1.92) (1.92 ± 2.09) (2.28 ± 2.31) (2.46 ± 2.93) Cu2O(SeO3) 1.96 1.97 51 Pb8Cu(AsO3)2O3Cl3 2.40 2.57 67 (P21/n) (1.93 ± 1.97) (1.93 ± 2.02) (2.18 ± 2.57) (2.34 ± 2.89) Cu2O(SeO3) 1.94 2.02 (P213) (1.92 ± .97) (1.98 ± 2.08) M=La Cu5O2(PO4)2 1.93 1.96 52 La3O2(ReO6) 2.38 2.60 68 (1.91 ± 1.94) (1.90 ± 2.06) (P21/m) (2.32 ± 2.45) (2.42 ± 2.86) Cu4O(AsO4)2 1.91 1.97 53 La4O2(Re2O8) 2.41 2.57 69 (P1) (1.90 ± 1.93) (1.93 ± 2.02) (2.41) (2.54 ± 2.60) Cu5O2(VO4)2 1.94 1.98 54, 55 La4O(Mo2O10) 2.40 2.56 70 (1.90 ± 2.10) (1.89 ± 2.05) (2.39 ± 2.41) (2.37 ± 2.90) La3O2(ReO6) 2.39 2.60 71 M=Sn (C2) (2.32 ± 2.50) (2.24 ± 3.00) Sn2O(SO4) 2.23 2.42 56 La4O(Re6O18) 2.52 2.65 72 (2.14 ± 2.35) (2.23 ± 2.56) (2.52) (2.51 ± 2.93) Note.The space group is indicated for compounds existing in several polymorphic modifications. The table presents the average bond lengths and the limits of their variation (in brackets) in the crystal structure.The error in the determination of the bond lengths does not exceed 0.01A. 138 S V Krivovichev, S K Filatov, T F Semenovaalong the x axis and joined together into a layer parallel to the xz plane. The layers are combined into a framework via the Cu(1)O3Cl2 polyhedra. Thus, from the standpoint of traditional ideas, the most stable fragment in the structure of georgbokiite is a chain, parallel to the x axis, made up of edge-linked CuO4 squares.However, in the study of thermal deformations of georgbokiite it was found that the z and y axes are respectively the directions of minimum and maximum thermal expansions, the average expan- sion occurring along the x axis.73 Furthermore, one of the cleavage planes (yz) in the test compound is perpendicular to the direction of the CuO2 chains.Analysis of this structure from the standpoint of the crystal chemistry of oxocentred complexes showed that the `additional' oxygen atoms are tetrahedrally coordinated to copper atoms (Fig. 1b). By being alternately corner- and edge-linked, the [OCu4] groups form oxocentred [O2Cu5] chains extended parallel to the z axis (Fig. 2). The thermal expansion is a minimum precisely along this direction and both cleavage systems (xz and yz) are parallel to the latter. The maximum refractive index, corresponding as a rule to the direction of the densest rows of atoms, corresponds also to the direction of the z axis.74, 75 Thus the identification of oxocentred groups in the structures makes it possible to treat more clearly the anisotropy of the thermal expansion and of other physical properties of georgboki- ite than in the traditional approach.Henceforth, in numerating the ways in which the [OM4] groups can be linked together to form a cationic complex, we shall make use of polyhedral images similar to that presented in Fig. 2. Images of the structures from the point of view of the classical approach (Fig. 1) may be found in the original studies indicated in the references. III. Systematic treatment of cationic complexes based on [OM4] tetrahedra and the principles governing their descriptions In traditional crystal chemistry, [TO4] tetrahedra are as a rule corner-linked and one corner belongs to not more than two tetrahedra.76, 77 The linking together of the tetrahedra via their edges (let alone faces) is encountered very rarely.For example, edge-linking of the tetrahedra in silicate anions has been estab- lished in the fibrous modification of silicon dioxide 76 and in certain beryllosilicates.78 The formation of `knotted' linkages,77, 78 i.e. the linking together of several tetrahedra by one corner, is also an exceptional case and the `knot' consists as a rule of not more than four highly distorted tetrahedra.In describing the crystal structure using [OM4] tetrahedra, the possibility of their edge-linking is postulated and one M corner can belong to more than two tetrahedra. In the present review, oxocentred [OMx] complexes are represented as an assembly of [OM4] tetrahedra.There are several classifications of polyhedral structural units.76, 79, 80 The classification based on Liebau features,76 con- structed on the basis of a traditional systematic treatment of silicates devised by Machatschki, Bragg, etc., is the most general. The Liebau classification involves both different geometrical types of coordination polyhedra and various ways of linking them together (via corners, edges, and n-corner faces). However, it bears features of the structure of silicate anions, for the classification of which it has in fact been created.For a more complete classification of polyhedral edge-linked and face-linked structural units, this system requires a series of amplifications, which are unimportant for silicates. The principal characteristics of the systematic treatment employed are described briefly below and an account is given of the main principles governing this description of structures made up of oxocentred fragments.The problems of the classification of polyhedral structures have been described in greater detail in another communication.81 Features of the systematic treatment. 1. The coordination of the central atom is a parameter which includes both the coordi- nation number of the central atom and the geometry of the coordination polyhedron. The recommendations given by Parthe and coworkers 79, 80, 82 are employed in the determination of the values of the parameters.In particular, the designation 4t was adopted for tetrahedral groups. 2. The dimensionality of the complex D is the number of dimensions in which the complex is of infinite extent.The following values are possible: 0 (finite complexes), 1 (chain complexes), 2 (layered complexes), 3 (framework complexes). 3 and 4. The linkedness of the tetrahedra in the complex ML and the linkedness of the tetrahedron L. The parameter ML indicates the way in which it is possible to construct the specified complex by adding individual single poly- hedra.It is determined as the following hierarchical series of values: 3>2, 3>1, 2, 3>1, 3>2>1, 2>1>0. Here it is necessary to make use of Wells's rule: if an edge (or face) is shared by two tetrahedra, then its corners (and edges) are not considered to be shared by these two tetrahedra. The value of L reflects all the ways of linking together the polyhedra in the complex.The linkedness L is equal to the number of corner atoms shared by two coordination polyhedra:10 L=0 for an isolated polyhedron, L=1 for corner-linking, L=2 for edge-linking, and L=3 and above for face-linking. 5. The connectedness s of the polyhedra of a coordination polyhedron is equal to the number of polyhedra with which the given polyhedron shares corners, regardless of their linked- ness.76, 82 6.The branchedness of the complex B. The finite structural units and single chains { are called unbranched if they contain no subunits linked to more than two other subunits.82 Otherwise they are called branched. Furthermore, complex structural complexes, which may be regarded as made up of unbranched (branched) finite fragments or unbranched (branched) single chains, are described as unbranched (branched). The branchedness B of a cationic complex of infinite extent (i.e.withD>0) is a property of its fundamental chain. The fundamental chain is defined as the N0g y x Nm a33 a22 z [OCu4]6+ (SeO3)27 Cl Figure 2. The oxocentred [O2Cu5] chains in the structure of georgbokiite and the figure representing its thermal expansions.a22 and a33 are the axes of the figure representing the thermal expansion coefficients;N0 g andNm are the axes of the optical indicatrix in the yz plane. {A chain consisting of secondary tetrahedra is called single. Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic compounds 139chain from which the cationic complex may be constructed by its successive addition.82 The fundamental chain consists of a single chain (made up of only secondary polyhedra) and branches. Liebau 76 suggested that unbranched, open-branched, loop- branched, mixed-branched, and hybrid complexes, designated respectively by the symbols uB, oB, lB, olB, and hB, be distin- guished. 7. The periodicity P. The term periodicity of a structural fragment of infinite extent is the number of structural subunits (excluding branches) constituting the period of the chain from which this fragment may be constructed by the successive addition of subunits to one another.82 For finite ring complexes, the number of polyhedra constituting the ring is specified as the periodicity.Liebau 76 calls this parameter the ring periodicity. 8. The multiplicity M of the complex is the term given to the number of single polyhedra, chains, or layers, which, by linking to one another, form a complex with the same dimensionality as the initial complexes.82 9. The ratio n :m for the complex [AnBm], where A is the central atom and B is the ligand. Formula and diagram of connectedness.The following is the connectedness formula: (s : Ll7s1; L27s2...Ln7sn), where L1, L2, ..., Ln are specific values of linkedness, while s1, s2, ... sn are specific values of connectedness for the given polyhedron with others in accordance with the values of linkedness indicated ahead of them. The formula of the connectedness of this polyhedron shows how many polyhedra are linked to the given polyhedron and in what way.It is convenient to employ the so called diagram of connect- edness constructed on the basis of the Schlegel diagram for the given polyhedron. The latter represents a planar image of the edge network of any kind of convex polyhedron. For the tetrahedron, the Schlegel diagram represents the view from above on to a regular tetrahedron placed on one of its triangular bases.The Schlegel diagrams were first introduced into crystal chemistry by Hoppe and KoÈ hler.83 Henceforth we shall use the following ways of representing the elements of connectedness. 1. The corner designated by a circle links the given polyhedron to another. If the corner links the given polyhedron to more than one other polyhedron, then the number of such polyhedra is indicated next to the corner. 2. The edge identified by a semibold line is common to two polyhedra. The connectedness diagrams will be referred to as equivalent if the relative disposition of the linkage corners and/or edges in them is the same (or is mirror-symmetrical). Classification of the polyhedra in a polyhedral complex. For the crystal-chemical description of the coordination polyhedra, con- stituting the given complex it is necessary not only to indicate the geometrical characteristics but also to define the way in which they are joined together.Wells 84 ± 86 suggested that polyhedra with the same relative disposition as the elements of connectedness be referred to as topologically equivalent. Within the framework of the approach employed, this means that polyhedra with equiv- alent connectedness diagrams are referred to as topologically equivalent polyhedra in the complex. It is essential to note that the description of the disposition of the elements of connectedness in the polyhedron (with the aid of the connectedness diagram) is still insufficient to define the position of the polyhedron in the complex. In the same structure, topologically equivalent polyhedra may have different environ- ments comprising polyhedra with which they have common link- age corners. In such cases we speak of configurationally nonequivalent polyhedra (more rigorous definitions have been given elsewhere 81).Configurationally equivalent polyhedra are always topologi- cally equivalent, but topologically equivalent polyhedra may be configurationally nonequivalent.Crystallographically equivalent polyhedra are always topologically and configurationally equiv- alent. Thus, from this standpoint, a polyhedral cationic complex consists of n types of configurationally equivalent and m classes of topologically equivalent polyhedra. In the general case, we have m<n. The classification of the polyhedra in the structure is based on the order of hierarchical equivalence ratios: configurational ± topological ± crystallographic.Additional features of the systematic treatment. 10. The num- ber of configurational types of polyhedra in the complex and their ratio. 11 and 12. The diagrams and formulae of the connectedness of the configurational types of polyhedra.Crystal-chemical formulae. When the formula of the complex is written, the system recommended by Liebau et al.76, 82 is used to characterise it structurally. The following parameters are indi- cated in braces before the chemical formula of the complex written in square brackets: {B,MD ?}. The following designations are adopted for finite structures (D=0): {f} � for a chain of finite length, {r}�for a ring polyion, {c}�for a cage.79, 82 IV.Types of cationic [OM4] complexes 1. General remarks The structures of oxocentred complexes are described in terms of the [OM4] tetrahedra in accordance with the following main principles. Taking into account the features of the classification formulated in the previous section, the type units of oxocentred [OM4] structural units are treated systematically. All the known crystal structures in which the complex has been found are indicated for complexes of each type.Some of these structures are considered as examples and are described from the standpoint of the crystal chemistry of compounds with oxocentred groups. For convenience we introduced a numbering of the types of structural units within each dimensionality.A capital Latin letter is placed before the number of the complex indicating its dimen- sionality: I � finite (islands), C � one-dimensional or chain (chains), L � two-dimensional or layered (layers), F � three- dimensional or framework (frameworks). 2. Finite oxocentred complexes. Tables 2 and 3 as well as Fig. 3 present the main types of finite oxocentred complexes, the crystal structures in which these com- plexes have been found, and a topological description of the latter.I1. The individual [OM4] tetrahedron. The oxocentred [OM4] tetrahedron is known in organic crystal chemistry,28 ± 37 for example M=Cu, Be, or Zn. Among inorganic compounds, a single [OM4] tetrahedron can be identified, in particular, in the crystal structure of ponomarevite K4Cu4OCl10,87 ± 89 which con- Table 2.Classification of the types of finite oxocentred complexes based on the [OM4] tetrahedron. Num- L Para- n O:M Type of m p Connect- ber meter complex edness formula I 1 0 7 1 1 : 4 [OM4] 1 1 (0) I 2 1 {f } 2 2 : 7 {f }[O2M7] 1 1 (1: 1 ± 1) I3 1 {f } 4 4 : 3 {f }[O4M13] 2 A1 (1: 1 ± 1) B1 (2: 1 ± 2) I4 2 {f } 2 1 : 3 {f }[O2M6] 1 1 (1: 2 ± 1) I5 2 {f } 4 2 : 5 {f }[O4M10] 2 A1 (1: 2 ± 1) B1 (2: 2 ± 2) I6 2 {c} 4 1 : 2 {c}[O4M8] 1 1 (3: 2 ± 3) Note.The following designations have been adopn the subsequent tables: n=number of tetrahedra in the complex, m=number of topological types of tetrahedra in the complex, p=number of tetrahe- dra of the given topological type (A and B) in the complex. 140 S V Krivovichev, S K Filatov, T F Semenovatains tetranuclear clusters [Cu4OCl10] formed by oxygen as the central atom involved in tetrahedral coordination.I2. The binary group {f}[O2T7]. This oxocentred complex consists of two [OM4] tetrahedra linked by one common corner and it is therefore `reverse' analogue of the diorthosilicate group [Si2O7]. I3. The chain fragment {f} [O4M13] made up of four tetrahedra and discovered in the crystal structure of the compound Cu(Cu13O4)(SeO3)2Cl16.114 The fragment consists of four [OCu4] tetrahedra linked in succession via their corners.In the structure of the given compound, there are copper atoms which do not enter into the oxocentred tetrahedra. I4. The binary group {f} [O2M6] consists of two tetrahedra having one common edge.The presence of the complex [O2Cu6] having this structure has been established in the crystal structure of the exhalation mineral fedotovite K2Cu3O(SO4)3.46, 47 I5. We identified the chain fragment {f}[O4M10] with an edge- linkage made up of four tetrahedra in the crystal structure of Sr2Bi3V3O14 solved by Boje and MuÈ ller-Buschbaum.118 From the standpoint of the approach employed, the formula of this com- pound is written as Sr2Bi3O2(VO4)3.I6. An oxocentred complex made up of four [OM4] tetrahedra in which each tetrahedron is edge-linked to three others, was first noted by Keller in the compounds Pb9O4Br9 119 and TlPb8O4Br9.120 Later Riebe and Keller 121 noted that in a complex having this structure the M atoms not involved in the linking of the tetrahedra may be replaced by hydrogen.It is of interest that the complex [O4Pb4], having a similar structure but incorporating only Pb atoms participating in the linking of the tetrahedra, has been discovered in the gas phase,128, 129 while the complexes [(OH)4M4] (M=Mg, Co, Ni, Cd, Pb) have been found in aqueous solutions.130 ± 132 Table 4 presents the finite complexes formed from the com- plex I6 for different degrees of substitution n.Table 3. Finite oxocentred [OM4] complexes in the crystal structures of inorganic compounds. Num- Type Chemical Chemical Ref. ber of com- formula compound plex of complex I1 [OM4] [OCu4] K4Cu4OCl10 87 ± 89 (ponomarevite) Cu4(PO4)2O 49 ± 50 CuO(Cu,Mg)3(AsxP17xO4)2 90 (x=0.3) Cu4(AsO4)2O, P1 53 Cu4(AsO4)2O, Pnma 91 KCu5V3O13 92 Cu11O2(VO4)6 93 (fingerite) [OZn4] Zn4O(BO2)6 94 [OPb4] Pb4O(Pb2(BO3)3Cl) 95 Pb8Bi2(PO4)6O2 96 [OKBi3] K2Bi3(PO4)2O 97 [OYb4] Yb4OCl6 98 [OSm4] Sm4OCl6 99 [OEu4] Eu4OCl6 100 [OLa4] (La4O)(Re6O18) 72 La4Mo2O11 70 [OCa4] Ca4OCl6 101 Ca4(PO4)2O 102 [OFe4] Fe15Ge8O36 103 [OCe4] Ce4OS4Cl2 104 [OM4] M4OS4Cl2 105 (M= (M=La ± Nd) La ± Nd) I1 [OM4] [OLa2Ga2] La2ZnGa2S6O 106 [OCaLaGa2] CaLaGa3S6O 106 [OSrLaGa2] SrLaGa3S6O 106 [OSr2Ge2] Sr2ZnGe2S6O 106 I2 {f }[O2M7] [O2Pb7] Pb9Al8O21 107 Pb9Ga8O21 108, 109 [O2Pb6Sb] Pb6Cu4AlSbO2(OH)16Cl4 . 110 . (SO4)2 (mammothite) [O2Cu7] Cu9O2(PO4)4(OH)2 111 [O2TiFe3Ba3] Ba4Fe3Ti(B2Si8O27)O2Cl0.89 112, 113 (taramellite) I3 {f }[O4M13] [O4Cu13] Cu(Cu13O4)(SeO3)2Cl16 114 I4 {f }[O2M6] [O2Zn6] Zn4V2O9 115 [O2Pb6] Pb3MO12F2 (M=Nb, Ma) 116 [O2Fe6] Fe3.2Ge1.8O8 117 [O2Cu6] K2Cu3O(SO4)3 46, 47 (fedotovite) NaKCu3O(SO4)3 45 (euchlorine) Cu4O(SeO3)3-I,II 51 I5 {f }[O4M10] [O4Sr4Bi6] Sr2Bi3V3O14 118 I6 {c}[O4M8] [O4Pb8] Pb9O4Br9 119 TlPb8O4Br9 120 [O4Sn8] Sn2O(SO4) 56 Table 4.Finite oxocentred complexes formed from complex I6 as a result of the substitution n(O+M) ? n(OH). n Type of Chemical Chemical Ref.complex formula compound of complex 0 {c}[O4M8] [O4Pb8] Pb9O4Br9 119 TlPb8O4Br9 120 [O4Sn8] Sn2O(SO4) 56 1 {c}[O3(OH)M7] [O3(OH)Sn7] Sn21Cl16(OH)14O6 122, 123 2 {c}[O2(OH)2M6] [O2(OH)2Pb4Hg2] HgPb2O(OH)Br3 121 4 {c}[(OH)4M4] [(OH)4Pb4] Pb4(OH)4(ClO4)4 .2H2O 124 [Pb4(OH)4]3(CO3)(ClO4)10 . . 2H2O 125 [(O,OH)4Pb4] Pb7Ca2Al12Si36(O,OH)100 . 126, .m(H2O,OH) 127 I 1 I 2 I 3 A B A B I4 A B A B I5 I6 Figure 3.The types of finite oxocentred complexes. A, B�tetrahedra belonging to different topological types. Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic compounds 1413. Oxocentred chain complexes Oxocentred chains can be conveniently classified in terms of the types of single chains from which they are constructed.The linking of single chains leads to the formation of multiple structural units. All the oxocentred chains can be divided into families in terms of their multiplicity and linkedness. Tables 5 and 6 present the types of oxocentred chain complexes based on the [OM4] tetrahedra and the chemical compounds in the structures of which such com- plexes have been found. C1.The single-period chain {uB, 11 ?}[OM3] (Fig. 4). In this chain, the tetrahedra are linked only via the corners with a periodicity 1. This polyion is an analogue of the metagermanate chain [GeO3]. C2. The {uB, 21 ?}[O2M5] double chain. The linking of two C1 chains via free corners leads to the formation of the C2 double chain. Such a fragment can be identified in chemical compounds belonging to the ludwigite structural type.In the crystal structures of these compounds, there is also an `additional' oxygen atom with a tetragonal-pyramidal coordination, as well as metal atoms which do not enter into the tetrahedral oxocentred complex. C3. The {uB, 21 ?}[OM2] double chain. The linking of two C1 chains to one another via the edges leads to the formation of a type C3 oxocentred chain.The main type of linkedness ML for this double chain is 2, although for the fundamental chain ML=1. The C3 chain may be identified in oxoborates with the warwickite structural type. In contrast to ludwigite, in the warwickite structural type all the `additional' oxygen atoms are involved in tetrahedral coordination and all the metal atoms enter into the oxocentred complex.Chains of analogous structure have been found in the structures of the diorthosilicates of the cuspidine and epistolite groups (innelite, lomonosovite, murmanite, etc.). In such compounds, the `additional' oxygen, not entering into anionic complexes, may be substituted by fluorine with its similar properties. The nature of the substitution can be both statistical and ordered.The structural similarity of oxoborates and the cuspidine-group diorthosilicates was first pointed out by Belov.77 C4. The {uB, 31 ?}[O3M5] triple chain. As a result of the addition of yet another single C1 chain to a C3 chain, a triple oxocentred C4 chain is formed. Such a chain was first identified by Carre et al.20 in the crystal structure of In6La10O6S17.180 The C1, C3, and C4 chains may be assigned to a single family with the general formula {uB, n1 ?}[OnMn+2], where n is the multiplicity of the chain.C5. The {uB, 11 ?}[O2M6] single chain. This chain is topolog- ically equivalent to the C1 chain, different from the latter by the periodicity (P=2). In terms of its structure, the C5 chain is a reverse analogue of the pyroxene chain in the silicate.The differ- ence consists in the fact that the corners not involved in the linking of the tetrahedra into the C5 chain are turned in opposite directions relative to the plane of the chain, whereas in pyroxenes they are turned in one direction. A C5 complex has been detected, in particular, in the crystal structure of the exhalation mineral kamchatkite KCu3O(SO4)2Cl (Fig. 5).43, 44 C6. The {uB, 21 ?}[O2M5] double chain consists of two edge- linked C5 chains. A complex with this structure may be identified in stoiberite Cu5O2(VO4)2,54, 55 the structure of which was not previously considered in terms of this aspect. C1 C3 C5 C2 C4 A A B B C6 2 A A B B Figure 4. The types of oxocentred chain complexes (C1 ±C6). A, B�tetrahedra belonging to different topological types.Table 5. Classification of the types of oxocentred chain complexes based on the [OM4l tetrahedron. Num- ML L P B M O: T n m p Connectedness ber formula �1 1 1 1 uB 1 1 : 3 1 1 1 (2: 1 ± 2) C2 1 1 1 uB 2 2 : 5 1 1 1 (3: 1 ± 3) C3 2 1,B 2 1 : 2 1 1 1 (4: 1 ± 2; 2 ± 2) C4 2 1, 2 1 uB 3 3 : 5 2 2 A2 (5: 1 ± 3; 2 ± 2) B1 (6: 1 ± 2; 2 ± 4) C5 1 1 2 uB 1 1 : 3 1 1 1 (2: 1 ± 2) C6 1, 2 1, 2 2 uB 2 2 : 5 2 2 A1 (3: 1 ± 3) B1 (4: 1 ± 3; 2 ± 1) C7 2 2 2 uB 1 1 : 2 1 1 1 (2: 2 ± 2) C8 2 1, 2 2 uB 2 2 : 3 1 1 1 (5: 1 ± 2; 2 ± 3) C9 2 1, 2 2 uB 3 3 : 4 2 2 A1 (5: 1 ± 2; 2 ± 3) B2 (8: 1 ± 4; 2 ± 4) C10 2 1, 2 2 uB 6 6 : 7 3 3 A1 (7: 1 ± 4; 2 ± 3) B1 (9: 1 ± 6; 2 ± 3) C1 (13: 1 ± 8; 2 ± 5) C11 2 1, 2 2 uB 6 6 : 7 5 4 A1 (5: 1 ± 2; 2 ± 3) B1 (12: 1 ± 8; 2 ± 4) C2 (9: 1 ± 6; 2 ± 3) D1 (18: 1 ± 12; 2 ± 6) E1 (9: 1 ± 6; 2 ± 3) C12 1, 2 1, 2 2 uB 1 2 : 5 1 1 1 (2: 1 ± 1; 2 ± 1) C13 1, 2 1, 2 2 uB 2 1 : 2 2 2 A1 (3: 1 ± 2; 2 ± 1) B1 (4: 1 ± 2; 2 ± 2) C14 1, 2 1, 2 4 uB 1 2 : 5 1 1 1 (2: 1 ± 1; 2 ± 1) C15 1, 2 1, 2 6 uB 1 3 : 8 2 2 A1 (2: 1 ± 2) B2 (2: 1 ± 1; 2 ± 1) C16 1 1 1 lB 2 1 : 2 3 3 A1 (4: 1 ± 1; 2 ± 3) B2 (3: 1 ± 2; 2 ± 1) C1 (4: 1 ± 3; 2 ± 1) (SO4)27 Cl7 [O2Cu6]8+ K+ z x y Figure 5. The crystal structure of kamchatkite KCu3O(SO4)2Cl. 142 S V Krivovichev, S K Filatov, T F SemenovaTable 6. Oxocentred [OM4] chain complexes in the crystal structures of inorganic compounds. Number Type of complex Chemical formula of complex Chemical compound Ref. �1 {uB, 11 1}[OM3] [OPb3] Pb3Ta5O9F13 (Pb3O(Ta5O8)F13) 133 [OY3] Y3OCl2(OH)5 134 [OGd3] Gd3O(OH)5Br2 135 [OCu2Zn] Cu2Zn(B2O5)O 136 [OCu2Cd] Cu2Cd(B2O5)O 137 [OCu2Co] Cu2Co(B2O5)O 138 C2 {uB, 21 1}[O2M5] [O2M5] (M=Fe, Mg, Ti, Sb, Sn, (Mg,Fe2+)2Fe3+O2(BO3) (ludwigite) 139 ± 143 Ni, Cr, Mn, Al, Mo, Zn Fe3O2(BO3) (vonsenite) 144, 145 Mg1.7Mn1.29O2(BO3) (takeuchiite) 146 (Mg,Mn)2(Mn,Fe)O2(BO3) (orthopinakiolite) 147 (Sn,Fe,Mg)(Fe,Mg)2O2(BO3) (hulsite) 148, 149 Ni2CrO2(BO3) 140 Ni2VO2(BO3) 140 Ni2MO2(BO3) (M=Ga, Fe,Al, Cr) 150 Ni2FeO2(BO3) 151 Mg2MnO2(BO3) (fredrikssonite) 152 Zn5Mn(BO3)2O4 153 C3 {uB, 21 1}[OM2] [OLa2] (La2O)(LaGaS5) 154 [OPb2] Pb11Si3O17 155 Pb11Ge3O17 156 [OLaCr] LaCrOS2 157 [OY2] Y2O(BeO3) 158, 159 [OFe2] Fe2O(BO3) 160 [OFeCo] FeCoO(BO3) 158 [OMg1.5Ti0.5] Mg(Mg0.5Ti0.5)O(BO3) (warwickite) 161 ± 163 [OMn2] Mn2O(BO3) 164 [OMnFe] MnFeO(BO3) 165 [OMn(Al,Y)] MnAl0.5Y0.5O(BO3) 165 [OCo1.5M0.5] (M=Ti, Zr) Co1.5M0.5O(BO3) (M=Ti, Zr) 166 [OZnFe] ZnFeO(BO3) 153 [OTiNa] Na5Ti2(Si2O7)(PO4)O2 (lomonosovite, 167 ± 170 b-lomonosovite) Na2Ti2(Si2O7)O2 (murmanite) 171, 172 [O3FCa7Nb] Ca7Nb(Si2O7)2O3F (niocalite) 173, 174 [(O,F)2Ca2NaZr] Ca2Na(Zr,Nb)(Si2O7)(O,F)2 (woehlerite) 175 [(OH,F)Ca2] Ca4(Si2O7)(OH,F)2 (cuspidine) 176, 177 [OF(Na,Ca)3Zr] (Na,Ca,Mn)3(Zr,Ti)(Si2O7)OF (lavenite) 178, 179 C4 {uB, 31 1}[O3M5] [O3La5] In6La10O6S17 180 C5 {uB, 11 1}[O2M6] [O2Cu6] KCu3O(SO4)2Cl (kamchatkite) 43, 44 Cu3V2O8(H2O) 181 Cu8ZnO2(SeO3)4Cl6 182 Cu3Mo2O9 183, 184 Na2Cu(Cu3O)(PO4)2Cl 48 [O2Zn6] Zn3O(SO4) 185 [O2Ti2Y4] Y2(Y2TiO)(SiO4)2F6 186 C6 {uB, 21 1}[O2M5] [O2Cu5] Cu5V2O10 (stoiberite) 54, 55 C7 {uB, 11 1}[OM2] [OPb2] Pb2OFX (X=Cl, Br, I) 187 Pb2O(SO4 (lanarkite) 22 Pb2O(WO4) 188 Pb2O(CrO4) (phoenicochroite) 64 ± 66 Pb2O(XO4) (X=S, Cr, Mo) 66 [O2Cu3(Al,Fe)] K3Cu3(Al,Fe)O2(SO4)2 (kljuchevskite) 189, 190 [O2Cu3Al] K3Cu3AlO2(SO4)2 (alumokljuchevskite) 191 [OCu2] K2Cu2O(SO4) (piypite) 192, 193 Cu4O2(VO4)Cl 194 [OBi2] (UO2)Bi4O4(AsO4)2 .2H2O (walpurgite, 195 ± 197 orthowalpurgite) [OPbGe] PbGeO(Ge2O6) 198 [OCaBi] CaBiVO5 199 [OLa2] La4Re2O10 69 [ONd2] Nd4Re2O11 200 [O2Pr4] Na2(Pr4O2)Cl9 201 Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic compounds 143C7.The {uB, 11 ?}[OM2] fundamental chain (Fig. 6). A single oxocentred chain, consisting of secondary tetrahedra edge-linked in succession, was first identified by Sahl 22 in the crystal structure of lanarkite Pb2O(SO4). This one-dimensional structural unit based on [OM4] tetrahedra is one of the commonest in oxocentred complexes.Thus it has been detected in three new minerals of exhalation origin in the Tolbachick volcano: klyuchevskite,189, 190 alumoklyuchevskite,191 and piypite.192, 193 C8. The {uB, 21 ?}[O2M3] double chain. The edge-linking of two C7 chains leads to the formation of the C8 double chain. C9.The {uB, 31 ?}[O3M4] triple chain is formed by the linking of three C7 chains. A similar complex with the formula [O3La4] has been identified by Carre et al.20 in the crystal structure of La4O3As3S9.211 The C7, C8, and C9 chains form a family with the general formula {uB, n1 ?}[OnMn+1], where n is the multiplicity of the chain.It may be postulated that a chain belonging to the same family with n=4 occurs in the crystal structure of Pb5O4[SO4], which could not be fully solved. This hypothesis is based on the existence of oxocentred chains of type C7 (n=1) and C8 (n=2) in the compounds Pb2O(SO4) 22 and Pb3O2(SO4) 57 ± 60 respec- tively, which have similar compositions.C10, C11. The six-fold chains having the general formula {uB, 61 ?}[O6M7] consist of six type C7 chains linked in different ways. The possibility of identifying the C10 polyion in the Bi14O16(SO4)5 structure and of representing it by a block cut out of a type PbO layer was pointed out by Aurivillius.212 The C11 chain may be identified in the structure of the high-temperature modification of bismuth oxomolybdate g-Bi2MoO6 tentatively determined on the basis of high-resolution electron microscopy data.213 The differ- ence between the C10 and C11 chains is reflected in the configura- tional and topological properties of the tetrahedra constituting Table 6 (continued).Number Type of complex Chemical formula of complex Chemical compound Ref. �8 {uB, 21 1}[O2M3] [O2Pb3] Pb3O2(SO4) (P21/m) 57, 58 Pb3O2(SO4) (Cmcm) 59 Pb3O2(SO4) (P1) 60 Pb3O2Cl2 (mendipite) 202, 203 Pb3O2I2 204 Pb3CuO2(OH)2Cl2 (chloroxiphite) 205 [O2BiMg2] BiMg2O2(PO4) 206 BiMg2O2(AsO4) [O2La3] La3O2(ReO6) (P21/m) 68 La3O2(ReO6) (C2) 69 [O2Y3] Y3O2(ReO6) 207 [O2Sm3] Sm3O2(ReO6) 208 [O2Ce2Ti] Na2Ce2TiO2(SiO4)(CO3)2 (tundrite) 209, 210 C9 {uB, 31 1}[O3M4] [O3La4] La4O3(AsS3)2 211 C10 {uB, 61 1}[O6M7] [O6Bi7] Bi14O16(SO4)5 212 C11 {uB, 61 1}[O6M7] [O6Bi7] g-Bi2MoO6 213 C12 {uB, 11 1}[O2M5] [O2Cu5] Cu2O5(SeO3)2Cl2 42 Cu5O2(PO4) 52 [O2M5] (M=Pb, Ge, Pb3GeGa10O20 214 Ga, Ba, Al, Sn, Fe, Ti Ba3SnFe10O20 214 Pb3GeAl10O20 215 Pb3SiAl10O20 215 Ba3TiAl10O20 216 BaSrPbMn2Al9O20 217 C13 {uB, 21 1}[OM3] [OAl2] Al2O(SiO4) (kyanite) 218, 219 [OFe2] Fe2O(GeO4) 220 C14 {uB, 11 1}[O2M5] [O2(Mg,Fe)5] Na2(Mg,Fe)6[(Ge,Fe)6O18]O2 221 [O2(Mg,Cr)5] NaMg2Cr(Si3O9)O (krinovite) 222 [O2(Mg,Al)5] Ca2(Mg,Al)6O2[(Si,Al,B)6O18] (serendibite) 223 ± 225 [O2(Fe,Ti)5] Na2Fe5TiO2(Si6O18) (aenigmatite) 226 [O2(Mg,Ti,Al,Fe)5] Ca2(Mg,Ti,Al,Fe)6O2(Si6O18) (rhoenite) 227 (Ca,Na)2(Mg,Al,Fe)6O[(Si,Al,Be)6O18] 228 (makarochkinite) C15 {uB, 11 1}[O3M8] [O3Pb8] Pb8Cu(AsO3)2O3Cl5 (freedite) 67, 229 C16 {lB, 21 1}[OM2] [O3Cu4Ti2] Cu9Ti(B2O5)(BO3)2O6 230 C7 C8 C9 A B A B C10 A B C 3 3 B 3 A 2 2 2 C A B C D E C11 A, B C D E 3 3 3 3 2 2 Figure 6.The types of oxocentred chain complexes (C7 ±C11). A, B, C, D, E�tetrahedra belonging to different topological types. 144 S V Krivovichev, S K Filatov, T F Semenovathem. There are three configurational types of tetrahedra in the C10 polyion, each of which constitutes a topological equivalence class.The C11 chain consists of tetrahedra with five different configurations, two of which are of the same topological type. The example of these chains shows that the use of the configurational and topological properties of the tetrahedra is important for the classification of structural units.C12. The {uB, 11 ?}[O2M5] single chain (Fig. 7). In this chain, links via corners and edges alternate. An example of a compound with such a chain is provided by georgbokiite Cu5O2(SeO3)2Cl2 (in the original study,42 the coordination of the additional oxygen atom was not considered). C13. The {uB, 21 ?}[OM2] double chain, consisting of two type C12 chain first identified by Bergerhoff and Paeslack 19 in kyanite Al2O(SiO4).218 C14.The oxocentred {uB, 11 ?}[O2M5] chain, which may be found in compounds of the aenigmatite structural type, is a topological analogue of the C12 chain but with a periodicity of 4.221 ± 228 C15. The {uB, 11 ?}[O6M16] single chain with a periodicity of 6 is an interesting example of the alternation of two bonds via neighbouring corners with a single bond via the edge.This remarkable polyion, with the formula [O3Pb8], may be identified in the structure of freedite Pb8Cu(AsO3)2O3Cl5, solved by Per- tlik,67 who did not, however, consider it within the framework of the approach which we are employing. C16. The {lB, 11 ?}[OM2] loop-branched chain has been detected in the structure of copper titanium oxoborate Cu9Ti(B205)2(BO3)2O6.This consists of two types of C1 chains linked by two additional tetrahedra adjoining them via two edges each. It is essential to note that this compound contains also `additional' oxygen atoms involved in nontetrahedral (ternary) coordination and copper atoms which do not enter into the complex under consideration. The C16 chain is the only example of a branched complex involving oxocentred chains. 4. Layered oxocentred complexes A series of layers may be described as derivative of the type PbO tetrahedral layer. Carre et al.20 suggested that certain chains based on the [OLa4] tetrahedron be also considered in terms of this aspect. However, the above principle is subject to limitations, since there are many structural units which cannot be detected among derivatives of the PbO layer regardless of the way in which it is `sliced'.We therefore use this approach only for certain layered structures. Tables 7 and 8 present the characteristics of the types of layered oxocentred complexes based on [OM4] tetrahedra and the chemical compounds in the structures of which these complexes have been detected.L1. The {uB, 12 ?}[O2M5] layer (Fig. 8) can be regarded as made up of C5 single chains. In terms of its structure, it resembles the [Si2O5] tetrahedral networks constituting (together with octahedral networks) the structures of layered silicates.76 How- ever, the topological structures of the layer considered and the silicate layer differ, since the unshared corners of neighbouring tetrahedra in the L1 layer are turned in opposite directions relative to the plane of the layer.The difference between the silicate tetrahedral network and the L1 layer is analogous to the differ- ence between the pyroxene chain and the C5 chain. The structural unit [O2Cu5] of the L1 type has been detected in the crystal structure of averievite [Cu5O2](VO4)2 . MCl (M=K, Rb, Cs) (Fig. 9).232, 233 In this structure, the oxocentred layers are located exactly one under the other, the [VO4] groups are `glued' to the Table 7. Classification of the types of oxocentred layered complexes based on the [OM4] tetrahedron. Num- ML L P B M O: T m n p Connectedness ber formula L1 1 1 2 uB 1 2 : 5 1 1 1 (3: 1 ± 3) L2 1 1 2 uB 1 2 : 5 1 1 1 (3: 1 ± 3) L3 2 1, 2 1 uB 2 1 : 1 1 1 1 (9: 1 ± 6; 2 ± 3) L4 2 1, 2 1 uB 4 4 : 3 2 2 A1 (13: 1 ± 10; 2 ± 3) B1 (18: 1 ± 12; 2 ± 6) L5 1, 2 1, 2 2 uB 1 4 : 5 1 1 1 (7: 1 ± 4; 2 ± 3) L6 1, 2 1, 2 2 uB 1 6 : 7 2 2 A1 (7: 1 ± 4; 2 ± 3) B1 (8: 1 ± 4; 2 ± 4) L7 1, 2 1, 2 2 uB 1 8 : 9 2 2 A1 (7: 1 ± 4; 2 ± 3) B1 (8: 1 ± 4; 2 ± 4) L8 1, 2 1, 2 4 lB 1 1 : 2 1 1 1 (5: 1 ± 4; 2 ± 1) L9 1, 2 1, 2 4 uB 1 2 : 3 1 1 1 (5: 1 ± 3; 2 ± 2) L10 1, 2 1, 2 2 uB 1 1 : 2 1 1 1 (3: 1 ± 2; 2 ± 1) L11 1, 2 1, 2 2 uB 1 1 : 2 1 1 1 (6: 1 ± 5; 2 ± 1) L12 2 1, 2 2 uB 1 1 : 1 1 1 1 (8: 1 ± 4; 2 ± 4) L13 2 1, 2 4 uB 1 1 : 1 1 1 1 (8: 1 ± 4; 2 ± 4) L14 2 1, 2 3 lB 1 4 : 5 1 1 1 (6: 1 ± 3; 2 ± 3) L15 1, 2 1, 2 4 lB 1 3 : 5 2 2 A2 (4: 1 ± 2; 2 ± 2) B1 (5: 1 ± 2; 2 ± 3) L16 2 1, 2 2 lB 1 9 : 14 6 4 A1 (4: 1 ± 2; 2 ± 2) B1 (4: 1 ± 2; 2 ± 2) C1 (5: 1 ± 2; 2 ± 3) D1 (5: 1 ± 2; 2 ± 3) E1 (5: 1 ± 3; 2 ± 2) F1 (6: 1 ± 2; 2 ± 4) L17 2 1, 2 2 lB 1 7 : 8 5 3 A2 (7: 1 ± 4; 2 ± 3) B2 (7: 1 ± 4; 2 ± 3) C1 (6: 1 ± 2; 2 ± 4) D1 (7: 1 ± 3; 2 ± 4) E1 (7: 1 ± 3; 2 ± 4) L18 1, 2 1, 2 2 hB 1 11 : 12 5 5 A2 (9: 1 ± 4; 2 ± 5) B4 (11: 1 ± 8; 2 ± 3) C1 (12: 1 ± 8; 2 ± 4) D2 (8: 1 ± 8) E2 (9: 1 ± 8; 2 ± 1) L19 1, 2 1, 2 2 lB 1 4 : 7 5 5 A1 (4; 1 ± 2; 2 ± 2) B1 (4: 1 ± 2; 2 ± 2) C1 (3: 1 ± 1; 2 ± 2) D1 (4: 1 ± 3; 2 ± 1) E1 (4: 1 ± 2; 2 ± 2) L20 2 1, 2 2 uB 2 4 : 3 1 1 1 (15: 1 ± 10; 2 ± 5) C14 A B A B C15 B C A A B C C16 C12 C13 B A A B Figure 7.The types of oxocentred chain complexes (C12 ±C16). A, B, C�tetrahedra belonging to different topological types. Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic compounds 145bases of the [OCu4] tetrahedra and together with the layers form the fundamental electrically neutral Cu5O2(VO4)2 framework.As a consequence of the disposition of the layers one under the other, broad cavities with a radius in excess of 3.0 A, which incorporate the alkali metal ions K+, Rb+, and Cs+ as well as the chloride ions Cl7, are formed in the structure.L2. A layer of this type is a `corrugated' analogue of the L1 layer. It is distorted in such a way that the periodicity of the fundamental chain of the layer changes from 2 to 3. This layer has been detected by Shuvalov et al.234 in the crystal structure of NaCu5O2(SeO3)2Cl3. L3. The oxocentred {uB, 22 ?}[OM] layer with the chemical formula [OLa] was identified by Bergerhoff and Paeslack 19 in the La2O2S structure solved by Zachariasen.235 The multiplicity of this layer is 2, although it can be regarded as consisting of two corner-linked layers with a periodicity of 1.L4. The [O4M3] structural unit of this type consists of two L3 layers `glued' to one another or of four simple corner-linked single-period layers. As a result of the `glueing', the O:M ratio becomes 1.333, i.e.greater than 1. L5, L6, L7. The layers of these types can be regarded as a result of the successive linking of C7 chains. The C7 chains are initially linked via their edges into multiple chains similar to C8 and C9, Table 8. Oxocentred [OM4] layered complexes in the crystal structures of inorganic compounds.Number Type of complex Chemical formula of complex Chemical compound Ref. L1 {uB, 12 1}[O2M5] [O2Cu3Pb2] Pb2Cu3O2(NO3)2(SeO3)2 231 [O2Cu5] Cu5O2(VO4)2 .MCl (M=K, Rb, Cs) (averievite) 232, 233 L2 {uB, 12 1}[O2M5] [O2Cu5] NaCu5O3(SeO3)2Cl3 234 L3 {uB, 22 1}[OM] [OX] (X=La, Ce, Pu) La2O2S, Ce2O2S, Pu2O2S 235 La2O2Se 236 LaOF 237 L4 {uB, 12 1}[O4M3] [O4(Bi,Sr)3] Bi0.765Sr0.235O1.383 238 L5 {uB, 12 1}[O4M5] [O4Cu3Bi2] Na2[(Bi2Cu3O4(AsO4)2] .H2O 239 K2[Bi2Cu3O4(AsO4)2] .2H2O 239 L6 {uB, 12 1}[O6M7] [O6Cu3Bi4] Cu3Bi4V2O14 240 L7 {uB, 12 1}[O8M9] [O8Bi9] Bi20O27(SO4)12 212 L8 {uB, 12 1}[OM2] [OY2] Y2OS2 241 L9 {uB, 12 1}[O2M3] [O2Ce2Cr] (Ce2CrO2)CrS4 242 [O2HgPb2] HgPb2O2Cl2 243 L10 {uB, 12 1}[OM2] [OCu2] Cu2O(SO4) (dolerophanite) 23, 24 [O2Cu3Bi] Cu3Bi(SeO3)2O2Cl (francisite) 244 L11 {uB, 12 1}[OM3] [O(Mg,Mn)2] (Mg,Mn)2Mn(BO3)2 142, 245 [(O,F)4(Ca,Na)6ZrTi] Ca3.5Na2.5Zr(Ti,Mn,Nb)(Si2O7)2 .F2O(F,O) 246 (rosenbuschite) [(O,F)2(Na,Ca,Ce)3Ti] (Na,Ca,Ce)3Ti(Se2O7)(O,F)2 (mosandrite) 247 [(O,F)2(Na,Ca)2(Zr,Ti,Mn)2] (Na,Ca)2(Zr,Ti,Mn)2(Si2O7)(O,F)2 (seidozerite) 248, 249 [O4Ti3CaBa4] Na2Ba3(Ba,K,Mn)(Ca,Na)Ti(TiO2)2 250 [Si2O7]2(SO4)2 (innelite) [(O,F)4(Ti,Al)2(Ca,Na)6] (Ca,Na)7(Ti,Al)2(Si2O7)2O(O,F)3 (goetzenite) 251 L12 {uB, 12 1}[OM] [OPb] PbO, P4/nmm 252 PbO, Cmma 252 Pb7O8Cl2 (asisite) 253 [OFe] FeO(OH) (lepidocrocite) 254 [OAl] AlO(OH) (boehmite) 255 [O3Bi2Co] Bi2CoO3SO4 256 [O2PbBi] PbBiO2Cl (perite) 257, 258 [O2PbSb] PbSbO2Cl (nadorite) 25[OM] (M=Bi, Nd, Gd, Dy) (MO)(CuSe) (M=Bi, Nd, Gd, Dy) 260 [(O,OH)4Pb3(Sb,As)] Pb3Sb0.6As0.4(O3OH)Cl2 (thorikosite) 261 [(O,OH)2Pb2] Pb2(O,OH)2Cl (blixite) 261 [OBi] Bi2O2(CO3) (bismutite) 262 CaBi2O2(CO3)2 (bayerite) 262 BiOF (zavaritskite) 263, 264 BiOCl (bismoclite) 265 Bi2O2(MoO4) (koehlinite) 266 ± 268 Bi2O2(WO4) (russellite) 269 CaBiOF(CO3) (kettnerite) 270 L13 {uB, 12 1}[OM] [OPb] PbO, Pbcm 271 L14 {lB, 12 1}[O4M5] [O4Pb4Ag] AgPb4O4Cl 272 L15 {lB, 12 1}[O3M5] [O3Pb5] Pb5O3(GeO4) 61 L16 {lB, 12 1}[O9M14] [O9Pb14] Pb14(VO4)2O9Cl4 (kombatite) 62, 63 Pb14(AsO4)2O9Cl4 (salinite) 273 L17 {lB, 12 1}[O7M8] [O7Pb8] Ag2Pb8O7Cl4 274 L18 {hB, 12 1}[O11M12] [O8F3(Ca,Na)8(Ti,Nb)4] (Ca,Na)8(Ti,Nb)4(Si2O7)2O8F3 (fersmanite) 275 L19 {lB, 12 1}[O4M7] [O4Pb7] Pb11Si3O17 155 Pb11Ge3O17 156 L20 {uB, 22 1}[O4M3] [O4Ba2Bi] BaBi4O4I2 276 146 S V Krivovichev, S K Filatov, T F Semenovaafter which these multiple chains are linked via lateral corners into infinite layers. Thus the L5 and L6 layers can be regarded as consisting of C8 and C9 chains respectively. The L7 layer is formed from a C7 four-fold chain, the individual fragments of which have not so far been detected in chemical compounds.The possibility of identifying the L7 layer in the Bi26O27(SO4)12 crystal structure has been pointed out.212 The L5 and L6 layers were not considered in the original studies.It is of interest that the last two layers in compounds have similar chemical compositions � [O4Cu3Bi2] and [O6Cu3Bi4] respectively. In these complexes, the Bi atoms participate only in the edge-linking of the C7 chains into multiple chains, whereas the Cu atoms are involved in corner- linking into a layer of the multiple fragments formed.Thus the functions of the cations in the topological structures of the L5 and L6 layers are different. L8. The {uB, 12 ?}[OM2] layer may be regarded as consisting of finite I4 complexes. L9. A type L9 layer was first described by Keller and Langer 243 in the structure of HgPb2O2Cl2.The layer is made up of C3 chains by the linking of the latter via the corners of the tetrahedra not involved in edge-linking. L10.A{uB, 12 ?}[OM2] layer has been noted by Bergerhoff and Paeslack 19 in the crystal structure of dolerophanite Cu2O(SO4). This layer can also be identified in the structure of francisite 244 (Pring et al.244 did not consider the structure of the oxocentred layer).L11. A type L11 layer may be found in the crystal structure of pinakiolite (Mg, Mn)2Mn3+(BO3)O2. Together with the tetrahe- drally coordinated `additional' oxygen atoms, pinakiolite con- tains `additional' oxygen atoms with the [4+1] coordination�a `tetragonal pyramid' � as well as metal atoms not involved in the oxocentred groups. On the other hand, all the `additional' oxygen atoms in the structures of a series of diorthosilicates belonging to the mosandrite ± rosenbuschite group 246 ± 251 are involved in tetrahedral coordination, while all the cations (with the exception of innelite and goetzenite) participate in the for- mation of the oxocentred tetrahedra.As in the case of the structures of the cuspidine series (with a C3 chain), the central oxygen atom in the [OM4] tetrahedra is partly substituted by fluorine, which does not disturb the overall structure of the complex.L12. The [OM] layer. The [OM] layer is one of the commonest layers with edge-linking of tetrahedral complexes. For example, in the case of lead monoxide [tetragonal and one of the orthorhom- bic (Cmma) modifications], the [OPb] layer is made up of [OPb4] tetrahedra.252 An oxocentred layer of this type has been detected in the structures of a multiplicity of chemical compounds (see a review 277 as well as Table 8). L13.The layer in the orthorhombic (Pbcm) PbO 271 differs structurally from L12 by the marked `corrugations' of the PbO layers. The topological structures of these layers are also different, although their constituent [OPb4] tetrahedra are topologically equivalent.L14, L15 (Fig. 10), L16. These layers can be readily obtained by `cutting out' different blocks of OPb4 tetrahedra from the tetragonal PbO layer. In AgPb4O4Cl,272 one tetrahedron is `cut out' in each case, whereas in Pb5O3(GeO4)61 blocks of six tetrahedra (three by two in size) are `cut out'. In the komba- tite 62, 63 and sahlinite 273 structures, `butterflies' consisting of seven [OPb4] tetrahedra are `cut out'.In the layers formed after `cutting out', the symmetry of the [OPb4] is distorted as a consequence of the removal of neighbouring tetrahedra. L17. The [O7Pb8] layer of this type is a highly `corrugated' version of the L12 and L13 layers, where individual [OPb4] tetrahedra have been `cut out'.The O:M ratio in such a layer is 7 : 8. L18. The oxofluorocentred [O8F3(Ca, Na)8(Ti, Nb)4] layer, made up of a defective (with one-tetrahedron `cut out') L12 layer to which single type C1 chains have been added from above and from below, may be identified in the crystal structure of the mineral fersmanite.275 The addition takes place in such a way that the direction of theC1 chain from the upper side of the layer is perpendicular to the direction of the same chain from the lower side.Each second tetrahedron of the chain is then located above or below the `cut out' in the main layer. The [Si2O7] diorthosilicate groups are located between the layers having this structure in fersmanite. In the original study,275 the oxocentred complexes were not identified.L19.Alayer of this type is made up of three-period chains with alternation: two linkages via the edges and one linkage via a corner. Such chains are loop-branched, since they are connected by two additional tetrahedra. L1 L2 Figure 8. The types of oxocentred layered complexes L1 and L2. MCl [O2Cu5]6+ [VO4]37 y z x Figure 9. The crystal structure of averievite Cu5O2(VO4) .MCl. L14 L15 A B A B Figure 10. The oxocentred layered complexes L14 and L15. Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic compounds 147L20. The [O4M3] double layer is made up of two L12 layers edge-linked to one another. 5. Oxocentred framework complexes The classification of three-dimensional polyhedral structures is one of the important problems in the crystal chemistry of inorganic compounds.Tables 9 and 10 present the types of oxocentred framework complexes based on [OM4] tetrahedra and the chemical compounds containing them. F1 (Fig .11). The oxocentred type F1 framework is a reverse analogue of the cristobalite framework, which has been frequently noted by many investigators (see, for example, Belov 77).The crystal structure of cuprite Cu2O277, 278 consists of two inter- penetrating electrically neutral anticristobalite [OCu2] frame- works (Fig. 11a). When univalent copper is replaced by divalent copper, the [OCu2] framework (Fig. 11b) acquires a 2+ charge per tetrahedron. The introduction of additional anions into this framework in order to compensate for the charge leads to the Table 10.Chemical compounds containing oxocentred framework com- plexes based on [OM4] tetrahedra. Num- Type of Chemical Chemical Ref. ber complex formula compound of complex F 1 {uB, 3 1}[OM2] [OCu2] Cu2O (cuprite) 278 [OCu2] Cu2OCl2 279 (melanothallite) Cu2O(SeO3), P21/n 51 Cu2O(SeO3), P213 51 [OPb2] Pb2O 280 Pb2OF2 281 [OPd2] Pd2OCl2 282 [OFe2] b-Fe2O(PO4) 283, 284 [ONiCr] NiCrO(PO4) 283 [OA2] (A=Hg, A2(B2O6)O (B=Ru, 285, Cd, Ag, Bi, Pb Rh, Ti, Cr etc.) 286, etc.) (pyrochlores) 287 F 2 {uB, 3 1}[OM2] [O2MgAl3] MgAl3O2(SiO4)(BO3) 288 F3 {uB, 3 1}[OM] [OZn] ZnO (zincite) 289, 290 [OBe] BeO (bromellite) 291 F4 {lB, 3 1}[O6M11] [O12Bi4Ag18] Bi4Ag18O12 292 F5 {uB, 3 1}[OM] [OCu] CuO (tenorite) 293 AgO 293 F6 {lB, 3 1}[O2M3] [O2Cd3] Cd3O2Cl2 294 F7 {uB, 3 1}[OM] [O2CuFe] CuFeO2 (delafossite) 295, 296 [O2AgFe] AgFeO2 297 [O2CuM] CuMO2 298 (M=Al, (M=Al, GaSc, Y) GaSc, Y) F7 {uB, 3 1}[OM] CuAlO2 299 [O2CuMn] CuMnO2 300 (crednerite) F8 {uB, 3 1}[O2M3] [O4Cu5Sn] Cu5Sn(BO3)2O4 301 F9 {uB, 3 1}[OM] [(F,O)Pb] Pb12Ta9O20F29 302 F10 {uB, 3 1}[O2M] [O2Ce] CeO2 303 F11 {lB, 3 1}[O3M2] [O3FeMn] FeMnO3 304 [O3CuTi] Cu17xTi17x 305 F12 {lB, 3 1}[OM] [OIn] In6O6(WO6) 306 F13 {lB, 3 1}[O2M3] [O2La3] La3Ir3O11 307 [O2Bi3] Bi3Ru3O11 308, 309 F14 {uB, 3 1}[O2M3] [O2Co2.1Al0.9] Co2.1Al0.9BO5 310 [O2Ni2Al] Ni2AlBO5 310 [O2Cu2Al] Cu2AlBO5 310 F15 {uB, 3 1}[O3M2] [O3Al2] Al2O3 (corundum) 311 F16 {uB, 3 1}[O2M3] [O2Ag2Pb] Ag2PbO2 312, 313 [O2Cu2Pb] PbCu2O2 314 F17 {hB, 3 1}[O3M4] [O3Ag3Bi] Ag3BiO3 315 F18 {uB, 3 1}[O2M3] [O4Ag5Bi] Ag5BiO4 315 F19 {uB, 3 1}[O6M7] [O6Ag5Pb2] Ag5Pb2O6 312 F20 {uB, 3 1}[O9M4] [O18Ag25Bi3] Ag25Bi3O18 316 F21 {lB, 3 1}[O10M13] [O10Pb13] Pb13O10Br6 317 a b Figure 11. The crystal structure of cuprite Cu2O and the [OCu2] double framework made up of [OCu4] tetrahedra (a) and the F1 framework (b).Table 9. Statistics of oxocentred framework complexes based on [OM4] tetrahedra.Num- ML L P B O: T m n p Connectedness ber formula F 1 1 1 2 uB 1 : 2 1 1 1 (4: 1 ± 4) F 2 1 1 2 uB 1 : 2 1 1 1 (4: 1 ± 4) F3 1 1 1 uB 1 : 1 1 1 1 (12: 1 ± 12) F4 1 1 1 lB 6 : 11 2 1 A1 (5: 1 ± 5) B2 (5: 1 ± 5) F5 1, 2 1, 2 2 uB 1 : 1 1 1 1 (10: 1 ± 8; 2 ± 2) F6 1, 2 1, 2 4 lB 2 : 3 1 1 1 (6: 1 ± 5; 2 ± 1) F7 1, 2 1, 2 1 uB 1 : 1 1 1 1 (13: 1 ± 10; 2 ± 3) F8 1, 2 1, 2 2 uB 2 : 3 1 1 1 (7: 1 ± 6; 2 ± 1) F9 1, 2 1, 2 1 uB 1 : 1 3 2 A1 (8: 1 ± 4; 2 ± 4) B1 (8: 1 ± 4; 2 ± 4) C1 (10: 1 ± 8; 2 ± 2) F10 2 1, 2 2 uB 2 : 1 1 1 1 (22: 1 ± 16; 2 ± 6) F11 2 1, 2 2 lB 3 : 2 1 1 1 (16: 1 ± 12; 2 ± 4) F12 2 1, 2 5 lB 1 ; 1 1 1 1 (9: 1 ± 6; 2 ± 3) F13 1, 2 1, 2 4 lB 2 : 3 1 1 1 (4: 1 ± 1; 2 ± 3) F14 1, 2 1, 2 4 uB 2 : 3 2 2 A1 (8: 1 ± 7; 2 ± 1) B1 (6: 1 ± 6) F15 1, 2 1, 2 2 uB 3 : 2 1 1 1 (16: 1 ± 12; 2 ± 4) F16 1, 2 1, 2 2 uB 2 : 3 1 1 1 (7: 1 ± 6; 2 ± 1) F17 1, 2 1, 2 2 hB 3 : 4 3 3 A1 (8: 1 ± 7; 2-1) B1 (10: 1 ± 9; 2 ± 1) C1 (10; 1 ± 10 F18 1, 2 1, 2 2 uB 2 : 3 4 2 A1 (9: 1 ± 8; 2 ± 1) B1 (8: 1 ± 8) C1 (8: 1 ± 8) D1 (8: 1 ± 8) F19 1, 2 1, 2 2 uB 6 : 7 1 1 1 (15: 1 ± 14; 2 ± 1) F20 1, 2 1, 2 2 oB 9 : 14 2 2 A1 (10: 1 ± 8; 2 ± 2) B2 (7: 1 ± 6; 2 ± 1) F21 1, 2 1, 2 3 lB 10 : 13 5 5 A1 (4: 1 ± 2; 2 ± 2) B1 (5: 1-2; 2 ± 3) C1 (6: 1 ± 3; 2 ± 3) D1 (7: 1 ± 3; 2 ± 4) E1 (8: 1 ± 4; 2 ± 4) 148 S V Krivovichev, S K Filatov, T F Semenovacrystal structures of melanothallite Cu2OCl2 279 and Cu2O(SeO3)2 (two modifications 51). Similar frameworks with additional anions occur also in the Pd2OCl2 282 and Pb2OF2 281 structures.The latter structure was examined by Bergerhoff and Paeslack 19 as an oxocentred framework. Pannetier and Lucas 286 suggested that the A2B2O6O0 pyrochlore structural type, in particular, be con- sidered as one containing the cuprite-likeA2O0 (A=Sc, Y, Ln, Bi, Cd, Hg, Pb, etc.) framework. The following considerations were adduced in support of this model: firstly, the model makes it possible to consider the characteristic features of the disposition of the O0 atom (position 8b), the orbitals of which are sp3-hybridised and the coordination is represented by a regular tetrahedron; secondly, the distortion of the cubic pyrochlore structure may be compared with the observed distortions of the polymorphic modifications of silica SiO2; thirdly, if position A is occupied by a d10 atom of type Hg2+, Cd2+, or Ag+, the A±O0 bond becomes stronger than the A±O bond and the O0 oxygen becomes less mobile.The possibility of describing the pyrochlore structure taking into account the tetrahedral coordination of the O0 oxygen has also been pointed out by Belov et al.287 F2. The oxocentred [O2MgAl3] framework, made up of L1 layers linked via corners not participating in the formation of the layer, may be identified in the crystal structure of grandidierite.288 F3.The F3 framework is the oxocentred version of the wurtzite structure. Four [OZn4] tetrahedra converge at each corner of this framework. F4. The oxocentred [O6M11] framework has been found in the Bi4Ag18O12 structure.292 This framework consists of two types of fundamental chains � two-period C5 chain and a four-period chain formed as a result of the corner-linking of tetrahedra.In the structure of this compound, the chains are parallel to the y axis. This structure shows that the topological equivalence of all the tetrahedra in the polyion does not as yet ensure their configura- tional equivalence. In this structure, there are two configurational types of tetrahedra belonging to one topological class.F5. The oxocentred framework of this type is made up of C7 lanarkite chains linked by the corners of the tetrahedra so that four tetrahedra converge at a single corner. F6. The F6 framework is made up of L8 layers linked by non- shared corners of the tetrahedra. F7. The delafossite CuFeO2 structural type consists of a framework made up of continuous hexagonal layers of [OCuFe3] tetrahedra linked via corners at which the copper atoms are located; within the layer, the linking is via the iron atoms.295, 296 F8.The [O2M3] framework may be represented as consisting of single type C12 chains. F9. The type F9 framework is made up of C1 chains linked in the following way: six C1 chains fitted together edgewise form a six-fold chain belonging to the OnMn+2 family.The complex chains linked in this way are linked via the corners of the tetrahedra to form a framework dividing space into a series of broad parallel channels with a square cross-section. In the crystal structure of the compound Pb12Ta9O20F29, infinite columns of [TaO6] octahedra are accommodated in these channels.302 F10, F11, F12.The frameworks of these types may be regarded as derivatives of the fluorite CaF2 structure, which can be represented in its turn as one consisting of [FCa4] tetrahedra. CeO2,303 the structure of which is made up of [OCe4] tetrahedra, is an analogue of fluorite. The structural type of bixbyite 304, 305 corresponds to a defective fluorite framework, like the [OIn] framework in the crystal structure of In6O6(WO6).306 F13 (Fig. 12a). The F13 type framework is made up of finite groups I6 linked by nonshared corners. The La3Ir3O11 struc- ture 307 includes two interpenetrating [O2La3] frameworks. F14 (Fig. 12b). The three-dimensional [O2M3] structure, characteristic of the crystal structures of aluminoborates M2AlBO5 (M=Co, Cu, Ni), has one-dimensional distorted hexagonal cavities in which the (BO3) anions are accommo- dated.310 F15.The type F15 framework describes the crystal structure of corundum Al2O3 when it is considered taking into account the tetrahedral coordination of the oxygen atoms.311 It is possible to describe the structure as hexagonal close packing of the oxygen atoms in which octahedral cavities are filled by aluminium atoms.However, the latter are appreciably displaced from the centres of the octahedral cavities, which is due to the tendency of oxygen to acquire the ideal tetrahedral coordination. The structure of corundum is also remarkable because three [OAl4] tetrahedra are linked together in it via a single [Al ± Al] edge. F16. The [O2M3] framework consists of C12 single chains linked via corners participating in edge-linking within the chain.F17. Analysis of the Ag3BiO4 structure showed that it contains a complex oxocentred framework made up of [OAg3Bi] tetrahedra of three configurational types.315 F18. In the crystal structure of Ag5BiO4, there is a complex framework with the ratio O:M=2 : 3.315 This framework is formed as a result of the intertwining of C5 single chains, so that five-petal `flowers' made up of oxocentred tetrahedra converging at one corner are produced.F19. The C12 chains in the Ag5Pb2O6 structure are joined together in threes to form columns with a trigonal symmetry and are linked into a framework via the corners of the tetrahedra not participating in the linking process.312 F20. In the study of the crystal structure of Ag25Bi3O18 316 within the framework of the approach employed, a single common edge [Bi &psmn; Ag] between three [OAg3Bi] tetrahedra was noted. This framework consists of [OAg3Bi] tetrahedra of two topological types. The type A tetrahedra, linked to form triple edge `knots', consist of vertical columns with symmetry 3.The type B tetrahe- dra form groups made up of six tetrahedra converging at one corner.These groups link the vertical `knotted' columns into a three-dimensional framework. F21. The F21 framework was identified by Riebe and Kel- ler 317 in the crystal structure of Pb13O10Br6. It consists of infinite chains of corner-linked [OPb4] tetrahedra. These complex chains, arranged crosswise in the structure, are linked via the corners of the tetrahedra into a three-dimensional framework. 6. Structures with different oxocentred complexes In conclusion of the description of the topological types of oxocentred complexes, it is essential to note the existence of the structural type with two different complexes based on [OM4] tetrahedra. In the crystal structures of the compounds Pb11Si3O17 155 (Fig. 13), and Pb11Ge3O17,156 there are two oxo- centred polyions of different dimensionality � the C3 chain and the L19 layer.The [OPb2] C3 chains are arranged in the (001) plane in the form of a layer (without mutual linking), while the [O4Pb7] L19 layer is parallel to this plane. These layers alternate, the orthosilicate and diorthosilicate groups [SiO4]47 and [Si2O7]67 being located in the space between them.The crystal- a b A B A B 2 2 2 2 2 Figure 12. The oxocentred frameworks F13 (a) and F14 (b). Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic compounds 149chemical formula of the Pb11Si3O17 structure should be written thus: {IB, 12 1}[O4Pb7]({uB, 11 1}[OPb2])2[SiO4]{f }[Si2O7]. The presence in this structure of different polycations and poly- anions can be accounted for by their mutual stabilisation.The presence of silicate anions of two types and of different oxocentred structural units weakens the stresses generated. V. Statistics of the corner and edge-linking [OM4] tetrahedra The ability of oxocentred tetrahedra to be linked together in two different ways (via corners and edges) has led to the statistical analysis of different types of linking among the 63 polyions described.We shall define the sharing index of an element of the tetrahedral group (corner, edge) as the number of tetrahedra between which the element is shared regardless of the method of sharing. The average sharing index of the corners of the tetrahe- dron n will be defined as the average of the sharing indices of its corners.Thus, if n1, n2, n3, and n4 are the indices of the corners of the tetrahedron, it follows that v=Pvi 4 , i=1 ± 4 . By analogy with n, we shall define the average sharing index of the edges of the tetrahedron e: e= Pei 6 , i=1 ± 6 , where ei is the sharing index of the ith edge in the tetrahedron. The average sharing index of an element [a corner (n) or an edge (e)] in the complex will be defined as the arithmetical mean of the sharing indices of the elements of topologically different tetrahedra.Account is taken of the number of tetrahedra of the given topological type in the complex. Thus, if there are two topological types of tetrahedra, A and B, in the complex in proportions of 2 : 1, then the average sharing index of the corners in the polyion is calculated by the formula v à 2vA á vB 3 , where nA and nB are the average sharing indices of the corners in the tetrahedra A and B.The average sharing indices of the corners and edges in oxocentred complexes are presented in Table 11. For each dimen- sionality, the values have been averaged with respect to the number of polyions. It was found that the values of n naturally increase on passing from finite to framework complexes: 1.604 for I, 2.437 for C, 3.376 for L, and 3.886 for F (Fig. 14) As regards edge-linking, the values of e increase from 1.153 to 1.427 (1.278 for chains) on passing from finite layered complexes, but in the case of frameworks e diminishes to 1.328. This shows that edge-linking is most favourable for the linking of the [OM4] tetrahedra into a layer, i.e.into a two-dimensional structure. For framework complexes, this type of linking is less common apparently because the involvement of a large number of edges in a tetrahedral structure leads to an unduly high concentration of oxygen atoms and a decrease in the stability of the complex. The frameworks are formed preferentially by the corner-linking of the tetrahedra.The average sharing indices of the corners and edges for oxocentred complexes as a whole, calculated from the data [SiO4]47 [OPb2]2+ [O4Pb7]6+ [Si2O7]67 z x y Figure 13. The crystal structure of Pb11Si3O17. Table 11. The average connectedness indices of the corner (n) and the edge (e) in oxocentred complexes. Num- v e Num- v e Num- v e ber ber ber I 1 1 1 L1 1.750 1 F 1 2 1 I 2 1.25 1 L2 1.750 1 F 2 2 1 I 3 1.375 1 L3 4 1.500 F 3 4 1 I4 1.50 1.167 L4 6 1.750 F4 2.250 1 I5 2 1.250 L5 3.500 1.500 F5 4 1.333 I6 2.500 1.500 L6 3.667 1.556 F6 2.750 1.167 1.604 a 1.153 a L7 3.750 1.583 F7 5 1.500 C1 1.500 1 L8 2.500 1.167 F8 3 1.167 C2 1.750 1 L9 2.750 1.333 F9 4 1.556 C3 2.500 1.333 L10 2 1.167 F10 8 2 C4 3 1.444 L11 2.750 1.167 F11 6 1.667 C5 1.500 1 L12 4 1.667 F12 4 1.500 C6 2.000 1.083 L13 4 1.667 F13 2.750 1.500 C7 2.000 1.333 L14 3.250 1.500 F14 2.875 1.083 C8 3 1.500 L15 2.667 1.389 F15 6 1.667 C9 3.333 1.556 L16 2.875 1.444 F16 3 1.167 C10 4.333 1.611 L17 3.571 1.619 F17 3.500 1.111 C11 4.333 1.611 L18 4.091 1.424 F18 3.125 1.042 C12 1.750 1.167 L19 2.450 1.267 F19 5 1.167 C13 2.250 1.250 L20 6 1.833 F20 5 1.222 C14 1.750 1.167 3.376 a 1.427 a F21 3.350 1.533 C15 1.667 1.111 3.886 a 1.328 a C16 2.33 1.278 2.437 a 1.278 a a Average value.v, e 4.0 3.0 2.0 1.0 0 1 2 D �1 �2 Figure 14. Dependence of the average sharing indices of the corners (1) and edges (2) on the dimensionality of the oxocentred complexes. 150 S V Krivovichev, S K Filatov, T F Semenovapresented in Table 11, proved to be 3.139 and 1.330 respectively.Thus each corner in the oxocentred complexes based on the [OM4] tetrahedra belongs on average to three tetrahedra and each edge belongs to 11 3 tetrahedra. We may note that the edge-linking of tetrahedra inevitably increases the sharing index of their corners. Thus one (out of six) shared edge of the tetrahedra increases the average sharing index e by 1/6 and, by creating two (out of four) common corners, it increases n by 0.5.If the fraction due to edge-linking is subtracted from n, we obtain the following values of n for pure corner-linking: 1.145 for I, 1.603 for C, 2.098 for L, and 2.902 for F. This demonstrates yet again the importance of corner-linking in the organisation of oxocentred frameworks.VI. Rules governing the linking of oxocentred [OM4] tetrahedra The description of the established types of cationic complexes based on oxocentred [OM4] tetrahedra can be usefully completed by the rules according to which individual tetrahedra are linked together into a structural fragment. 1. The [OM4] tetrahedra can be linked together via corners (M) and/or edges (MM). 2. One corner may be shared by more than two oxocentred tetrahedra but as a rule by not more than eight tetrahedra. 3. One edge is usually shared by not more than two oxocentred tetrahedra and in exceptional cases by three tetrahedra. 4. The corner-linking of the [OM4] tetrahedra is characteristic of polyions of any dimensionality, while edge-linking is primarily characteristic of finite chain and layered structural units.The frameworks are formed mainly as a result of the corner-linking of tetrahedra. The elucidation of the maximum number of tetrahedra con- verging at one corner constitutes an interesting problem. If the set of tetrahedra (`petals') converging at one corner is called a `flower', then the maximum number of `petals' (8) has been noted in topologically identical `flowers' produced from the four-fold layer L4, the double layer L20, and the fluorite-like framework F10.The central atoms in these `petals' are Bi, Ba, and Ce respectively. It was foun, among the oxocentred com- plexes known to us, there are eleven topologically different `flowers' in which the number of `petals' ranges from 5 upwards. Evidently the `flower' with eight `petals' constitutes the limit, the addition of yet another tetrahedron to the latter being impossible without the formation of a face-linkage.The instance where three tetrahedra are edge-linked has not apparently been encountered in the crystal structures of anionic complexes with tetrahedral structural units, but does occur in the oxocentred corundum frameworks [O3Al2] and [O18Ag25Bi3].In the latter case, the steric interactions of theMcorners not involved in the three-fold edge-linking of two neighbouring tetrahedra are weakened as a result of the inclination of the M±M edge relative to the horizontal. If one edge in the tetrahedral complexes may be shared by not more than three tetrahedra, then the distance R between nonshared M corners of neighbouring tetrahedra corre- sponds exactly to the length of theM±Medge.If four tetrahedra are linked via a single edge, (without a face-linkage), the distanceR cannot be greater than or equal to the length of the M±M edge without complete loss of tetrahedral geometry by the linked complexes. Sn2O(SO4), Pb2O(SO4) (lanarkite), and Cu2O(SO4) (dolero- phanite) may serve as examples of compounds in which the chemical composition of the cations influences the topology of the oxocentred polyion.In the first compound, there are finite groups I6 having the composition [O4Sn8], in lanarkite there are C7 [OPb2] chains, whilst in dolerophanite there are L10 [OCu2] layers. Analysis of the incidence of various structural units based on [OM4] tetrahedra shows that complexes made up of configura- tionally and topologically equivalent tetrahedra are commonest.This is fully consistent with Pauling's rule. VII. Statistics of theM±O bond lengths and M±O±Mbond angles in [OM4] complexes It was stated above that, as a consequence of the edge-linking of two tetrahedra, the value of the opposite bond angle diminishes. The average values of the M±O±M bond angles based on the M±Medge shared by two [OM4] tetrahedra are listed in Table 12 for M=Cu, Sn, Pb, and La.{ Evidently the M±O±M angle depends on the size of the atom M.The greater the M±O bond length, the smaller the diminution of the M±O±M angle. It is of interest that the average value<M±O±M>for all the atomsM considered is close to the `ideal' value of 109.58.The decrease in one or several M±O±M angles, induced by the presence of a common edge in the tetrahedron, is compensated by the increase in the bond angles based on the nonshared edges. Another fundamental feature of [OM4] complexes is the possibility of the linking at one atom M of several [OM4] tetrahedra. Table 13 presents the averageM±O bond lengths for M corners of different connectedness in complexes with M=Cu or Pb.TheM±Obond lengths for a nonsharedMcorner and for a M corner linking two [OM4] tetrahedra do not actually differ. When the M±M edge is shared and the number of tetrahedra converging at an atom M increases, the M±O bond length also increases. When a corner is shared by three tetrahedra so that one tetrahedron is edge-linked to a second tetrahedron and corner- linked to a third tetrahedron (Table 13), the M±O bond length forM=Pb increases sharply (2.35 A).When four [OPb4] tetrahe- dra are linked via a single edge so that a tetrahedron is edge-linked to two others and corner-linked to the fourth, the bond length also increases (2.40 A). We may note that in the last case we did not take into account in the calculation of the M±O bond length the type L12 layered [OPb] complexes in which all the corners of the [OPb4] tetrahedron are shared in this way.For these complexes, theM±O bond length is on average 2.34 A (24 bonds were taken into account) (the limits of their variation were 2.31 ± 2.36 A), i.e. smaller by 0.06 A than for the analogous corners in the remaining complexes.Overall, one may say that an increase in the number of [OM4] tetrahedra converging at oneMcorner induces an increase in theM±O bond length. { Only data for [OM4] complexes with a single cationMwere used for the analysis. Table 12. The average M±O±Mbond angles in [OM4] complexes. Bond M±O /A M±O±M /deg a M±O±M /deg b I II I II Cu7O 1.94 93.5 12 109.6 72 (91.4 ± 95.9) Sn7O 2.26 101.8 3 109.0 6 (98.1 ± 104.4) Pb7O 2.33 103.1 83 109.5 120 (94.4, 98.2 ± 109.2) La7O 2.36 104.4 32 109.4 48 (101.6 ± 107.6) average value 109.5 246 Note.The following designations have been adopted: I � average values of the angles, the limits of the variation of the angle in the structure being indicated in brackets; II�number of values taken into account. a Values for the angle based on the common edge.b Values for all the angles in the tetrahedron. Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic compounds 151VIII. Conclusion The topological types of the structural units based on oxocentred [OM4] tetrahedra have been described in the present review. In all, 63 different [OM4] polyions have been identified; 6 finite, 16 chain, 20 layered, and 21 framework polyions. Since the aim of the present review was the discovery and systematic topological treatment of the oxocentred complexes, we have hardly touched upon the analysis of the geometrical and energetic characteristics of specific crystal structures and on their relation with the type of organisation of the [OM4] tetrahedra to form a complex.Only the relation between the physical properties of the compounds con- taining [OM4] groups and the characteristic features of the linking of these tetrahedra into a complex has been illustrated (for georgbokiite). The studies initiated will be continued by a detailed analysis of the lengths and angles in various types of oxocentred complexes, the study of the correlation of the structures of the compounds described from the standpoint of the crystal chemistry of oxocentred complexes with the properties of these compounds, the discovery of a relation between the traditional and proposed methods for the description of structures, and questions concern- ing the existence of oxocentred complexes in noncrystalline media, for example in gases. In writing the review, the authors widely employed the structural data bank Inorganic Crystal Structure Database (ICSD) supplied free of charge to the Department of Crystallog- raphy of the St.Petersburg University by Prof.H Bradaczek of the Free University of Berlin.The authors are grateful to Prof. P M Zorkii for valuable advice in connection with the discussion of the review.The review has been written with the financial support of the Russian Foundation for Basic Research (Project No. 96-05-65576) and also of the `Central Europe' section of the Russian Academy of Natural Sciences. References 1. B Holmberg Acta Chem. Scand., Ser. A 30 680 (1976) 2. B Holmberg Acta Chem. Scand., Ser. A 30 797 (1976) 3. L Bengtsson, B Holmberg, A Iverfeldt,M Maeda, H Othaki Inorg. Chim.Acta 146 233 (1988) 4. L Bengtsson, B Holmberg J. Chem. Soc., Faraday Trans. 1 85 305 (1989) 5. L Bengtsson, B Holmberg J. Chem. Soc., Faraday Trans. 1 85 317 (1989) 6. L Bengtsson, F Frostemark, S Ulvelund J. Chem. Soc., Faraday Trans. 87 1141 (1991) 7. F Frostemark, L Bengtsson, B Holmberg J. Chem. Soc., Faraday Trans. 90 2401 (1994) 8. A I Boldyrev, P von R Schleyer J.Am. Chem. Soc. 113 9045 (1991) 9. D M Cox, D J Trevor, R L Whetten, E A Rohlfing, A Kaldor J. Chem. Phys. 84 4651 (1986) 10. A I Boldyrev, I L Shamovsky, P von R Schleyer J. Am. Chem. Soc. 114 6469 (1992) 11. A I Boldyrev, J Simons, P von R Schleyer Chem. Phys. Lett. 233 266 (1995) 12. P J Ziemann,A W Castleman Jr Phys. Rev. B, Condens. Matter 46 13 480 (1992) 13.H T Deng, Y Okada,M Foltin, A W Castleman Jr J. Phys. Chem. 98 9350 (1994) 14. C H Wu, H , H R Ihle J. Chem. Phys. 70 1815 (1979) 15. C H Wu Chem. Phys. Lett. 139 157 (1987) 16. PDDao,KI Petersen,AWCastleman Jr J. Chem. Phys. 80 563 (1984) 17. E-U Wurthwein, P von R Schleyer, J A Pople J. Am. Chem. Soc. 106 6973 (1984) 18. G B Kauffman, M Karbassi, G Bergerhoff J. Chem.Educ. 61 729 (1984) 19. G Bergerhoff, J Paeslack Z. Kristallogr. 126 112 (1968) 20. D Carre,M Guittard, S Jaulmes, A Mazurier,M Palazzi, M P Pardo, P Laurelle, J Flahaut J. Solid State Chem. 55 287 (1984) 21. L Bengtsson, B Holmberg J. Chem. Soc., Faraday Trans. 86 351 (1990) 22. K Sahl Z. Kristallogr. 132 99 (1970) 23. E Fluegel-Kahler Acta Crystallogr. 16 1009 (1963) 24. H Effenberger Monatsh.Chem. 116 927 (1985) 25. K V Damodaran, K J Rao Chem. Phys. Lett. 148 57 (1988) 26. B G Rao, K J Rao, J Wong J. Chem. Soc., Faraday Trans. 1 84 1173 (1988) 27. B G Rao, K J Rao, J Wong J. Chem. Soc., Faraday Trans. 1 84 1179 (1988) 28. G Davies, M A El-Sayed, A El-Toucky, M Henary Inorg. Chem. 25 4479 (1986) 29. C F George Jr Inorg. Chem. 27 635 (1988) 30. R E Norman,N J Rose,R E Stenkamp Acta Crystallogr., Sect.C 45 1707 (1989) 31. F S Keij, J G Haasnoot, A J Oosterling, J Reedijk, C J O'Connor, J H Zang, A L Spek Inorg. Chim. Acta 181 185 (1991) 32. S Teipel, K Griesar, W Haase, B Krebs Inorg. Chem. 33 456 (1994) 33. L Chen, S R Breese, R J Rousseau, S Wang, L K Thompson Inorg. Chem. 34 454 (1995) 34. J Reim, K Griesar, W Haase, B Krebs J.Chem. Soc., Dalton Trans. 2649 (1995) 35. R C Dickinson, F T Helm,W A Baker Jr, T D Black, W H Watson Jr Inorg. Chem. 16 1530 (1977) 36. L Hiltunen,M LeskelaÈ ,M MaÈ kela È , L NiistoÈ Acta Chem. Scand., Ser. A 41 548 (1987); 37. Yu A Simonov,M A Yampol'skaya, M I Belinskii, A A Dvorkin, in Strukturnye Issledovaniya Neorganicheskikh i Organicheskikh Soe- dinenii (Structural Investigation of Inorganic and Organic Compounds) (Shtiintsa: Kishinev, 1985) p. 40 38. S K Filatov, T F Semenova, L P Vergasova Dokl. Akad. Nauk 322 536 (1992) a 39. S K Filatov, T F Semenova, L P Vergasova Progr. Universitety Rossii. Geologiya 2 16 (1994) Table 13. TheM±O bond lengths forMcorners with different connected- ness in [OM4] tetrahedra. Corner Number Number Number (M ± O)av Limits of of tetra- of tetra- of com- of bonds /A variation hedron a hedra con- pounds taken into ofM±O verging at taken into account /A oneM account corner Cu7O 1 15 43 1.92 1.90 ± 1.95 2 13 38 1.92 1.86 ± 2.00 2 10 36 1.94 1.81 ± 2.00 4 2 8 1.96 1.91 ± 2.02 Pb7O 1 5 11 2.26 2.18 ± 2.32 2 5 7 2.25 2.20 ± 2.34 2 11 38 2.27 2.23 ± 2.32 3 5 15 2.27 2.19 ± 2.34 3 3 19 2.35 2.34 ± 2.37 4 8 33 2.40 2.39 ± 2.41 a The filled circle designates the corner where two tetrahedra are linked and the numeral 2 at the filled circle indicates that a further two tetrahedra are attached to the given tetrahedron via a corner; the semibold edge signifies that yet another tetrahedron has been attached to the given tetrahedron via an edge. 2 152 S V Krivovichev, S K Filatov, T F Semenova40. S K Filatov, S V Krivovichev, T F Semenova, in XIII Mezhdunar.Soveshch. po Rentgenograéi Mineral'nogo Syr'ya (Tez. Dokl.) Belgorod, 1995 [The XIIIth International Meeting on X-Ray Diffractometry of Mineral Raw Materials (Abstracts of Reports) Belgorod, 1995] p. 35 41. S V Krivovichev, S K Filatov, T F Semenova, in VII Soveshch. po Kristallokhimii Neorganicheskikh i Koordinatsionnykh Soedinenii (Tez.Dokl.), Sankt-Peterburg, 1995 [The VIIth Meeting on Crystal Chemistry of Inorganic and Coordination Compounds (Abstracts of Reports), St.-Petersburg, 1995] p. 52 42. J Galy, J J Bonnet, S Andersson Acta Chem. Scand., Ser. A 33 383 (1979) 43. L P Vergasova, S K Filatov, E K Serafimova, T V Varaksina Zap. Vsesoyuzn. Miner. O-va 459 (1988) 44. T V Varaksina, V S Fundamensky, S K Filatov, L P Vergasova Mineral.Mag. 54 613 (1990) 45. F Scordari, F Stasi Neues Jhrb. Mineral. Abh. 241 (1990) 46. G L Starova, S K Filatov, V S Fundamensky, L P Vergasova Mineral. Mag. 55 613 (1991) 47. L P Vergasova, S K Filatov, E K Serafimova, G L Starova Dokl. Akad. Nauk SSSR 299 961 (1988) a 48. K M S Etheredge, S-J Hwu Inorg. Chem. 35 5278 (1995) 49.M Brunel-Laugt, A Durif, J Guitel J. Solid State Chem. 25 39 (1978) 50. J B Anderson, G L Shoemaker, E Kostiner J. Solid State Chem. 25 49 (1978) 51. H Effenberger, F Pertlik Monatsh. Chem. 117 887 (1986) 52. MBrunel-Laught, J C Guitel Acta Crystallogr., Sect. B 33 3465 (1977) 53. M Staack, Hk Muller-Buschbaum Z. Naturforsch., B Chem. Sci. 51 1279 (1996) 54. R D Shannon, C Calvo Acta Crystallogr., Sect. B 29 1338 (1973) 55.R W Birnie, J M Hughes Am. Mineral. 64 941 (1979) 56. G Lundgren, G Wernfors, T Yamaguchi Acta Crystallogr., Sect. B 38 2357 (1982) 57. K Sahl Z. Kristallogr. 156 209 (1981) 58. A Latrach, B F Mentzen, J Bouix Mater. Res. Bull. 20 853 (1985) 59. B F Mentzen, A Latrach, J Bouix, P Boher, P Garnier Mater. Res. Bull. 19 925 (1984) 60. A Latrach, B F Mentzen, J Bouix Mater. Res.Bull. 20 1081 (1985) 61. K Kato Acta Crystallogr., Sect. B 35 795 (1979) 62. M Cooper, F C Hawthorn Am. Mineral. 79 550 (1994) 63. R C Rouse, P J Dunn Neues Jhrb. Mineral. Abh. 519 (1986) 64. S Morita, K Toda J. Appl. Phys. 55 2733 (1984) 65. J C Ruckman, R T W Morrison, R H Buck J. Chem. Soc., Dalton Trans., Inorg. Chem. 426 (1972) 66. B F Mentzen, A Latrach, J Bouix, A W Hewat Mater.Res. Bull. 19 549 (1984) 67. F Pertlik Mineral. Petrol. 36 85 (1987) 68. A R Rae-Smith, A K Cheetham, H Fuess Z. Anorg. Allg. Chem. 510 46 (1984) 69. K Waltersson Acta Crystallogr., Sect. B 32 1485 (1976) 70. H-J Meyer, G Meyer, M Simon Z. Anorg. Allg. Chem. 596 89 (1991) 71. G Baud, J P Besse, R Chevalier,M Gasperin J. Solid State Chem. 29 267 (1979) 72. P Gall, P Gougeon Acta Crystallogr., Sect. C 48 1915 (1992) 73. S V Krivovichev, T F Semenova, S K Filatov, in Abstracts of Reports at the International Conference `Powder Diffraction and Crystal Chemistry' St Petersburg, Russia, 1994 p. 91 74. S K Filatov Vysokotemperaturnaya Kristallokhimiya (High- Temperature Crystal Chemistry) (Leningrad: Nedra, 1990) 75. D Yu Pushcharovskii Struktura i Svoistva Kristallov (The Structure and Properties of Crystals) (Moscow: Izd.Mosk. Gos. Univ., 1985) 76. F Liebau Structural Chemistry of Silicates. Structure, Bonding and Classiécation (Berlin: Springer, 1985) 77. N V Belov Ocherki po Strukturnoi Mineralogii (Essays on Structural Mineralogy) (Moscow: Nedra, 1976) 78. P A Sandomirskii, N V Belov Kristallokhimiya Smeshannykh Anion- nykh Radikalov (Crystal Chemistry of Mixed Anionic Radicals) (Moscow: Nauka, 1984) 79.E Parte  Elements of Inorganic Structural Chemistry (Petit-Lancy, 1990) 80. E Parthe , L Gelato, B Chabot,M Penzo, K Cenzual, R Gladyshevskii, in Typix: Standardised Data and Crystal Chemical Characterisation of Inorganic Structure Types Vol. 1 (Heidelberg: Springer, 1993) 81.S V Krivovichev, S K Filatov, T F Semenova Z. Kristallogr. 212 411 (1997) 82. J Lima-de-Faria, E Hellner, F Liebau, E Makovicky, E Parthe Acta Crystallogr., Sect. A 46 1 (1990) 83. R Hoppe, J KoÈ hler Z. Kristallogr. 183 77 (1988) 84. A F Wells Models in Structural Inorganic Chemistry (Oxford: Oxford University Press, 1970) 85. A F Wells Acta Crystallogr., Sect. B 39 39 (1983) 86.A F Wells Philos. Trans. R. Soc. London, A 319 291 (1986) 87. J J de Boer, D Bright, J N Helle Acta Crystallogr., Sect. B 28 3436 (1972) 88. T F Semenova, I V Rozhdestvenskaya, S K Filatov, L P Vergasova Dokl. Akad. Nauk SSSR 304 427 (1989) a 89. L P Vergasova, S K Filatov, E K Serafimova, T F Semenova Dokl. Akad. Nauk SSSR 300 1197 (1988) a 90. D Frerichs, Hk MuÈ ller-Buschbaum Z.Naturforsch., B Chem. Sci. 51 25 (1996) 91. R D Adams, R Layland, C Payen Inorg. Chem. 34 5397 (1995) 92. F-D Martin, Hk MuÈ ller-Buschbaum Z. Naturforsch., B Chem. Sci. 49 1137 (1994) 93. L W Finger Am. Mineral. 70 197 (1985) 94. P Smith, S Garcia-Blanco, L Rivoir Z. Kristallogr. 115 460 (1961) 95. H Behm Acta Crystallogr., Sect. C 39 1317 (1983) 96. E P Moore, H Y Chen, L H Brixner, C M Foris Mater.Res. Bull. 17 653 (1982) 97. M F Debreuille-Gresse,M Drache, F Abraham J. Solid State Chem. 62 351 (1986) 98. T Schleid, G Meyer J. Less-Comm. Met. 127 161 (1987) 99. T Schleid, G Meyer Z. Anorg. Allg. Chem. 553 231 (1987) 100. T Schleid, G Meyer Z. Anorg. Allg. Chem. 554 118 (1987) 101. N L Morrow, L Katz Acta Crystallogr. 24 1466 (1968) 102. B Dickens,W Brown, G Kruger, J Stewart Acta Crystallogr., Sect.B 29 2046 (1973) 103. K Kato, E Takayama, N Kimizuka Acta Crystallogr., Sect. C 39 151 (1983) 104. T Schleid Eur. J. Solid State Inorg. Chem. 28 737 (1991) 105. T Schleid, F Lissner Z. Naturforsch., B Chem. Sci. 49 340 (1994) 106. C L Teske Z. Anorg. Allg. Chem. 531 52 (1985) 107. K B Ploetz, Hk MuÈ ller-Buschbaum Z. Anorg.Allg. Chem. 480 149 (1981) 108. K B Ploetz, Hk MuÈ ller-Buschbaum Z. Naturforsch., B Chem. Sci. 37 108 (1982) 109. K B Ploetz, Hk MuÈ ller-Buschbaum Z. Anorg. Allg. Chem. 484 153 (1982) 110. H Effenberger Tschermaks Mineral. Petrogr. Mitt. 34 279 (1985) 111. A Yamashita, A Kawahara, N Sasaki Acta Crystallogr., Sect. C 51 1483 (1995) 112. F Mazzi, G Rossi Z. Kristallogr. 121 243 (1965) 113.F Mazzi, G Rossi Am. Mineral. 65 123 (1980) 114. T F Semenova, I V Rozhdestvenskaya, I I Bannova, S K Filatov, in V Vses. Soveshch. po Kristallokhimii Neorganicheskikh i Koordi- natsionnykh Soedinenii (Tez. Dokl.), Vladivostok, 1989 [The Vth All-Union Meeting on the Crystal Chemistry of Inorganic and Coordination Compounds (Abstracts of Reports), Vladivostok, 1989] p. 81 115. M Waburg, Hk MuÈ ller-Buschbaum Monatsh. Chem. 117 131 (1986) 116. O Savborg,M Lundberg J. Solid State Chem. 57 135 (1985) 117. K Kato, E Takayama, N Kimizuka Acta Crystallogr., Sect. C 39 148 (1983) 118. J Boje, Hk MuÈ ller-Buschbaum Z. Anorg. Allg. Chem. 618 39 (1992) 119. H L Keller Z. Anorg. Allg. Chem. 491 191 (1982) 120. H L Keller Angew. Chem. 95 318 (1983) 121. H J Riebe, H L Keller Z.Anorg. Allg. Chem. 574 191 (1989) 122. H G von Schnering, R Nesper, H Pelshenke Z. Naturforsch., B Chem. Sci. 36 1551 (1981) 123. R Edwards, R D Gillard, P A Williams Mineral. Mag., 56 221 (1992) 124. S H Hong, A Olin Acta Chem. Scand., Ser. A 28 233 (1974) 125. S H Hong, A Olin Acta Chem. Scand., Ser. A 27 2309 (1973) 126. R C Rouse, D R Peacor Am. Mineral. 79 175 (1994) 127.D R Peacor, P J Dunn,W B Simons, F J Wicks, M Rausdepp Can. Mineral. 26 309 (1988) 128. J S Ogden,M J Ricks J. Chem. Phys. 56 1058 (1972) 129. R K Khanna, Y J Park Spectrochim. Acta, Part A 42 603 (1986) Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic compounds 153130. C F Baes, R E Mesmer, in The Hydrolysis of Cations (New York: Wiley, 1978) p. 420 131. G Johansson, A Olin Acta Chem. Scand. 22 3197 (1968) 132. C Ronay, K Seff Zeolites 13 97 (1993) 133. O Sivborg J. Solid State Chem. 57 148 (1985) 134. R F Klevtsova, L P Kozeeva, P V Klevtsov Izv. Akad. Nauk SSSR, Neorg. Mater. 3 1430 (1967) b 135. E T Lance-Gomez, J M Haschke J. Solid State Chem. 35 357 (1980) 136. S Busche, K Bluhm Z.Naturforsch., B Chem. Sci. 50 1854 (1995) 137. S MuÈ nchau, K Bluhm Z. Naturforsch., B Chem. Sci. 50 1151 (1995) 138. J Schaefer, K Bluhm Z. Anorg. Allg. Chem. 620 1051 (1994) 139. R Norrestam, S Dahl, J O Bovin Z. Kristallogr. 187 201 (1989) 140. R Norrestam, M Kritikos, K Nielsen, I Sotofte, N Thorup J. Solid State Chem. 111 217 (1994) 141. Y Takeuchi, T Kogure Z. Kristallogr. 200 161 (1992) 142.Y Takeuchi, T Watanabe, T Ito Acta Crystallogr. 3 98 (1950) 143. V I Mokeeva Geokhimiya 975 (1968) c 144. Y Takeuchi Geol. Soc. Am. Bull. 66 1624 (1955) 145. M Federico Period. Mineral. 26 191 (1957) 146. R Norrestam, J-O Bovin Z. Kristallogr. 181 135 (1987) 147. Y Takeuchi, N Haga, T Kato, Y Miura Can. Mineral. 16 475 (1978) 148. J A Konnert, D E Appleman, J R Clark, L W Finger, T Kato, Y Miura Am.Mineral. 61 116 (1976) 149. N A Yamnova,M A Simonov, N V Belov Dokl. Akad. Nauk SSSR 238 1094 (1978) a 150. K Bluhm, Hk MuÈ ller-Buschbaum Z. Anorg. Allg. Chem. 582 15 (1990) 151. D A Perkins, J P Attfield J. Chem. Soc., Chem. Commun. 229 (1991) 152. P C Burns,M A Cooper, F C Hawthorne Can. Mineral. 32 397 (1994) 153. S Busche, K Bluhm Z. Naturforsch., B Chem.Sci. 50 1450 (1995) 154. S Jaulmes, A Mazurier,M Guittard Acta Crystallogr., Sect. C 39 1594 (1983) 155. K Kato Acta Crystallogr., Sect. B 38 57 (1982) 156. K Kato, K Hirota, Y Kanke, A Sato, K Ohsumi, T Takase, M Uchida, O Jarchow, K Friese, G Adiwidjaja Z. Kristallogr. 210 188 (1995) 157. J Dugue, T Vovan, J Villers Acta Crystallogr., Sect. B 36 1291 (1980) 158.M J Buerger, V Venkatakrishnan Mater. Res. Bull. 7 1201 (1972) 159. L A Harris, H L Yakel Acta Crystallogr. 22 354 (1967) 160. J P Attfield, J F Clarke, D A Perkins Physica, B (Amsterdam) 180 581 (1992) 161. N A Yamnova, D Yu Pushcharovskii, S V Malinko Kristallograéya 33 349 (1988) d 162. A A Brovkin, E V Pol'shin, V S Brovkina, Yu M Novoselov Kristallograéya 23 107 (1978) d 163. B Moore, T Araki Am.Mineral. 59 985 (1974) 164. R Norrestam, M Kritikos, A SjoÈ din J. Solid State Chem. 114 311 (1995) 165. A Utzolino, K Bluhm Z. Naturforsch., B Chem. Sci. 50 1146 (1995) 166. A Utzolino, K Bluhm Z. Naturforsch., B Chem. Sci. 50 1653 (1995) 167. R K Rastsvetaeva, V I Simonov, N V Belov Dokl. Akad. Nauk SSSR 197 81 (1971) a 168. R K Rastsvetaeva,M I Sirota, N V Belov Kristallograéya 20 259 (1975) d 169.R K Rastsvetaeva Kristallograéya 31 1070 (1986) d 170. R K Rastsvetaeva Zap. Vsesoyuzn. Miner. O-va 696 (1988) 171. R K Rastsvetaeva, V I Andrianov Kristallograéya 31 82 (1986) d 172. A D Khalilov Mineral. Zh. 11 19 (1989) 173. Yu-T Li,V I Simonov,N V Belov Dokl. Akad. Nauk SSSR 167 566 (1966) a 174. M Mellini Tschermaks Mineral. Petrogr.Mitt. 30 249 (1982) 175. R P Shibaeva, N V Belov Dokl. Akad. Nauk SSSR 146 897 (1962)Sa 176. R F Smirnova, I M Rumanova, N V Belov Zap. Vsesoyuzn. Miner. O-va 159 (1955) 177. S Saburi, A Kawahara, C Henmi, T Kusachi, K Kihara Mineral. J. (Jpn) 8 286 (1977) 178. V I Simonov,N V Belov Dokl. Akad. Nauk SSSR 130 1333 (1960) a 179. M Mellini Tschermaks Mineral. Petrogr. Mitt. 28 99 (1981) 180.L Gastaldi, D Carre,M P Pardo Acta Crystallogr., Sect. B 38 2365 (1982) 181. M Leblanc, G Ferey Acta Crystallogr., Sect. C 46 15 (1990) 182. S V Krivovichev, T F Semenova, I V Bannova, I V Rozhdestvenskaya, S K Filatov, in VII Soveshch. po Kristallokhimii Neorganicheskikh i Koordinatsionnykh Soedinenii (Tez. Dokl.), Sankt-Peterburg, 1995 [The VIIth Meeting on the Crystal Chemistry of Inorganic and Coordination Compounds (Abstracts of Reports), St.-Petersburg, 1995] p. 27 183. L Kihlborg, R Norrestam, B Olivecrona Acta Crystallogr., Sect. B 27 2066 (1971) 184. L Kihlborg, R Norrestam Acta Crystallogr., Sect. B 28 3097 (1972) 185. L Bald, R Gruen Naturwissenschaften 68 39 (1981) 186. V P Balko, V V Bakakin Zh. Strukt. Khim. 16 837 (1975) e 187. B Aurivillius Chem.Scr. 11 208 (1977) 188. F Bosselet, B F Mentzen, J Bouix Mater. Res. Bull. 20 1329 (1985) 189. L P Vergasova, S K Filatov, M G Gorskaya, V V Anan'ev, A S Sharov Zap. Vsesoyuzn. Miner. O-va 70 (1989) 190. M G Gorskaya, S K Filatov, I V Rozhdestvenskaya, L P Vergasova Mineral. Mag. 52 411 (1992) 191. M G Gorskaya, L P Vergasova, S K Filatov, D V Rolich, V V Ananiev Zap.Vsesoyuzn. Miner. O-va 95 (1995) 192. L P Vergasova, S K Filatov, E K Serafimova, G L Starova Dokl. Akad. Nauk SSSR 275 714 (1984) a 193. H Effenberger, J Zemann Mineral. Mag. 48 541 (1984) 194. G L Starova, S V Krivovichev, I I Bannova, L P Vergasova, S K Filatov, A Vellish, in VII Soveshch. po Kristallokhimii Neorganicheskikh i Koordinatsionnykh Soedinenii (Tez. Dokl.), Sankt-Peterburg, 1995 [The VIIth Meeting on the Crystal Chemistry of Inorganic and Coordination Compounds (Abstracts of Reports), St.-Petersburg, 1995] p. 39 195. W Krause, H Effenberger, F Brandstatter Eur. J. Mineral. 7 1313 (1995) 196. K Mereiter Fortschr. Mineral. 59 126 (1981) 197. K Mereiter Tschermaks Miner. Petrogr. Mitt. 30 129 (1982) 198. H H Otto Z. Kristallogr. 149 197 (1979) 199. J Boje, Hk MuÈ ller-Buschbaum Z.Anorg. Allg. Chem. 619 521 (1993) 200. K-A Wilhelmi, E Lagervall, O Muller Acta Chem. Scand. 24 3406 (1970) 201. H Mattfeld, G Meyer Z. Anorg. Allg. Chem. 620 85 (1994) 202. O Gabrielson Ark. Mineral. Geol. 2 299 (1958) 203. H Vincent, G Perrault Bull. Soc. FrancË . Miner. Cristallogr. 94 323 (1971) 204. V Kramer, E Post Mater. Res. Bull. 20 407 (1985) 205.J J Finney, E J Graeber, A Rosenzweig, R D Hamilton Mineral. Mag. 41 357 (1977) 206. J Huang, Q Gu, A W Sleight J. Solid State Chem. 105 599 (1993) 207. G Baud, J P Besse, R Chevalier, M Gasperin J. Solid State Chem. 38 186 (1981) 208. J P Besse,M Bolte,G Baud, R Chevalier Acta Crystallogr., Sect. B 32 3045 (1976) 209. N G Shumyatskaya, A A Voronkov, V V Ilyukhin, N V Belov Kristallograéya 21 705 (1969) d 210.N G Shumyatskaya, V V Ilyukhin, A A Voronkov, N V Belov Dokl. Akad. Nauk SSSR 185 1289 (1969) a 211. M Palazzi, S Jaulmes Acta Crystallogr., Sect. B 37 1340 (1981) 212. B Aurivillius Acta Chem. Scand., Ser. A 41 415 (1987) 213. A Watanabe, S Horiuchi, H Kodama J. Solid State Chem. 67 333 (1987) 214. M C Cadee,G C Verschoor,D J W Ijdo Acta Crystallogr., Sect.C 39 921 (1983) 215. H Vinek,H Vollenkle,H Nowotny Monatsh. Chem. 101 275 (1970) 216. M C Cadee,D J W Ijdo,G Blasse J. Solid State Chem. 41 39 (1982) 217. A Teichert, Hk MuÈ ller-Buschbaum J. Alloys. Compd. 182 19 (1992) 218. C W Burnham Z. Kristallogr. 118 337 (1963) 219. P H Ribbe Rev. Mineral. 5 189 (1982) 220. V Agafonov, A Kahn, D Michel,M Perez, Y Jorba J. Solid State Chem. 62 397 (1986) 221. J Barbier Z. Kristallogr. 210 19 (1995) 222. E Bonaccorsi, S Merlino, M Pasero Z. Kristallogr. 187 133 (1989) 223. M J Buerger, V Venkatakrishnan Proc. Natl. Acad. Sci. USA 71 4348 (1974) 224. M P Machin, P Suesse Neues Jhrb. Mineral. Monatsh. 435 (1974) 154 S V Krivovichev, S K Filatov, T F Semenova225. D G van Derveer, G H Swihart, P K Sen Gupta, E S Grew Am.Mineral. 78 195 (1993) 226. E Cannillo, F Mazzi, J H Fang, P D Robinson, Y Ohya Am. Mineral. 56 427 (1971) 227. E Bonaccorsi, S Merlino, M Pasero Eur. J. Mineral. 2 203 (1990) 228. O V Yakubovich, Yu A Malinovskii, V O Polyakov Kristallograéya 35 1388 (1990) d 229. R J Dunn, R C Rouse Am. Mineral. 70 845 (1985) 230. J Schaefer, K Bluhm Z. Anorg. Allg. Chem. 620 1583 (1994) 231.H Effenberger Monatsh. Chem. 117 1099 (1986) 232. G L Starova, S V Krivovichev, V S Fundamensky, S K Filatov Mineral. Mag. 61 441(1997) 233. G L Starova, V S Fundamenskii, S V Krivovichev, S K Filatov, in VII Soveshch. po Kristallokhimii Neorganicheskikh i Koordinat- sionnykh Soedinenii (Tez. Dokl.), Sankt-Peterburg, 1995 [The VIIth Meeting on the Crystal Chemistry of Inorganic and Coordination Compounds (Abstracts of Reports), St.-Petersburg, 1995] p. 40 234. R R Shuvalov, T F Semenova, S K Filatov, I I Bannova, in VII Soveshch. po Kristallokhimii Neorganicheskikh i Koordinatsionnykh Soedinenii (Tez. Dokl.), Sankt-Peterburg, 1995 [The VIIth Meeting on the Crystal Chemistry of Inorganic and Coordination Compounds (Abstracts of Reports), St.-Petersburg, 1995] p. 26 235. W H Zachariasen Acta Crystallogr. 2 60 (1949) 236. H A Eick Acta Crystallogr. 13 161 (1960) 237. W H Zachariasen Acta Crystallogr. 4 231 (1951) 238. P Conflant, J-C Boivin, D Thomas J. Solid State Chem. 35 192 (1980) 239. H Effenberger, R Miletich Z. Kristallogr. 210 421 (1995) 240. G B Deacon, B M Gatehouse, G N Ward Acta Crystallogr., Sect. C 50 1178 (1994) 241. T Schleid Eur.J. Solid State Inorg. Chem. 29 1015 (1992) 242. J Dugue, T Vovan, J Villers Acta Crystallogr., Sect. B 36 1294 (1980) 243. H-L Keller, R Langer Z. Anorg. Allg. Chem. 620 977 (1994) 244. A Pring, B M Gatehouse,W D Birch Am. Mineral. 75 1421 (1990) 245. R Norrestam, S Hansen Z. Kristallogr. 191 105 (1990) 246. R P Shibaeva, V I Simonov, N V Belov Kristallograéya 8 506 (1963) d 247. M B Kheirov, K S Mamedov, N V Belov Dokl.Akad. Nauk SSSR 150 162 (1963) a 248. V I Simonov, N V Belov Kristallograéya 4 163 (1959) 249. S M Skshat, V I Simonov Kristallograéya 10 591 (1965) d 250. A N Chernov, V V Ilyukhin, B A Maksimov, N V Belov Kristallograéya 16 87 (1971) d 251. E Kanillo, F Matstsi, Dzh Rossi Kristallograéya 16 1167 (1971) d 252. P Boher, P Garnier, J R Gavarri, A W Hewat J.Solid State Chem. 57 343 (1985) 253. R C Rouse, D R Peacor, P J Dunn, A J Criddle, C J Stanley, J Innes Am. Mineral. 73 643 (1988) 254. F J Ewing J. Chem. Phys. 3 420 (1935) 255. P P Reichertz, Y W Jacque J. Chem. Phys. 14 495 (1946) 256. I A Fanariotis, P J Rentzeperis Z. Kristallogr. 180 189 (1987) 257. M Gillberg Ark. Mineral. Geol. 2 565 (1961) 258. J Ketterer, V Kraemer Mater. Res. Bull. 20 1031 (1985) 259. L G Sillen, L Melander Z. Kristallogr. 103 420 (1941) 260. A M Kusainova, P S Berdonosov, L G Akselrud, L N Kholodkovskaya, V A Dolgikh, B A Popovkin J. Solid State Chem. 112 189 (1994) 261. R C Rouse, P J Dunn J. Solid State Chem. 57 389 (1985) 262. A Lagercrantz, L G Sillen Ark. Kemi, Mineral. Geol. 25 1 (1948) 263. B Aurivillius Ark. Kemi, Mineral. Geol. 26 1 (1948) 264. E I Dolomanova, V M Senderova,M T Yanchenko Dokl. Akad. Nauk SSSR 146 680 (1962) a 265. F A Bannister, M H Hey Mineral. Mag. 24 49 (1935) 266. F Pertlik, J Zemann Fortschr. Mineral. 60 162 (1982) 267. F Theobald, A Laarif, A W Hewat Ferroelectrics 56 219 (1984) 268. J Zemann Beitr. Miner. Petrogr. 5 139 (1956) 269. R W Wolfe, R E Newnham,M I Kay Solid State Commun. 7 1797 (1969) 270. V Synecek, L Zak Czech. J. Phys. 10 195 (1960) 271. R J Hill Acta Crystallogr., Sect. C 41 1281 (1985) 272. H J Riebe, H L Keller Z. Anorg. Allg. Chem. 566 62 (1988) 273. R C Rouse, P J Dunn Neues Jhrb. Mineral. Monatsch. 127 (1985) 274. C Langecker, H L Keller Z. Anorg. Allg. Chem. 620 1229 (1994) 275. Yu N Saf'yanov, R I Bochkova, V V Ilyukhin Kristallograéya 29 56 (1984) d 276. B Aurivillius Chem. Scr. 27 397 (1987) 277. V A Dolgikh, L N Kholodkovskaya Zh. Neorg. Khim. 37 970 (1992) f 278. R Restori, D Schwarzenbach Acta Crystallogr., Sect. B 42 201 (1986) 279. R Arpe, Hk MuÈ ller-Buschbaum Z. Naturforsch., B Chem. Sci. 32 380 (1977) 280. A Ferrari Gazz. Chim. Ital. 56 630 (1926) 281. B Aurivillius Acta Chem. Scand. 18 1823 (1964) 282. B Dannecker, G Thiele Z. Naturforsch., B Chem. Sci. 41 1363 (1986) 283. B Ech-Chaned, F Jeannot, B Malaman, C Gleitzer J. Solid State Chem. 74 47 (1988) 284. B Ech-Chaned, F Jeannot, B Malaman, C Gleitzer J. Solid State Chem. 86 195 (1990) 285. M A Subramanian, S Aravamudan, G V Subba Rao Prog. Solid State Chem. 15 55 (1983) 286. J Pannetier, J Lucas Mater. Res. Bull. 5 797 (1970) 287. N V Belov, A A Godovikov, V V Bakakin, in Ocherki po Teoreti- cheskoi Mineralogii (Essays on Theoretical Mineralogy) (Moscow: Nauka, 1982) p. 152 288. D A Stephenson, P B Moore Acta Crystallogr., Sect. B 24 1518 (1968) 289. O Garcia-Martinez, R M Rojas, E Vila, J L Martin de Vidales Solid State Ion. 63 442 (1993) 290. E H Kisi, M M U Elcombe Acta Crystallogr., Sect. C 45 1867 (1989) 291. G Aminoff Z. Kristallogr. 62 113 (1925) 292. R Masse, I Tordjman, A Durif C. R. Acad. Sci., Ser. 2 9 631 (1986) 293. N E Brese, M O'Keeffe, B L Ramakrishna, R B von Dreele J. Solid State Chem. 89 184 (1990) 294. C Stalhandske Cryst. Struct. Commun. 11 1543 (1982) 295. H Effenberger Acta Crystallogr., Sect. C 47 2644 (1991) 296. C T Prewitt, R D Shannon, D B Rogers Inorg. Chem. 10 719 (1971) 297. S I Okamoto, T Ito Acta Crystallogr., Sect. B 28 1774 (1972) 298. B U Koehler, M Jansen Z. Anorg. Allg. Chem. 543 73 (1986) 299. T Ishiguro, N Ishizawa, N Mizutani,M Kato Acta Crystallogr., Sect. B 39 564 (1983) 300. Yu D Kondrashev Kristallograéya 3 696 (1958) d 301. J Schaefer, K Bluhm Z. Anorg. Allg. Chem. 620 1578 (1994) 302. O Savborg J. Solid State Chem. 57 154 (1985) 303. M Wolcyrz, L Kepinski J. Solid State Chem. 99 409 (1992) 304. H Dachs Z. Kristallogr. 107 370 (1956) 305. P Mouron, P Odier, J Choisnet J. Solid State Chem. 60 87 (1985) 306. D Michel, A Kahn Acta Crystallogr., Sect. B 38 1437 (1982) 307. F Abraham, J Trehoux, D Thomas J. Less-Comm. Met. 63 57 (1979) 308. G R Facer,M M Elcombe, B J Kennedy Aust. J. Chem. 46 1897 (1993) 309. F Abraham, D Thomas Bull. Soc. Chim. Fr. 1975 25 (1975) 310. J A Hrilijac, R D Brown, A K Cheetham, L C Satek J. Solid State Chem. 84 289 (1990) 311. E N Maslen, V A Streltsov, N R Streltsova, N Ishizawa, Y Satow Acta Crystallogr., Sect. B 49 937 (1993) 312. A Bystrom, L Evers Acta Chem. Scand. 4 613 (1950) 313. M Jansen,M Bortz Z. Anorg. Allg. Chem. 579 123 (1989) 314. H Szillat, C L Teske Z. Anorg. Allg. Chem. 620 1307 (1994) 315. M Bortz,M Jansen Z. Anorg. Allg. Chem. 619 1446 (1993) 316. M Bortz,M Jansen Angew. Chem. 103 841 (1991) 317. H-J Riebe, H-L Keller Z. Anorg. Allg. Chem. 571 139 (1989) a�Dokl. Chem. Technol., Dokl. Chem. (Engl. Transl.) b�Inorg. Mater. (Engl. Transl.) c�Geochem. Int. (Engl. Transl.) d�Crystallogr. Rep. (Engl. Transl.) e�J. Struct. Chem. (Engl. Transl.) f�Russ. J. Inorg. Chem. (Engl. Transl.) Types of cationic complexes based on oxocentered tetrahedra [OM4] in the crystal structures of inorganic c
ISSN:0036-021X
出版商:RSC
年代:1998
数据来源: RSC
|
| 5. |
Rhenium-containing catalysts in reactions of organic compounds |
| |
Russian Chemical Reviews,
Volume 67,
Issue 2,
1998,
Page 157-177
Margarita A. Ryashentseva,
Preview
|
|
摘要:
Abstract. The problems in the use of rhenium compounds and supported mono-, bi-, and poly-metallic rhenium-containing catalysts for carrying out reactions involving the metathesis of alkenes and unsaturated functional compounds, the hydrogenation and dehydrogenation of hydrocarbons, the conversion of hydro- carbons and their industrial mixtures, and the hydrogenation of fractions comprising carboxylic acids and the products of the hydroformylation of synthetic aliphatic acid esters are examined.The characteristic features of the behaviour of plati- num ± rhenium/alumina catalysts under reforming conditions are described. The specificity of the action of rhenium heptasulfide in the hydrogenation reactions of condensed N-containing aro matic compounds and in the reductive C-alkylation of indoloiso- quinoline by alcohols is noted.The bibliography includes 251 references. I. Introduction Rhenium, discovered in 1925,1, 2 occupies a special place in the family of rare elements. In its various compounds, rhenium can exhibit oxidation states ranging from71 to +7. The commonest oxidation state of +7 is characteristic of compounds such as rhenic acid and its salts or rhenium heptoxide.Supported metallic and metal oxide catalysts are of great importance in heterogeneous catalysis. One of the requirements which must be met by a supported metal is its resistance to recrystallisation during the catalytic process. It is therefore useful to introduce into a catalyst a metal with a high melting point, which promotes an increase in the resistance of the catalyst to ageing.Such a metal may be rhenium, the melting point of which is 3170 8C. It is also noteworthy that the high solubility of ammo- nium perrhenate, rhenium heptoxide, and rhenium pentacarbonyl in water facilitates the preparation of rhenium catalysts by the impregnation method. A series of patents, the authors of which described the ability of rhenium to catalyse a wide variety of chemical reactions, appeared soon after the discovery of rhenium.3 The relevant data, published up to 1984, have been presented in a monograph.4 Reactions involving the hydrogenation of ethene to ethane and the preparation of methane from CO and hydrogen on rhenium-containing copper catalysts were investigated at the beginning of the 1930s.5, 6 The introduction of rhenium greatly increased their activity.It was shown in 1935 that rhenium catalysts exhibit a higher activity in the dehydrogenation of alcohols than platinum, nickel, zinc, and copper.7 An extensive investigation of the catalytic properties of rhenium and of its compounds with oxygen, sulfur, and selenium under the conditions of the liquid-phase hydro- genation of more than 100 organic compounds at an elevated pressure in a static system was carried out in the 1950s.8, 9 In contrast to the usual catalysts, rhenium oxides are capable of reducing carboxylic acids to the corresponding alcohols (ranging from ethyl to undecyl alcohol) and carboxylic acid amides to amines.Rhenium sulfides have a superior activity to that of the familiar catalysts for the dehydrogenation of alcohols to alde- hydes and ketones, such as platinum, nickel, zinc, or copper.The hydrogenation of hydrocarbons on supported rhenium ± - carbon catalysts was achieved in 1958.10, 11 The Re/Al2O3 cata- lysts showed a high activity in the conversion of C5±C7 hydrocarbons in the reforming process at elevated temperatures and hydrogen pressures.12 At the same time, at atmospheric pressure the Re/Al2O3 and Re/Al2O3 .SiO2 catalysts proved to be appreciably less active than platinum/alumina catalysts.13 The promoting effect of rhenium introduced into a palladium/ alumina catalyst was observed in 1962.14 Bimetallic (1% Re, 1% Pd) catalyst supported on Al2O3 and Al2O3 . SiO2 exhibited a high activity in the reactions of C6 hydrocarbons and in the reforming of petrol fractions,14, 15 ensuring an increase in their octane number as a result of the increase in the content of aromatic and paraffinic isohydrocarbons.The disproportionation reaction of alkenes (metathesis), which makes it possible to convert an individual alkene into two others, one of which has a higher and the other a smaller molecular mass than the initial hydrocarbon, was discovered in 1964.16 Thus ethene and butenes were obtained from propene on Re2O7/Al2O3 at 25 ± 100 8C.Rhenium behaves in this reaction similarly to transition metals such as tungsten and molybdenum. Since 1966, the disproportionation reaction has begun to be used in industry (the `triolefin' process). Information about the development of this process has been reported.17 A catalyst containing 0.01% ± 3.0% of Pt and 0.01% ± 5.0% of Re on alumina, which is active in the dehydrogenation of MA Ryashentseva N D Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii prosp. 47, 117913 Moscow, Russian Federation. Fax (7-095) 135 53 28. Tel. (7-095) 137 65 18 Received 23 June 1997 Uspekhi Khimii 67 (2) 175 ± 196 (1998); translated by A K Grzybowski UDC 546.719.541.128.13 Rhenium-containing catalysts in reactions of organic compounds MA Ryashentseva Contents I.Introduction 157 II. Catalytic properties of rhenium oxide/alumina systems 158 III. Catalytic properties of other rhenium compounds 161 IV. Catalytic properties of rhenium and its compounds on supports 164 V. Mixed rhenium-containing catalysts 170 VI.Conclusion 174 Russian Chemical Reviews 67 (2) 157 ± 177 (1998) #1998 Russian Academy of Sciences and Turpion Ltdcyclohexane to benzene and in the reforming of the petrol fraction, was patented in the USA in 1968.18 The first factory in which an effective and stable bimetallic catalyst R-16, containing platinum and rhenium supported on an oxide, began to operate in May, 1968.19 The R-16, R-19, R-22, E-500, and E-501 bimetallic catalysts were introduced into industry by the American Compa- nies Universal Oil Products, Chevron Research Co., and Engel- hard Minerals and Chemicals Co., while the process itself came to be called `rheniforming'.In our country, the Lenneftekhim Scientific-Industrial Con- glomerate (SIC) developed polymetallic rhenium-catalysts of the KRseries for the reforming process.20, 21 The first industrial batch of the KR-104 catalyst (containing 0.36% of Pt and 0.20% of Re) was prepared in 1976.The properties of improved compositions of the KR-108 and KR-110 catalysts were not inferior to the best world-class specimens. About 75% ±80% of the mined rhenium has been used for the production of various alloys, which are widely employed in electrical engineering and in electronics, aviation, rocket, and space technology.Petroleum-processing undertakings became major consumers of rhenium in 1969. They began to use it in combination with platinum as the catalyst for the reforming process.4 As early as 1978, 92% of rhenium was consumed in the USA for the production of bimetallic Pt ± Re catalysts for the conversion of petrol fractions into high-octane petrols.The importance of the employment of rhenium as the reforming catalyst has been noted at the plenary session of the International Symposium on Rhenium and Rhenium Alloys in Orlando (USA),22 which was devoted to the 70th anniversary of the discovery of this element. The development of studies on rhenium-containing catalysts used in petroleum processing and in basic and fine chemical synthesis during recent years is analysed in the present review.II. Catalytic properties of rhenium oxide/alumina systems The metathesis of alkenes reduces to the exchange of alkylidene fragments between alkene molecules: Valuable compounds, which may be used in perfumery, agriculture, and other fields, are formed in the metathesis of alkenes with functional groups.23 ± 26 Catalysts containing rhenium, molybdenum, and tungsten (Re2O7/Al2O3,MoO3/Al2O3, andWO3/Al2O3) are the most active in the metathesis of alkenes.The rhenium/alumina catalyst merits special attention because it exhibits a high activity and selectivity even at room temperature and atmospheric pressure.The meta- thesis of propene in the presence of Re2O7/Al2O3 occurs at 50 8C, whereas on MoO3/Al2O3 and WO3/Al2O3 the corresponding temperatures are 207 and 402 8C respectively.27 Catalysts con- taining rhenium with a lower valence, for example Re2(CO)10/ Al2O3, are also active in this reaction. Nowadays investigators have concentrated attention on the improvement of rhenium/alumina catalysts.Their activity in the metathesis of functional alkenes can be increased by introducing small amounts of promoting additives, for example allyl- tin,25, 26, 28 which is known as the cocatalyst in homogeneous catalytic systems. Such additives increase the effectiveness also of heterogeneous systems, initiating the formation of a metallocar- bene in accordance with the scheme One of the stages of the widely known carbene chain mecha- nism of metathesis 29 involves the formation of a metallocyclobu- tane: Rhenium/alumina catalysts containing <5% of Re2O7 exhibit a slight activity in the metathesis of alkenes.30, 31 A necessary reaction stage on these catalysts is the reduction of the carbene formed.Propene and higher alkenes are capable of reducing Re2O7 on aluminium oxide even at room temperature.32 1.The metathesis of olefins and unsaturated functional compounds The properties of the Re2O7/Al2O3 . SiO2 catalyst containing 3 mass% of Re2O7 have been investigated at room temperature in relation to the model reaction involving the disproportionation of propene to ethene and but-2-ene in a microcatalytic flow system.33 Its activity, exceeding that of Re2O7/Al2O3, was further increased on introduction of tetramethyl- and tetraethyl-tin as a result of the participation of the Brùnsted acid centres of the support in the process.The removal of surfaceOHgroups reduced the activity of the catalyst. SnR4 probably stabilises the active complex, which is especially important in the metathesis of func- tional alkenes.34 SnR4-promoted Re2O7/Al2O3, which is more active than the catalyst containing the oxides of other metals, for example MoO3, WO3, or V2O5, is used as the catalyst in this process.35 The new catalytic system Re2O7/Al2O3 .B2O3 has been tested in relation to the model reaction involving the metathesis of methyl oleate�a typical functional alkene:36 The catalysts were prepared by impregnation and partial drying at 110 8C.The amount of B2O3 introduced was 5%, 10%, 15%, and 20%. The catalyst containing 3 mass% of Re2O7 deposited on Al2O3 to which 15 mass %of B2O3 had been added exhibited the highest activity. The optimum catalyst activation temperature was 477 8C. For a reaction time longer than 1.5 h, a higher degree of conversion was achieved on this catalyst than on 18% Re2O7/ Al2O3.The added B2O3 interacts with the acid centres of Al2O3 and weakens the linkages between rhenium particles and alumi- nium oxide. When the content of deposited B2O3 is in excess of the optimum value, the amount of rhenium reduced on the surface diminishes, which lowers the activity of the catalyst. The high activity and selectivity of the low-percentage Re2O7/Al2O3 .B2O3 catalyst at room temperature has been explained by the presence on the surface of strong Brùnsted acid centres. The catalytic activity may be altered by employing various cocatalysts. The promoting effect diminishes in the series 36 SnEt45SnBu4>PbBu4>PbEt4>SnMe4 . The most active metathesis catalysts�Re2O7/Al2O3, Re2O7/ SiO2 . Al2O3, Re2O7/Al2O3 .B2O3, and MxOyRe2O7/Al2O3 (MxOy=MoO3, WO3, or V2O5) � were investigated by the temperature-programmed reduction method and thermal analy- sis.37 The rhenium particles in the Re2O7/SiO2 . Al2O3 and MxOyRe2O7/Al2O3 specimens exhibit redox properties. The pres- ence of V2O5, WO3, or MoO3 diminishes the thermal stability of the rhenium particles in the Re2O7/Al2O3 catalysts in the follow- ing sequence: Re2O7/Al2O34Re2O7/SiO2 .Al2O34Re2O7/Al2O3 . B2O3 . The unequal activities of these catalysts in the metathesis of alkenes and functional alkenes cannot be accounted for either by the different capacities of the rhenium particles for reduction, or R1R2C CR3R4 +R5R6C CR7R8 R1R2C CR5R6 +R3R4C CR7R8 . Re(CH3)2 Re CH2+CH4 . CH2+C C M +CH2 C C M C M C CH2 2Me(CH2)7CH CH(CH2)7COOMe Me(CH2)7CH CH(CH2)7Me+ +MeOOC(CH2)7CH CH(CH2)7COOMe. 158 MA Ryashentsevaby possible steric hindrance in the formation of the rhenium ¡À cyclobutane complex, or by a change in the thermal stability of the rhenium particles.36 The activity of the Re2O7/Al2O3 catalysts of the metathesis of propene increases on raising the heat treatment temperature during their preparation.38 The optimum heat treatment temper- ature depends on the Re2O7 content and is in the range 827 ¡À 927 8C. For a low Re2O7 content, the maximum heat treat- ment temperature is required. The much higher activity of the catalyst containing 3 mass%of Re2O7 has been attributed to the redistribution of the ReO4 groups on the Al2O3 surface, which has been confirmed by spectroscopic data.The catalyst heat-treated at a high temperature can be regenerated after deactivation by heat treatment at the usual temperature of 550 8C without appreciable loss of the initial activity. The strength of the Br��nsted and Lewis acid centres increases with increase in the amount of Re2O7 supported on Al2O3.39 The impregnation of a catalyst having a low rhenium content (6 mass % of Re2O7) with hydrochloric acid promotes the man- ifestation of Br��nsted acidity.With increase in the Re2O7 content, the Br��nsted acidity of the aluminosilicate gradually increases, while the Lewis acidity passes through a maximum. The activity of the Re2O7/Al2O3, MxOyRe2O7/Al2O3 (MxOy=V2O5, MoO3, or WO3), and Re2O7/SiO2 . Al2O3 catalysts of the metathesis of alkenes is directly correlated with their Br��nsted acidity, in contrast to the Lewis acidity.Thus, in order to increase the activity of low-percentage rhenium catalysts in the metathesis of alkenes, it is necessary to increase their Br��nsted acidity by introducing various modifying agents.39 After heat treatment, a monolayer containing Re7+ ions is formed on the surfaces of the Re2O7/Al2O3 catalysts.40 For a low content of rhenium, the latter enters mainly into monomeric tetrahedrally coordinated ReO�¢4 ions, while in the presence of a high rhenium content Re7O7Re linkages are formed.After interaction with the reactants, the rhenium is reduced and carbene complexes active in the metathesis are formed. The fraction of active rhenium ions is less than 1%. In the absence of cocatalysts, Re2O7/Al2O3 altogether fails to exhibit an activity in the meta- thesis of alkenes with polar functional groups.The modification of the support, for example the introduction of SiO2 into Al2O3, increases the activity of the catalyst. The addition of a third metal oxide, for example MoO3, WO3, or V2O5, increases the turnover number of the reaction for a low content of deposited rhenium.The addition of a tetraalkyltin not only increases the activity of the catalyst in the metathesis of alkenes but also makes it possible to achieve the metathesis of alkenes containing functional groups. The increase in the activity of low-percentage catalysts after their preliminary treatment with hydrogen at 500 8C and subsequent chemisorption of oxygen at 77 8C has been investigated by the temperature-programmed reduction, XPES, laser Raman spec- troscopic, and EPR methods.40 After such treatment, the signal due to adsorbed O72 ions was observed in the spectra.The active centres are formed in accordance with the scheme It has been suggested that the carbene complex is formed during metathesis as a result of the generation of acid vacancies, which is followed by reactions of the type or Catalysts such as Re2O7/Al2O3 are highly polar and therefore react with polar compounds, for example with alkenes, as well as water, which may be present in the reactants and is a catalytic poison.Molecules with polar groups are capable of blocking the free centres necessary for metathesis, for example Other possible causes of deactivation have also been discussed.40 The possibility of regenerating the 12% Re2O7/Al2O3 cata- lysts, promoted by tetrabutyltin wit2 : 4, and 3 : 4, and also of 3% Re2O7/SiO2 .Al2O3 promoted by tetraethyltin has been investigated. The metathesis of propene was carried out on these catalysts in a microcatalytic flow reactor at 20 and 80 8C and a pressure of 1.5 atm.41 The activity of the deactivated catalyst could be partially restored by increasing the content of the promoting agent and also by carrying out regener- ation in a stream of oxygen with subsequent repeated addition of the promoting agent.Nevertheless, there was a partial loss of activity after each regeneration cycle. A study of the catalyst surface by scanning electron microscopy and X-ray diffraction after the temperature-programmed reduction showed that the loss of activity is associated with the formation on the surface of the oxide SnO2, which interacts with Re2O7.The study of the reactivity of alk-1-enes in metathesis under industrial conditions over the 12% Re2O7/Al2O3 catalyst in the liquid phase 42 showed that the rate of reaction diminishes with increase in the length of the hydrocarbon chain (from hex-1-ene to dec-1-ene).It has been suggested that this is associated with the fact that the rate of reaction is determined by the desorption of the product. Alkenes with a long chain and a symmetrical disposition of the inner double bond are formed in the metathesis of higher alkenes (oct-1-ene, dec-1-ene): The reaction proceeds in accordance with the mechanism Four products D ethene, tetradec-7-ene, hexadec-7-ene, and octadec-9-ene D are formed in the joint metathesis of oct-1-ene and dec-1-ene.42 The kinetic description of the metathesis of oct-1-ene on Re2O7/g-Al2O3 in the liquid phase was based on the metallocar- bene mechanism.43 The rate-limiting stage is either the internal conversion of the carbene complex or the desorption of the product.It was not possible to make a final choice on the basis of the experimental data. The proposed mathematical model makes it possible to describe the deactivation of the catalyst as a function of the duration and temperature of the reaction. The apparent activation energy for metathesis is 22.5 kJ mol71 and that for the deactivation of the catalyst is 12.0 kJ mol71 The constancy of the degree of conversion under the conditions of the deactivation of the catalyst can be maintained by gradually increasing the reaction temperature.Calculation within the frame- work of the mathematical model showed 43 that the temperature- programmed regime makes it possible to convert a much larger amount of oct-1-ene in each catalytic cycle.The Re2O7/Al2O3 catalyst modified by the introduction of B2O3 into the support has been used for the metathesis of methyl oleate.44 The concentration of Lewis and Br��nsted acid centres O Re4+ Al3+ O2 O Re5+ Al3+ . O¡¦2 CH3 CH CH2 M CH CH2 CH2 H M CH2 CH2 M CH2 CH2 CH2 CH2 M CH2 CH CH3 M H CH CH2 CH3 . M H CH2 CH2 CH3 M (CH2)7 C OCH3 O M (CH2)7 C O OCH3 .M 2CH2 CH(CH2)nCH3 CH(CH2)nCH3 . CH2 CH2+CH3(CH2)nCH RHC M +CH2 CHR M RHC CHR CH2 CH2 . CHR+M RHC M RHC CHR CH2 CHR RHC CH2 M Rhenium-containing catalysts in reactions of organic compounds 159was determined spectroscopically during the reaction and also during the heat treatment of the support and the catalyst. When 4 5% of B2O3 is introduced, the Al2O3 and B2O3 phases are present simultaneously in the specimen, each containing surface hydroxy-groups.For a higher B2O3 content, the hydroxy-groups of aluminium oxide are fully coated by boron oxide. The number of hydroxy-groups linked to boron diminishes with increase in the B2O3 content as a result of the formation of boron-containing linear polymers. When Re2O7 is supported on B2O3-free Al2O3, the ReO4 groups react in the first place with the Lewis acid centres.If the B2O3 content exceeds 3%, then the surface hydroxy-groups are also substituted by the ReO4 groups, which increases the catalytic activity. The ReO4 groups which have reacted with the Lewis acid centres of the boronated support substitute the hydroxy-groups of the aluminium oxide during heat treatment.The hydroxy-groups of boron oxide are substituted only after heat treatment during 52 h at 550 8C. For a B2O3 content greater than 10%, the reaction of the hydroxy-groups of boron with ReO4 competes with the condensation reaction of two neighbouring hydroxy-groups. If it is supposed that the ReO4 group substituted for theOHgroup of the support is a precursor of the active centre, then the increase in the activity of Re2O7 as a result of the introduction of B2O3 into Al2O3 can be explained either by the restoration of the linkages between the strong Lewis acid centres and ReO4 or the formation of new surface hydroxy-groups, which serve as the acid centres.44 The metathesis of cyclopropane hydrocarbons with different structures, namely n-butylcyclopropane, bicyclo[4.1.0]heptane (norcarane), and 1-methyl-1-phenylcyclopropane, at 20 8C has been investigated on a 20% Re2O7/g-Al2O3 catalyst prepared by impregnating the support with a saturated NH4ReO4 solution containing tetrabutyltin.45 The reactions were carried out under an argon atmosphere, using hexane or octane as the solvent.Ethene was present in the gas phase in all cases.The liquid phase contained*1% of cyclohexene�the product of the elimination of carbene in the metathesis of norcarane: When the reaction involved bicyclo[3.1.0]hexane, ethene was also present among the gaseous products, but the liquid product did not contain cyclopentene. This has been explained by the greater tendency of cyclopentene to polymerise. C6 ±C12 mono- alkenes, including undec-5-ene (55 mass %), dodec-6-ene (35 mass %), dec-5-ene (5 mass %), nonene, octene, heptene, and hexene (*1 mass% each), were formed from n-butylcyclo- propane.The degree of conversion of 1-methyl-1-phenylcyclopro- pane into ethene was 40%. The scheme proposed for this process 46 combines the carbene chain mechanism of metathesis and the mechanism involving the formation of cyclopropane compounds: whereAand B are alkenes,Care cyclopropane compounds,Xand X0 are catalytic centres, and Y and Y0 are intermediate complexes.In the reaction involving 1-methyl-1-phenylcyclopropane, X probably represents a catalytic centre for metathesis, arising in the activation of the rhenium/alumina catalyst by tetrabutyltin.45 The interaction with a substrate molecule, accompanied by the isomer- isation of the initial hydrocarbon, is necessary for the trans- formation of X into the X0 centre: The isomerisation products may be cis- and trans-2-phenyl- but-2-enes, which apparently polymerise.Carbene may also be eliminated from the initial molecule on the centre produced, while the elimination product (a-methylstyrene) also isomerises. Thus the cyclopropane hydrocarbons isomerise on the rhenium/alu- mina catalyst and eliminate carbene with evolution of ethene, while the compounds formed polymerise or undergo metathesis.45 It has been established by the XPES method that the activity of the Re2O7/Al2O3 catalysts is determined by the reduction of Re7+ to give an intermediate oxidation state, which begins at 200 ± 300 8C.The reduction of rhenium in Re2O7/Al2O3 is known to be more difficult than in Re2O7/SiO2.47, 48 The state of rhenium in a fresh unpromoted 15% Re2O7/Al2O3 metathesis catalyst and in a specimen promoted with phenylcyclopropane has also been investigated by the XPES method.49 The rhenium in the unpro- moted catalyst exists in the form of ReO4 tetrahedra linked to the support via one oxygen atom.The promotion of the catalyst with phenylcyclopropane has been explained 49 by the appearance on the surface of fragments with a rhenium ± carbon bond in which the atomic ratio Re :C=1 : 1. Such fragments may be carbene complexes containing the Re=C double bond. The composition includes >90% of the total number of rhenium atoms in the catalyst. The high concentration of these complexes on the surface of the specimen ensures its high catalytic activity in the metathesis of hex-1-ene, which has been confirmed experimentally. 2.Metathesis of functional alkenes The metathesis of alkenes containing functional groups has been achieved on promoted and unpromoted rheniuina cata- lysts.50 ± 57 The experiments were performed at atmospheric pres- sure in a liquid-phase static system with stirring, ensuring that the reaction occurred in the kinetic region.The metathesis of allyl chloride, the allyl ether of allylcarbinol, allylbenzene, and diallyl ether 50 was achieved on catalysts supported on alumina and containing 0.5% ± 1.5% of Re with 5% or 10% of Mo or 1.5% of Re with 5% or 10% of V,50 in which the molar ratios of the initial substances and Re2O7 were 560 ± 3000 at temperatures of 22 and 55 8C.Tetrabutyltin was used to promote the catalyst. The conversion of the initial substances into the corresponding bifunc- tional or cyclic unsaturated compounds (2,5-dihydrofuran and 2,3-dihydro-a-pyran) was 15%± 20% (after 30 min) for a selec- tivity of 93%± 95%. The catalyst containing 0.5 mass%± 1.5 mass% of Re2O7 and 5 mass%± 10 mass% of MoO3 or V2O5 proved to be optimal.The structure of the alkenyl fragment in an alkenyl allyl ether influences the selectivity and rate of its metathesis.51 The reactions of allyl-, methylallyl-, and phenylallyl-carbinols and the allyl ethers of allyl-, methyl-, dimethyl-, and phenyl-carbinols have been investigated on a rhenium/alumina catalyst promoted with tetrabutyltin (15 mass% of Re2O7, 5 mass% of SnR4, and 80 mass% of -g-Al2O3) at temperatures ranging from 0 to 80 8C and for molar ratios of the initial substance and Re2O7 between 60 and 460.The reactivity of the ethers investigated depends on the structure of the alkenyl fragment. The presence of substituents at the carbon atom directly adjoining the oxygen atom retards the intramolecular metathesis. In the temperature range 20 ± 80 8C, the metathesis was characterised by a low activation energy (of the order of 10 ± 13 kJ mol71).The unsaturated cyclic ethers are formed in accordance with the scheme +CH2 CH2 . A+X [Y Y0] B+ X , C+ X0 X+ Ph Me X0 + Me H Ph Me Me H Me Ph . or R1, R2=H, CH3, C6H5. C2H4+ CH CH2 O CH CH2 +C2H4 O R1 R2 n=1 n=0 CH CH2 CH2 (CR1R2)n O CH2 CH2 CH 160 MA RyashentsevaThe intramolecular reaction predominates in the metathesis of ethers with two double bonds.51 If the hydroxy-group of o-allylphenol is converted beforehand into an ether group, it is possible to achieve a high rate of metathesis of the corresponding compound.The metathesis of o-(allyl)propoxybenzene with formation of 1,4-bis(o-propoxyphe- nyl)but-2-ene has been carried out on a rhenium/alumina catalyst promoted with tetrabutyltin at 22 8C in solvents (hexane or benzene).52 The selectivity reached 94%± 96%.It is suggested that the metathesis proceeds via the intermolecular mechanism. Aromatic alkenyl compounds can be arranged in the follow- ing sequence in terms of their reactivity in the above reaction: allylbenzene>o-(allyl)propoxybenzene>styrene. The influence of the preliminary treatment of the support on the activity of a catalyst containing Re2O7 (15 mass %), (C4H9)4Sn (5 mass %), and g-Al2O3 (80 mass %) has been inves- tigated in relation to the metathesis of n-hex-1-ene, allyl chloride, and diallyl ether.53 Treatment with water and a 0.1 N aqueous solution of hydrochloric acid increased the rate of metathesis of n- hex-1-ene and allyl chloride.This can be explained by the increase in the number of active centres of the catalyst and the increase in the acidity of the support, since an increase in acidity, especially Brùnsted acidity, promotes the metathesis of unsaturated com- pounds with a functional group.35 On the other hand, treatment of the support with ammonium hydroxide diminished the rate of metathesis. When the support of the Re2O7/g-Al2O3 catalyst was treated with trialkyl borate, which decomposes to boron trioxide, the rate of metathesis of n-hex-1-ene and diallyl ether decreased by a factor of 2.5 ± 3 compared with the initial untreated specimen.54 Thus the Re2O7 content can be increased from 10 mass%± 15 mass% to 1 mass%± 2.5 mass% without diminishing the activity of the catalyst. The maximum activity is attained for 2 mass%± 4 mass%of Re2O7 and 1 mass%± 5.0 mass%of triethyl borate.The structure of the substituent in the trialkyl borate does not affect the rate of metathesis. The degree of conversion of n-hex-1- ene on the catalyst containing 10% of (C2H5O)3B, 5% of Re2O7, 1.5% of (C4H9)4Sn, and 83.5% of Al2O3 reached 86.9% after 5 min, whereas the degree of conversion on the catalyst untreated with tetrabutyltin was 32.0% after 20 min.The rhenium/alu- mina ± boron oxide catalyst can operate in the temperature range 0 ± 48 8C. The metathesis of allyl chloride and allylacetone on a similar rhenium/alumina ± boron oxide catalyst, prepared using the ratio Re2O7 : Sn(C4H9)4=3 proceeds via an intermolecular mechanism in accordance with the equation 55 The metathesis products are dec-5-ene-2,9-dione and 1,4- dichlorobut-2-ene. As in the metathesis of n-hex-1-ene and diallyl ether, the Re2O7 content in the catalyst can be reduced from 15 mass%to 2.5 mass%± 7.5 mass%as a result of the treatment without diminishing the activity and selectivity.However, these active and selective catalysts of the metathesis of unsaturated compounds with functional groups are not sufficiently stable.54, 55 One of the causes of instability is the ability of the functional group to compete with the C=C bond for the active centres of the catalyst, i.e. the deactivation of the catalyst by the reactant.40 The introduction of variable-valence metals (Mo or V) into the rhenium/alumina catalyst makes it possible to activate it and reduce the rhenium oxide content.56 In a modification of a rhenium/alumina catalyst, both untreated and treated with SnBu4, with constant-valence metals (Na+, K+, Mg2+), its activity in the metathesis of n-hex-1-ene falls and the degree of conversion diminishes from 10.9% to 2.6%.The addition of Pd increases the activity of the catalyst containing 5 mass% of Re2O7, but its selectivity decreases from 93%± 98% to 68%± 76%. Preliminary treatment of the rhenium/alumina cata- lyst with triethyl borate 54, 55 increases its activity. The stabilising effect of aluminium oxide on rhenium appa- rently weakens with increase in the degree of its coverage by boron, which agrees with the data of another publication.36 Treatment of the support with hydrogen chloride and triethyl borate increases the activity of rhenium/alumina catalysts in the joint metathesis of 1,4-dichlorobut-2-ene and 2,3-dimethylbut-2-ene,56 so that the Re2O7 content could be reduced by a factor of two � from 15% to 7.5%.The reaction, the product of which is 4-chloro-2- methylbut-2-ene, proceeds in accordance with the equation The activity of rhenium/alumina metathesis catalysts depend on the conditions of their activation (duration and temperature of the heat treatment, the medium, etc.).57 The highest activity of the catalyst containing 5 mass% of Re2O7 is reached after its treatment at 620 ± 640 8C.The produc- tivity of the catalyst in the metathesis of allyl chloride increases by a factor of 3.After the activation of the rhenium/alumina catalyst containing 15 mass%of Re2O7, the degree of conversion of both n-hex-1-ene and allyl chloride at 580 8C increases. The activity and productivity of the catalyst can also be increased by increasing the activation time to 13 h. The rate of metathesis of n-hex-1-ene then increases by a factor of *1.5, while the productivity of the catalyst in the metathesis of allyl chloride increases by a factor of 2 ± 3.A further increase in the activation time to 20 h does not alter the activity appreciably. Yet another way of increasing the activity is the deposition of ammonium perrhenate on aluminium oxide with an intermediate heat treatment at elevated temper- atures.57 III.Catalytic properties of other rhenium compounds Metallic rhenium is known to be in most cases inferior in its hydrogenating activity to group VIII metals,4 but some of its compounds exhibit a high hydrogenating capacity. 1. Hydrogenation of organic compounds Rhenocene hydride (Z5-C5H5)2ReH manifted a high activity in the hydrogenation reactions of cyclohexene, benzene, ethyl ace- tate, and 36% acetic acid.58, 59 At a temperature of 150 8C and a hydrogen pressure PH2=100 atm, the degree of conversion of cyclohexene on a catalyst containing 0.8% of Re relative to the mass of the hydro- carbon attained 73% after 1 h in an autoclave.An increase in temperature to 180 8C made it possible to lower the amount of catalyst and the reaction time by a factor of 2 and to obtain cyclohexane in a quantitative yield.Rhenocene hydride was much more active than Re2S7 and even ReO3.59 When rhenium trioxide was used, the amount of rhenium had to be increased by a factor of 3, the reaction time had to be prolonged by a factor of 8, and the pressure had to be raised by a factor of 2 in order to attain the same activity. OC3H7 CH CH CH2 CH2 H7C3O C2H4+ CH2 CH CH2 O CH2 CH2 CH3 2 C2H4+CH(CH2)2COCH3 , CH(CH2)2COCH3 2CH2 CHCH2CH2COCH3 CH2 2CH2Cl CH C2H4+ClCH2CH CHCH2Cl .C CHCH2Cl . CH3 2CH3 ClCH2CH CHCH2Cl+CH3 CH3 C CH3 C CH3 Rhenium-containing catalysts in reactions of organic compounds 161Benzene was hydrogenated fully on rhenocene hydride at 180 8C and PH2=100 atm for a reaction time t=30 min and for a rhenium content of 1.0% relative to the mass of benzene.In this reaction too, the catalyst was much more active than ReO3. The degree of conversion of ethyl acetate (EA) in the hydro- genation reaction at 200 8C, PH2=100 atm, and t=3 h reached 60%. Under these conditions, *49% of EtOH accumulated in the catalytic reaction mixture. Under comparable conditions, the overall degree of conversion of ethyl acetate into EtOH on Re2O7 was lower by a factor of 2.It is noteworthy that platinum and palladium sulfides did not exhibit a hydrogenating activity.Ahigh activity of Re2O7 in the ethyl acetate reduction reaction has been observed:60 the yield of EtOH reached 82% at 175 8C, PH2=210 atm, and t=5 h. However, up to 6% of AcOH was formed under these conditions.The reaction proceeds in accord- ance with the equation The appreciable activity of rhenocene hydride and a fairly high selectivity of the reaction have been noted in the hydro- genation of 36% acetic acid.59 At 230 8C, PH2=120 atm and t=3 h for a Re content of 1% and for an overall degree of conversion of *86%, the yield of EtOH was *52%. Ethyl acetate was formed together with EtOH.Rhenocene hydride decomposed under the conditions indicated. The metallic phase formed exhibited an increased activity, since it was more highly disperse than bulk rhenium. The following activity series has been established for the rhenocene hydride-based heterometallic cata- lysts in the hydrogenation of acetic acid: (C5H5)2ReH >(C5H5)2ReH . AlCl3>(C5H5)2ReH .AlHCl25 (C5H5)2ReH . AlBr3 . Rhenium pentacarbonyl Re2(CO)10 also exhibits a high hydrogenating activity.61 ± 63 Cyclohexene was fully hydrogenated on this catalyst after 15 min at 230 8C and PH2=50 atm and for a Re content of 1% relative to the mass of the substrate. The hydrogenation of benzene required a higher hydrogen pressure (100 atm). In terms of its activity in the cyclohexene and benzene hydrogenation reactions Re2(CO)10 is superior to rhenium oxides 60 and is slightly inferior to rhenocene hydride.59 However, it decomposes under the conditions indicated above with forma- tion of a metallic phase exhibiting a higher activity than bulk rhenium.The lower activity of rhenium pentacarbonyl compared with rhenacene hydride can be explained by the fact that part of the metal remains bound in the form of the carbonyl.IR spectro- scopic study showed that, under the conditions of the hydro- genation of both cyclohexene and benzene, rhenium carbonyl reacts with the components of the reaction mixture. One cannot apparently rule out the possibility that not rhenium carbonyl itself but its unstable complex is catalytically active. The complex differs from the four known rhenium carbonyl hydrides � the monomeric HRe(CO)5 and the cluster compounds H3Re3(CO)12, H4Re4(CO)12 and HRe3(CO)14.It also follows from the analysis of the IR spectra that hydrogenation of benzene entails the formation of a metal carbonyl complex different from that in the hydrogenation of cyclohexene.62 Rhenium oxides with the perovskite structure and having the general formula Ba2BiIII 1=3&2/3ReVIIO6, where BIII=Y or Sm, or Ba3LaZnReVII&O12 (the symbol & denotes a vacancy in the cationic lattice) also possess hydrogenating properties.64 The catalysts were synthesised under solid-phase reaction conditions using a known method 65, 66 and were identified by X-ray phase analysis.The hydrogenation of ethyl acetate on these catalysts was carried out in a static system (in an autoclave) at 280 8C and PH2=100 atm and for t=3 h.The Ba2Y1/3&2/3ReO6 catalysts showed the highest activity: the overall degree of conversion of ethyl acetate was 35% for a selectivity in the formation of ethanol of 83.4%. After the catalyst worked for 3 h, the reaction products were removed and a fresh portion of ethyl acetate was introduced.After this, the degree of conversion of ethyl acetate into ethanol in the course of 3 h of the reaction increased from 29.2% to 43.2%. Yet another repetition of the same procedure led to a further increase in the degree of conversion from 43.2% to 47.9% (selectivity 86%). The increase in activity may be associated with the activation of the specimen in the course of the experiment by virtue of the reduction of Re(VII).The transition of rhenium to lower oxidation states in the course of the reaction was indicated by a change in the colour of the specimen from yellow or yellow- green to black. Ethyl acetate is reduced on Re2O7 even at 230 8C, whereas on the oxides described this requires 280 8C, other conditions being equal.It may be that the hydrogenating activity is determined by the presence in the catalyst not only of rhenium but also of other cations. One may postulate that the hydro- genating activity can be partly accounted for also by the formation of reduced rhenium in a highly disperse state under the exper- imental conditions. The hydrogenation of benzene and ethyl acetate has also been achieved on rhenium oxides with the perovskite structure having CH3COOC2H5+2H2 2C2H5OH.Table 1. Hydrogenation of benzene a and ethyl acetate b on rhenium oxides with the perovskite structure 67 and certain other rhenium catalysts. Catalyst Yield of Hydrogenation of ethyl acetate b C6H12 obtained composition of catalytic reaction mixture (%) conversion (%) selectivity (%) from benzene (%) a H2O EtOH ethyl acetate in EtOH overall Ba3.6Sr0.4CoRe2&O12 18 Ba3.2Sr0.8CoRe2&O12 20 Ba2.8Sr1.2CoRe2&O12 20 Ba2.0Sr2.0CoRe2&O12 22 3.9 6.9 89.1 6.6 10.6 60.6 Ba1.6Sr2.4CoRe2&O12 50 Ba1.2Sr2.8CoRe2&O12 52 5.7 13.3 81.0 12.7 19.0 67.0 Ba0.4Sr3.6CoRe2&O12 78 Sr4.0NiRe2&O12 90 8.2 10.6 81.2 10.2 18.8 54.0 Sr4.0CoRe2&O12 90 Sr4.0CaRe2&O12 0 Re2S7 3 4.0 20.9 75.1 20.0 24.9 80.3 ReO3 100 c Ba(ReO4)2 0 Ba2Y1/3&2/3 ReO6 d 4.5 30.5 65.0 29.2 35.0 83.4 Reaction conditions: a T=200 8C, PH2=100 atm, t=2 h, 1% of Re; b T=280 8C, PH2=100 atm, t=3 h, 2% of Re; c T=240 8C, PH2=100 atm, t=4 h, 3% of Re (data of Broadbent and Bartley 60); d data of Ryashentseva et al.64 162 MA Ryashentsevathe general formula A4BRe2&O12, where A=Ba or Sr and B=Co or Ni.67 The results obtained are presented in Table 1.For a rhenium content of 1% relative to benzene, the yield of cyclohexane increases from 18% to 78% as the barium content falls.64 Evidently the presence of the large barium ions (ionic radius 1.36 A) in the catalyst structure hinders the hydrogenation of benzene. Among barium-containing catalysts, the Ba0.4Sr3.6- CoRe2&O12 specimen had the highest activity under the reaction conditions (200 8C, PH2=90 ± 100 atm, Re content 1%) and the yield of cyclohexane, amounting to 78%, remained unchanged for 6 h.In the succeeding 16 h, the yield of cyclohexane fell to 35%. The Sr4.0CoRe2&O12 and Sr4.0NiRe2&O12 catalysts proved to be the most active in the hydrogenation of benzene.Benzene was virtually fully hydrogenated on these catalysts, containing 1% of rhenm, at T=200 ± 300 8C and PH2=100 ± 120 atm and for t=2 ± 3 h. The catalytic activity increased with increase in the ionisation potential of the cations A(Ba<Sr) and B(Ca<N- i<Co). The state of the surfaces of the Sr4CoRe2&O12 and Ba4CaRe2&O12 specimens before and after catalysis has been investigated by the method of thermovacuum electrical conduc- tivity curves (TVE).The specimens exhibited semiconducting properties. After the experiment on a strontium specimen, exhib- iting a high hydrogenating activity, changes were observed in the surface possibly due to its reduction. However, the specimen remained a semiconductor, i.e. there was no reduction to the metallic or pseudometallic state.The low specific surface of the specimen (1.5 m2 g71) and the presence on the surface of*12% of reduced rhenium, relative to its overall content, after catalysis (according to XPES data) made it possible to suggest that metallic rhenium is largely located not on the surface but in the bulk of the catalyst and in a highly disperse form.In order to create active hydrogenation catalysts with the perovskite structure, it is appa- rently necessary to reduce the rhenium on the surface. It has been demonstrated by the XPES method that Re4+ and Re6+ ions are present in the Sr4CoRe2&O12 and Sr4NiRe2&O12 catalysts and may enter into the composition of the active centres. The perovskites Ba2Sr2CoRe2&O12, Ba1.2Sr2.8CoRe2&O12, containing 2% of Re, and Sr4NiRe2&O12 proved to be less active and selective than Re2S7 and Ba2Y1/3&2/3ReO6 in the hydro- genation of ethyl acetate (T=280 8C, PH2=100 atm, t=3 h) (Table 1).Consequently, rhenium oxides with the perovskite structure exhibit different activities in the reactions involving the hydrogenation of the benzene ring and the carbonyl group.The hydrogenation of the latter requires more severe conditions and is more sensitive to the cationic environment of the rhenium oxides.64 2. Selective hydrogenation of N-containing condensed aromatic compounds Rhenium heptasulfide exhibits a specific activity in the hydro- genation and reductive N-alkylation by C1 ±C4 alcohols of pyridine, picoline, and lutidines.68 ± 71 It is an effective catalyst of the selective hydrogenation of aryl-substituted pyridines, isoqui- nolines, indeno[2,1a]pyridines, benzo- and dibenzo-indolizines (the reaction does not involve the benzene ring), and dihydrox- yanthracenes.In the presence of alcohols, N-alkylation takes place on Re2S7 simultaneously with hydrogenation. The results have been surveyed in a review.72 New compounds, which are of interest from the standpoint of their biological activity, have been obtained by the hydrogenation of compounds of the indolizine series 73 on Re2S7 (T=250 8C, PH2=140 atm, t=4 h).The following compounds were obtained: 2,8-diphenylperhydroindolizine from 2,8-diphenylindo- lizine, 1,2,3,4-tetrahydrobenzoindolizine and 1,2,3,4,4a,5-hexa- hydrobenzo[2,3]indolizine from benzo[2,3]indolizine, 5,6-di- hydrobenzo[2,3;5,6]indolizine and 5,6,6a,7-tetrahydrodibenzo- [2,3;5,6]indolizine from dibenzo[2,3;5,6]indolizine, 5,6-dihydrodi- benzo[2,3;7,8]indolizine and 1-benzylidene-1,2-dihydroisoquino- line from dibenzo[2,3;7,8]indolizine, 4-(4-aminophenyl)-6-ethyl- 2,3-dimethylpyridine and 4-(4-aminophenyl)-6-ethyl-2,3-dime- thylpiperidine from 6-ethyl-2,3-dimethyl-4-(4-nitrophenyl)pyri- dine, and 1,2-dihydro-, 1,4-dihydro-, and 1,2,3,4-tetrahydroiso- quinolines from 1-benzylisoquinoline. The following reactions merit special attention: The pyridine ring in benzoindolizines is hydrogenated more readily than the pyrrole ring. The presence of phenyl substituents in the indolizine does not prevent its complete reduction, while alkyl substituents hinder the hydrogenation reaction. The anne- lation of the pyrrole and pyridine rings of indolizine diminishes the degree of its hydrogenation.The nitro-group is reduced to the amino-group. The hydrogenation of bromo-substituted 6- and 7-alkyl-2-(40- bromophenyl)indolizines in the presence of Re2S7 has also been investigated.74 Under the conditions selected (T=260 8C, PH2=140 atm, t=4 h), a mixture of trans- and cis-isomers, with respect to the fusion between the pyrrolidine and piperidine rings, of bromine- free 6- and 7-alkyl-2-phenylindolizines is formed.The 6- and 7-alkyl-2-phenylindolizines isolated are characterised by a trans- fusion involving the pyridine ring in the `chair' conformation and 5,6-dihydrodibenzo- [2,3;7,8]indolizine (yield 40%) 2,8-diphenylindolizine 2,8-diphenylperhydroindolizine (yield 71%) N Ph Ph N Ph Ph N dibenzo[2,3;7,8]indolizine 5,6-dihydrodibenzo[2,3;7,8]- indolizine (yield 90%) N + N dibenzo[2,3;5,6]indolizine N 5,6,6a,7-tetrahydro- dibenzo[2,3;5,6]- indolizine (yield 16%) N R1=Et, R2=H; R1=H, R2=Me; R1=H, R2=Et; R1=H, R2=Pr; R1=H, R2=C5H11.Br N R1 R2 N R1 R2 Rhenium-containing catalysts in reactions of organic compounds 163the pyrrolidine ring in the `envelope' conformation.The nitrogen atom is located outside the plane passing through the four carbon atoms of the pyrrolidine ring. The ratio of the cis- and trans- isomers of the compounds obtained is 1 : 1.4. The hydrogenation of indolo[2,1-a]isoquinoline 1 in protic solvents (alcohols) has been achieved in the presence of Re2S7 (T=250 8C, PH2=140 atm, t=4 h).75 The N-alkylation of the initial compound observed previously 72 is ruled out owing to the presence in the molecule of a bridgehead nitrogen atom.Alkyla- tion at the C11 atom takes place instead:75 Methanol, ethanol, 1-butanol, and isopropyl alcohol were used as the alkylating agents. A mixture of compounds 2, 3, and 4 is formed in the first two instances in a high overall yield.The hydrogenation in 1-butanol leads to the formation of only the 11-butyl derivative 5 in 81% yield. If the dihydro-derivative 2 is subjected to reductive alkylation by 1-butanol, it is converted into 11-n-butyl-5,6-dihydroindoloisoquinoline 5 in a high yield. In the presence of Re2S7, the isoquinoline 1 is initially hydrogenated under the conditions indicated above to dihydroisoquinoline 2, which is subsequently alkylated with formation of the 11-alkyl derivatives of compound 5. The alkylation proceeds via an electronic substitution mechanism, the yield of products increas- ing with decrease in the acidity of the alcohol. 5,5a,10a,11-Tetrahydro-10H-indeno[1,2-b]quinoline has been obtained by the hydrogenation of 10H-indeno[1,2-b]quinoline (T=250 8C, PH2=140 atm, t=4 h) in benzene in the presence of Re2S7.Its structure was confirmed by mass-spectrometric and IR spectroscopic data, electronic absorption spectra, and 13C and 1H NMR spectra:76 The cis-fusion between the indane and tetrahydroquinoline fragments as well as the axial orientation of the proton at the C(5a) atom and the equatorial orientation of the proton at the C(10a) atom have been confirmed by molecular mechanical methods using the PC MODEL program.The possibility of hydrogenating an exocyclic double bond of the fulvene type on Re2S7 has been investigated in relation to 9-(4- pyridylmethylene)fluorene, 9-(4-pyridylmethylene)-4-azafluor- ene, and 9-benzylidene-4-azafluorene.77 The hydrogenation of 1-fulvene (T=250 8C, PH2=130 atm, t=4 h) proceeds to the extent of 90%.Three compounds � 9-(4-pyridylmethyl)fluorene 6, 9-(4-piperidinylmethyl)fluorene 7, and fluorene (the hydro- genolysis product) � were isolated from the products in 33%, 16%, and 10% yields respectively. The hydrogenation involves preferentially the exocyclic double bond of the fulvene fragment with formation of 9-azafluorenyl(pyridyl)methanes. IV.Catalytic properties of rhenium and its compounds on supports 1. Hydrogenation of benzene and ethyl acetate The dependence of the properties of supported rhenium-contain- ing catalysts on the nature of the support (a-, y-, and g-Al2O3, SiO2, Al2O3 . SiO2, MgO), the concentration of the metal (0.3 mass %, 0.4 mass %, 2.0 mass %, and 3.7 mass %) and the nature of the initial rhenium compounds [HReO4, NH4ReO4, KReO4, and Ba(ReO4)2] has been investigated.78 The degree of dispersion of rhenium, measured by the hydrogen thermal rp- tion method, was compared with the activities of the supported catalyst in the hydrogenation of benzene (flow system, T=200 8C, PH2=27.3 atm, PC6H6=2.7 atm).Before the start of the experiments, the catalysts were reduced in a stream of purified hydrogen (500 8C, space velocity vvol=15 000 h71, t=4 h). High-temperature reversible chemisorption of H2 was observed on the fresh samples. Its overall extent depended on the nature of the support and the concentration and nature of the initial rhenium compounds taken for the preparation of the catalysts.The reversible chemisorption occurred only after the attainment of high degrees of reduction of rhenium. On the other hand, if rhenium was not fully converted into the metallic state, hydrogen was absorbed at temperatures corresponding to the additional reduction temperature. The degree of chemisorption was independent of the specific surface of the support: the maximum chemisorption was observed on Re/MgO (S=94 m2 g71) and the minimum chemisorption was noted on Re/Al2O3 .SiO2 (S=370 m2 g71). When the support was impregnated with perrhenic acid, the maximum chemisorption of H2 was observed on silica gel and the minimum occurred on g-Al2O3. On g-Al2O3, the maximum chemisorption of hydrogen was attained when NH4ReO4 was employed, whereas on SiO2 the minimum chemisorption was observed on the sample impreg- nated with KReO4.The chemisorption on the catalyst obtained by impregnating aluminium oxide with a solution of the salt NH4ReO4 appreciably increased with increase in the concentra- tion of rhenium from 0.3 mass%± 0.4 mass% to 2.0 mass%± 3.7 mass %, while its further increase to 7% was accompanied by a less significant rise in chemisorption. The activity of the reduced rhenium depended on the strength of bonding of the chemisorbed hydrogen and was not correlated with the specific surface of the metal.Two regions of the thermal desorption of hydrogen were observed: at 70 ± 400 8C (form I) and at 500 ± 800 8C (form II). In order to estimate the degree of dispersion of rhenium, it is useful to employ the quantities characterising the desorption of form I.R=H (3), CH3 (4). + 2 N 5 (yield 81%) 1 N N CH3(CH2)2 CH2 CH2R N 3, 4 N N H H N H NH 7 H N 6 164 MA RyashentsevaThe activities of the Re/g-Al2O3 catalysts containing 10.4 mass%and 1.04 mass%of rhenium, subjected to a prelimi- nary treatment with hydrogen at 550 ± 800 8C (hydrogenation of benzene) or at 80 ± 300 8C (hydrogenolysis of benzene) did not change or decrease with decrease in temperature.79 A low concen- tration and high degree of dispersion of rhenium are unfavourable for both reactions, particularly for the hydrogenation of benzene.The activity of the low-percentage catalyst with an average rhenium particle size l=1.7 ± 2.6 nm was several times lower in both reactions than the activity of the high-percentage catalyst with l=3.4 ± 4.4 nm and rhenium powder with l=166 nm.80 The activity of the high-percentage catalysts in the hydrogenation reaction did not change when the average particle size was increased from 3.4 to 4.4 nm.The results obtained indicate a low activity of very small metallic particles and the presence of highly specific active centres for the hydrogenolysis of benzene.The negative influence of the decrease in the particle size of the metal on its activity in the hydrogenation of benzene has also been observed on palladium,81 ruthenium,82 rhodium,83 and nickel.84, 85 This may be associated with the enhancement of the role of the hydrogenolysis of the hydrocarbons.86 The catalytic properties of the 5% Re/g-Al2O3 system have been investigated in relation to the model ethyl acetate hydro- genation reaction.87 The principal reaction product is ethanol, while diethyl ether, hydrocarbons, and water are formed as side products. A change in temperature from 190 to 250 8C, in the hydrogen pressure from 5 to 60 atm, and in the H2 :EA molar ratio from 5 to 20 in the flow system after the catalyst had worked for 40 h did not affect its stationary activity. An increase in temperature from 250 to 270 8C did not entail an increase in the degree of conversion of ethyl acetate.The maximum degree of conversion of ethyl acetate into ethanol at 250 8C reached 40.9% for a diethyl ether content of 5.3%. It was shown that hydro- carbons are the products of the hydrogenolysis and not the dehydration of ethanol.Diethyl ether is formed from ethanol at a lower rate than from ethyl acetate. Under optimum conditions (T=230 8C, PH2=60 atm, H2 :EA=5, and vmass=0.7 h71), the degree of conversion of ethyl acetate into ethanol is 49%, while the selectivity is 83.5%. The nature of the support (y-, d-. and a-Al2O3 or SiO2) and the reduction conditions (reduction by the H2+EA mixture at 230 8C or by hydrogen at 500 8C) influence the hydrogenating properties of the supported rhenium catalyst in the conversion of ethyl acetate into ethanol 88 at 230 8C, PH2=30 atmH2 :EA=5, and vmass=0.7 h71.The following activity series was obtained: Re/y-Al2O3 > Re/a-Al2O3 > Re/d-Al2O3 > Re/SiO2 & Re/ g-Al2O3. The first catalyst of this series was three times more active than the last.Regardless of the reduction procedure, the maximum selectivity in the hydrogenation of ethyl acetate to ethanol is attained on the Re/a-Al2O3 sample. Diethyl ether is formed in measurable amounts only on the Re/g-Al2O3 and Re/ y-Al2O3 catalysts. Its formation is appreciably promoted by treatment with hydrogen. On Re/g-Al2O3, the yield of diethyl ether is 1.5 times greater than that of ethanol.After preliminary treatment with the H2+EA mixture at 230 8C, C1 ±C4 hydro- carbons are formed on all the catalysts (the maximum and minimum yields are on Re/g-Al2O3 and Re/a-Al2O3 respectively). Preliminary treatment with hydrogen at 500 8C induces a sharp decrease in the degree of conversion of ethyl acetate into hydro- carbons on the Re/g-Al2O3 and Re/y-Al2O3 catalysts.On the remaining samples, the yield of hydrocarbons as well as the selectivity in their formation change insignificantly. Rhenium(- VII), supported on SiO2 and y-Al2O3 (but not on g-Al2O3), is fully reduced by hydrogen at 500 8C. The degree of dispersion of the metal diminishes in the sequence Re/g-Al2O3>Re/ y-Al2O3>Re/SiO2. The temperature of the maximum desorption of hydrogen (200 ± 300 8C), which can participate in the hydro- genation process, diminishes in the same sequence.78 The max- imum activity of the Re/y-Al2O3 catalyst can be explained by the higher degree of dispersion of rhenium in it compared with Re/ SiO2 and the higher oxidation state of the metal compared with Re/g-Al2O3.The activity of the catalyst after preliminary treat- ment with the reaction mixture is as a rule higher than after treatment with hydrogen.This is manifested particularly strik- ingly in the case of the Re/g-Al2O3 catalyst, in which rhenium interacts strongly with the support. Hence it is reduced with greater difficulty.47 The H2+EA mixture probably reduces the supported Re(VII) more effectively at 230 8C than pure hydrogen at 500 8C.87 The kinetic data obtained suggest the possibility of the formation of diethyl ether directly from ethyl acetate.Diethyl ether is formed with participation of the acid centres on the Re/g-Al2O3 surface, on whichC2 hydrocarbons may also be formed to some extent. The absence of acid centres from the surfaces of the supports in the Re/SiO2 and Re/a-Al2O3 catalysts promotes the manifestation of a higher selectivity by the latter but a lower hydrogenating activity than in the case of Re/y-- Al2O3.88, 89 In order to discover the relation between the catalytic proper- ties and the state of rhenium in the specimens containing 0.5% of Re on g-, y-, and a-Al2O3, the kinetic data for the hydrogenation of ethyl acetate (T=230 8C, PH2=30 atm, H2 :EA=5) were compared with the results of an IR spectroscopic study of the chemisorption of carbon monoxide.90 Comparison of data obtained before and after the reaction made it possible to postulate the existence of metallic rhenium in two main states on the catalyst surface � Re0 x and Re0y , differing ithe degree of dispersion, the nature of the interaction with the support, and susceptibility to saturation by coke. On Re0 x, ethyl acetate is converted into ethanol and hydrocarbons, whilst on Re0y it is converted into ethanol and diethyl ether.On the g-Al2O3-based samples, the ionic form Ren+is also present and on it ethyl acetate is hydrogenated solely to diethyl ether. The ratio of the different states of rhenium determines their activity and selectivity in the ethyl acetate conversion reactions. The ideas described concerning the nature of the activity of rhenium/alumina catalysts for the hydrogenation of ethyl acetate are to some extent simplified. However, the observed features may prove useful for the develop- ment of more selective rhenium catalysts for the hydrogenation of carboxylic acid esters. The addition of basic oxides�lithium or lanthanide oxides� affects the properties of the 2% Re/g-Al2O3 catalyst in the hydro- genation of ethyl acetate.91 Such additives are known to diminish the acid functions of the support in the Pt/g-Al2O3 and Pd/g- Al2O3 catalysts for the dehydrogenation of alkanes and cyclo- alkanes.92, 93 The addition of 1% of lithium to the rhenium/ alumina catalyst suppresses the Lewis centres of the g-Al2O3 support, as a result of which the selectivity in the hydrogenation of ethyl acetate increases to 78%± 81% and diethyl ether is hardly formed.However, the hydrogenating activity of the catalyst and its stability diminish simultaneously (Table 2). The introduction of between 5% and 7% of the lanthanide oxide is accompanied by an appreciable decrease in the hydro- genating activity of the rhenium/alumina catalyst, while the yield of diethyl ether falls from 10.4% to 1.7% and 0.6% respectively. The selectivity in the formation of ethanol diminishes under these conditions. The maximum hydrogenating activity and selectivity was shown by the catalyst containing 2 mass% of Re, 7 mass% of a lanthanide oxide, and 91 mass% of g-Al2O3: for an overall degree of conversion of 31.2%, the activity was 81.4% in the formation of ethanol, 0.6% in the formation of diethyl ether, and 16% in the formation of hydrocarbons.The formation of hydro- carbons is apparently unrelated to the acid centres of g-Al2O3. Rhenium-containing catalysts in reactions of organic compounds 1652. Hydrogenation of halogen-containing compounds Rhenium catalysts have come to be used recently for the hydro- genation of halogen-containing compounds.A large number of various elements have been mentioned in the patent literature as catalysts for these processes: platinum group noble metals, Group VII and VIII elements, including rhenium, and certain Group II, IV, and V elements deposited on carbon. CHCl3 and CH2Cl2 may be obtained from carbon tetrachloride in a flow system, the overall degree of conversion of CCl4 amounting to 80%.94, 95 A catalyst containing515% of Cr on TiO2 and impregnated with51% of Pt, Pd, Rh, Ru and Os, Re, or Ir has been used for the hydro- genation of halogen-containing hydrocarbons.96 In the presence of metallic catalysts (Re, Co, Ni, Ru, Pd, Os, Ir, or Pt on carbon), fluoro-hydrocarbons are hydrogenated.97 In particular, CF3CHClF and CF3CH2F have been obtained from CF3CCl2F with selectivities of 11% and 87% respectively for an overall degree of conversion of 52.9%.There are data concerning the use of rhenium for the synthesis of 4-alkyl-2-fluorocyclohexanols.98 3. Hydrogenation of mixtures of oxygen-containing compounds Higher alcohols are widely used in the manufacture of lubricating oils, high-quality detergents, plasticisers, etc.The direct hydro- genation of theC10 ±C16 fraction of synthetic aliphatic acids to the corresponding alcohols at T=325 ± 375 8C and PH2=300 ± 500 atm on copper ± chromium and zinc ± chromium catalysts is therefore of special interest. However, the rhenium sulfide/alu- mina catalyst containing 1.5% of rhenium has a higher hydro- genating activity than industrial oxide catalysts.99 At 250 8C, PH2=250 atm, and v=0.13 h71, the degree of conversion of the C10 ±C16 fraction of synthetic aliphatic acids into the corre- sponding higher alcohols amounted to *80% even after the rhenium catalysts had been operating for 750 h.The hydrogenat- ing capacity of oxide catalysts falls to this level already after they have been used for 60 h.Rhenium sulfide/alumina catalysts containing 5%±8% of rhenium are not only more stable but also exhibit a higher productivity than the oxide catalysts. The results obtained using supported rhenium catalysts in the hydrogenation reactions of the products of the hydroformylation of propene,63, 100 mainly with formation of an aldehyde, merit attention.Depending on the reaction conditions, isobutyralde- hyde as well as (in amounts ranging from 10% to 20%) ethers, esters, acetals, aldols, and other oxygen-containing compounds are formed as side products. The hydrogenation of butyraldehyde is usually carried out at T=120 ± 320 8C and PH2=250 ± 300 atm in the presence of catalysts containing Co, W, Ni, Zr, Mo, Cu, and other elements in the metallic, oxide, or sulfide forms.Supported nickel and cobalt catalysts developed by various foreign companies contain at least 30% ±60% of the metal. The hydrogenation of the hydroformylation products does not consist merely in the reduction of the carbonyl group to a hydroxy-group but, since the reaction plays the main role, effective catalysts and optimum conditions are selected primarily for this reaction.When it was carried out on the hydrogen sulfide-treated 7% Re/g-Al2O3 catalyst at T=120 8C, PH2=300 atm, and v=4 h71, the content of butyr- aldehyde in the reaction mixture gradually fell from 37% to 2.3%, while the productivity of the process was fairly high.100 An increase in temperature to 140 ± 160 8C made it possible to attain a high degree of hydrogenation (98.7%) and high space velocities, up to 8.0 h71.The highest productivity (3219 g litre71 h71) was achieved at 180 8C and v=10.5 h71. The residual content of butyraldehyde was 0.5% and there were virtually no oxygen- containing compounds in the catalyst apart from butyl alcohol. The catalyst retained its high hydrogenating activity throughout five months.At T=120 ± 160 8C, PH2=300 atm, and v=4 ± 5 h71, the degree of conversion of butyraldehyde into butyl alcohol remained at the level of 99%± 100%. The hydrogen sulfide-treated bimetallic catalyst (5% Ni, 1%Re)/Al2O3 also possesses a high activity. The introduction of rhenium into the known nickel hydrogenation catalysts makes it possible to reduce its content by a factor of 6 ± 10.In terms of the degree of hydrogenation of the butyl esters of synthetic C7 ±C9 aliphatic acids, the (2% Re, 7% Ln)/g-Al2O3 catalyst is superior to the industrial copper ± chromium catalyst GIPKh-105 (flow-type apparatus, T=210 ± 218 8C, v=0.40 ± 0.45 h71, PH2=300 atm, rate of consumption of hydrogen 900 litre h71).91 On the rhenium catalyst, the esters are quantitatively converted into alcohols and the degree of conversion hardly changes throughout 450 h of continuous oper- ation.This catalyst also exhibits a higher productivity (306 ± 427 g litre71 h71) than the GIPKh-105 industrial hydro- genation catalyst (210 ± 259 g litre71 h71). 4. Hydrogenation of other organic compounds The hydrogenation of compounds of the type RCOO(CH2)n- COOH to RCOO(CH2)nCH2OH (R=alkyl, n=8 ± 16) 101 and of carboxylic acids to aromatic alcohols is carried out in an autoclave in the presence of ruthenium or Re/Al2O3 catalysts.102 On catalysts containing Ru, Rh, Pd, Pt, or Re deposited on cobalt, it is possible to hydrogenate carboxylic acids or esters.103 Lactones are obtained by hydrogenating dicarboxylic acids (saturated and unsaturated) and anhydrides in the presence of a Ni catalyst, supported on zirconium oxide or carbon, to which Group VIII noble metals and rhenium have been added.104 ± 106 Thus g- butyrolactone has been obtained in 84.9% yield in the hydro- genation of succinic anhydride in the presence of tetrrofuran on the (10% Ni, 0.9% Pd, 0.6% Re)/ZrO2 catalyst (specific surface 98 m2 g71) in an autoclave at PH2=50 atm and T=200 8C for t=3 h.104 ± 106 CH3CH2CH2CHO+H2 CH3CH2CH2CH2OH Table 2.The influence of lithium and lanthanide oxide additives on the properties of the 2% Re/g-Al2O3 catalysts in the hydrogenation of ethyl acetate (T=230 8C, PH2=30 atm, vmass=0.72 h71, H2 :EA=5, t=4 h).91 Additive Concentration of additive Yield of product (mass%) Selectivity (mass %) mass% mequiv.g71 C2H5OH (C2H5)2O C17C4 coke+losses total C2H5OH C17C4 None a 7 7 34.6 6.0 8.7 0.4 49.7 69.8 17.5 7 7 29.1 10.4 6.8 0.2 46.5 62.6 14.6 Li 0.5 0.72 23.1 1.6 4.7 0.3 29.7 77.8 15.6 1.0 1.44 21.4 traces 4.5 0.4 26.3 81.4 17.1 2.0 2.88 15.1 " 3.3 0.8 19.1 78.6 17.2 Lanthanide 5.0 0.69 24.2 1.7 5.4 0.8 32.5 75.7 16.6 oxides b 7.0 0.99 25.4 0.6 5.0 0.2 31.2 81.4 16.0 14.0 1.95 15.9 traces 2.9 7 18.8 84.6 15.4 a Re content in catalyst 5 mass %.b Composition (mass %): 28 La2O3, 49 CeO2, 18 Nb2O3, 5 Pr2O3. 166 MA RyashentsevaVinyloxirane is hydrogenated to 1,2-epoxybutane in the presence of a catalyst containing Pd and Re on BaSO4, ZrO2, or TiO2.107 Supported Group VIII metals and various rhenium com- pounds [Bu4ReO4, Re2(CO)10, Bu4NReO4, etc.] are used to obtain butane-1,4-diol by hydrogenating g-butyrolactone, maleic or succinic anhydride, or the corresponding acids.108 ± 111 For exam- ple, butane-1,4-diol has been obtained in 66.0% yield from the lactone in an autoclave in the presence of zeolites of the alkaline type or water on Pd/C and Bu4NReO4 at T=180 8C and PH2=50 atm for t=16 h.108 The reaction is carried out in a solution of NEt3 in dimethoxyethane. In the absence of NEt3, the yield is 43.2%.An even higher yield (72.5%) is attained in the presence of Pd/C and Re2(CO)10 in ethanol at T=180 8C and PH2=100 atm for t=16 h.109 Butane-1,4-diol is formed in 70.0% yield from succinic anhydride or succinic acid in the presence of Ru/C, Re2(CO)10, and a 3 A zeolite or water in dimethoxyethane (T=160 8C and PH2=100 atm, t=16 h).The reaction does not take place in the absence of the zeolite.110 Butane-1,4-diol has been obtained in 88.8% yield from succinic or maleic anhydride under similar conditions on Pt/C and Bu4N- ReO4 in Me3COH at 180 8C.111 Tetrahydrofuran has been obtained with a selectivity of 90%± 92% by hydrogenating maleic anhydride (T=250 8C, PH2=140 atm) on the (Co, Pd, Re)/C catalyst.112 On a catalyst containing rhenium, Group VIII metals, and acid components (inorganic or organic acids), deposited on a metal oxide or a zeolite, tetrahydrofuran may be obtained by hydrogenating not only maleic anhydride but also succinic anhydride or g-butyro- lactone.113 The synthesis of g-butyrolactone from water and 2,3- or 2,5- dihydrofurans in the presence or absence of hydrogen on hydro- genation catalysts, including a rhenium catalyst, at an elevated temperature has been described in a patent.114 In the hydro- genation of 2,5-dihydrofuran in the presence of water on the 6% Re/TiO2 catalyst (T=154 8C, PH2=120 atm), a mixture con- taining 85% of butane-1,4-diol, 6% of tetrahydrofuran, 3% of g-butyrolactone, 1% of 4-hydroxybutanol, and 5% of butanol is formed in one stage with a 100% degree of conversion.115 The reduction of oleic acid to octadec-9-en-1-ol (cis- and trans-isomers) has been achieved with an appreciable yield in an organic solvent on a catalyst containing Re and Sn as well as Al, Si, or Ti compounds.116, 117 The reaction was carried out in an autoclave at T=250 8C and PH2=56 atm. A new bimetallic rhenium ± tin catalyst for the reduction of oleic acid to octadec-9-en-1-ol in a satisfactory yield under mild conditions has been proposed.118 The catalyst was obtained by depositing NH4ReO4 and SnCl2 on Al2O3.Its activity and selectivity depended on the type of support, the nature of the initial compound, the molar ratio of the metals, and the conditions in the activation and the reaction itself.The hydrogenation of neocarboxylic acids leads to the for- mation of neoalcohols. For example, the corresponding alcohol has been obtained 119 from a 30% solution of pivalic acid in dioxane in a flow system on a catalyst containing 4.8% of Re and 0.5% of Pd on carbon at T=230 8C, PH2=300 atm, and v=0.15 h71. The selectivity of the reaction reached 97% for a degree of conversion of 100%.The influence of metallic promoting agents (Sn, Ge, Re) and various basic additives on the properties of Pt/SiO2 catalysts has been investigated in relation to the alkylation of sterically hin- dered anilines in the vapour phase with formation of mono-N- alkylanilines. The reaction took place with a high selectivity and activity.120 Doubly promoted Pt/SiO2 catalysts accelerate the reaction of ortho-substituted anilines with primary and secondary alcohols.This distinguishes them from the copper ± chromium catalysts, which make it possible to achieve N-alkylation by primary alcohols alone. The catalyst should be capable of activat- ing three stages: the dehydrogenation of the alcohol, the con- densation of the aniline with formation of carbonyl compounds, and the hydrogenation of the resulting imine to the final product � N-alkylaniline.When the reaction is carried out in the vapour phase, the hydrogenation stage is the most difficult. 3,5,5-Trialkyl-3-aminomethylcyclohexylamine, used to pro- duce urethane elastomers, may be obtained in 78.5% yield by the catalytic hydrogenation of 3,5,5-trialkyl-5-cyanocyclohexanone in methanol on the Co, Re, Mo catalyst in the liquid phase in the presence of ammonia at 120 8C and 80 atm.121 Diethylenetri- amine and piperazine are formed in proportions of 15 : 62 by weight as a result of the hydrogenation of ethylenediamine on a catalyst having the following composition (mass %): 6.2 Ni, 4.4 Re, and 1.8 B.122 The reaction is carried out in the liquid phase at ethylenediamine and hydrogen flow rates of 10.64 and 9.82 g mol h71 kg71 respectively and PH2=36 atm.The reac- tion time at 138.2 8C is 705 h and the degree of conversion of ethylenediamine is 6.60%. The influence of rhenium on the properties of the Pd/C catalyst in the hydrogenation reactions of o-, m-, and p-nitro- benzoic acids in an aqueous medium at 70 8C has been inves- tigated.123 ± 125 Such catalysts are resistant to poisoning by S-containing impurities in the reaction solutions.123 The reactivity of nitrobenzoic acid diminishes in the sequence para>ortho>meta on the (Pd, Re)/Al2O3 catalyst.124 The presence of rhenium as well as the texture of Al2O3 affect the state of palladium and the activity of bimetallic catalysts contain- ing 4.0% ± 4.5% of Pd and 0.9% ± 1.0% of Re in the hydro- genation of m-nitrobenzoic acid, which reacts with much greater difficulty than o- and p-nitrobenzoic acids.125 The texture of g-Al2O3 was altered by means of a hydrothermal treatment.The hydrogenation was carried out in aqueous solutions with an acid concentration of 2.461072 ± 1.361071 M at T=70 ± 90 8C, PH2=5 ± 10 atm, and a m-nitrobenzoic acid : Pd molar ratio of 2000.The addition of rhenium to the palladium/alumina catalyst increases the yield of m-aminobenzoic acid after 30 min of the reaction from 70% to 91%, while the process selectivity rises from 88% to 93%. m-Azoxybenzoic acid is formed as a side product. The introduction of rhenium prevents the sintering of the palla- dium particles, which increases the degree of dispersion of the metal.126 The hydrothermal treatment of Al2O3 alters the macro- structure of the support, makes it possible to optimise the Pt/Re ratio on the surface, and increases the content of the palladium ± r- henium groups, which, like the (Pd, Re)-clusters,127 exhibit an appreciable catalytic activity.Thus the higher activity and selec- tivity of the bimetallic systems compared with the catalyst to which no rhenium has been added is due to the increase in the degree of dispersion and in the thermal stability of palladium.As a result of the alteration of the macrostructure of the support during the hydrothermal treatment, the Pd/Re ratio on the catalyst surface decreases from 4 : 1 to 1 : 1. 5.ehydrogenation of hydrocarbons The dehydrogenation of n-dodecane 128 ± 130 and cyclohexane 131 has been achieved on supported rhenium-containing catalysts. Comparison of the activities of the 0.5% Re/Al2O3 and 0.5% Pt/ Al2O3 catalysts in the dehydrogenation of n-dodecane (T=480 8C, PH2=2.5 atm, vvol=50 h71, C12H26 :H2=8) showed that the yield of monoalkenes is 18.6% on the former catalyst and 12.1% on the latter.The selectivities in the formation of n-monoalkenes for degrees of conversion of 23.2% and 24.8% were 80% and 49% respectively. However, as a result of contact with air after the reduction of the rhenium catalyst at 900 8C and its cooling in hydrogen to 20 8C, the yield of monoalkenes fell from 9.8% to 4.4%. It was observed that preliminary treatment with hydrogen at 700 ± 900 8C influences the activity of the rhenium/alumina catalyst.128, 129 A similar effect, induced by the preliminary high-temperature treatment with hydrogen (900 8C, 3 h), was observed also when the 0.25% Re/Al2O3 catalyst was employed. After treatment at 600 8C, the selectivity in the formation of monoalkenes fell from 91% to 84% and their yield decreased from*16% to *15%.A Rhenium-containing catalysts in reactions of organic compounds 167decrease in the concentration of rhenium to 0.1% and preliminary treatment with hydrogen at temperatures ranging from 700 to 900 8C increased the dehydrogenating activity and diminished the isomerising and cracking activities and there was an increase in selectivity. The selectivity in the formation of monoalkenes on catalysts containing 0.2% and 0.5% of rhenium also increased after the preliminary heat treatment of the support (Al2O3) in air at 900 8C.127 The preliminary treatment with hydrogen of the (0.2% Re, 0.2% Pb)/Al2O3 bimetallic catalyst at 700 ± 900 8C instead of the usual temperature of 500 8C also had a positive effect.128 The yields of n-monoalkenes formed from n-dodecane were respec- tively 5.4% and 12.4% after treatment with hydrogen at 500 and 700 ± 900 8C, while the productivity of the catalyst was 2.5 and 8.3 g of n-monoalkenes per gram of the catalyst per hour.The selectivity remained at a high level (93%) in both cases. Iron has a positive effect on the dehydrogenating activity of the rhenium/alumina catalyst.130 The catalyst obtained by depos- iting NH4ReO4 on the Fe(NO3)3/Al2O3 system heat-treated beforehand in air showed the highest activity in the dehydrogen- ation of n-decane and n-dodecane (T=480 8C, PH2=2 ± 2.5 atm, vvol=35 ± 80 h71, molar ratio hydrocarbon : - hydrogen=8).The degree of conversion of n-dodecane may be increased by a factor of 2.5 ± 3 if the catalyst is subjected to a preliminary treatment with hydrogen at 500 ± 800 8C.The activity of the resulting catalyst is higher than that of the (Pt, Re)/Al2O3 specimen prepared similarly and reduced with hydrogen at the normally employed temperature of 500 8C. The dependence of the activity of the catalyst on the temperature of its preliminary treatment with hydrogen in the range from 500 to 900 8C passes through a minimum in the region of 600 ± 700 8C.The promoting effect of iron on rhenium is manifested for low iron contents. At an iron concentration of 3 at. %, the degree of conversion of n-dodecane increases by a factor of 1.7 ± 2.0 if the preliminary activation of the sample with hydrogen is carried out at 900 8C and not 500 8C. However, for an iron content of 5 at.% and a reduction temperature in excess of 700 8C, the promoting effect vanishes. The highest degree of conversion is attained if the rhenium content is 0.25 mass %.Modification with iron makes it possible to reduce by 150 ± 200 8C the temperature at which the same effectiveness in the conversion of n-alkanes is reached as on the monometallic Re/ Al2O3 specimen. It has been suggested 128 that, in order to over- come the strong interaction between the metal, activating the C7H bond in alkanes, and the support, it is necessary to reduce the metal to the zerovalent state.The formation of the Re0 active centres on the Al2O3 surface is favoured by reduction at a temperature above 700 8C and, in the case of bimetallic catalysts, by the deposition of a compound of the active metal (by impreg- nation with NH4ReO4) on the modified Fe/Al2O3 supports subjected to preliminary thermal oxidation.The state of rhenium in the 0.25% Re/Al2O3 catalyst reduced with hydrogen at 500 ± 900 8C has been studied by analysing the diffuse reflection IR spectra of adsorbed CO.131 Together with ionic forms of rhenium (+1 and +4 oxidation states), a highly disperse (possibly two-dimensional) metallic phase, the electron- donating capacity of which is reduced as a result of a strong metal ± support interaction, is present on the surface. The CO adsorbed in a linear form on such a metal is removed by evacuation even at 20 8C.The amount of the highly disperse metallic phase on the support surface increases monotonically with increase in the activation temperature.The activity of the catalyst in the n-dodecane dehydrogenation reaction varies in parallel with the concentration of the electron-deficient highly disperse metallic phase. On this basis, it has been concluded that the highly disperse Re0 formed during the high-temperature treatment in a stream of hydrogen is a precursor of the catalyti- cally active centres for the alkane dehydrogenation reaction.The dehydrogenation of cyclohexane to benzene (T=350 8C, v=0.5 h71) on a rhenium catalyst in which sibunit [a granulated pyrocarbon, bulk density 0.6 g cm73, Ssp (with respect to N2)=680 m2 g71, Ssp (with respect to phenol)=230 m2 g71] was used as the support, proceeds at a higher rate than on the catalyst obtained by depositing rhenium on g- and y-Al2O3.132 On the catalysts containing 2% of Re supported on sibunit, g-Al2O3 and y-Al2O3, the overall degrees of conversion of cyclohexane into benzene were 32.4 mass %, 15.2 mass %, and 9.7 mass%respec- tively.The selectivity of the catalysts at 350 8C diminished in the sequence Re/y-Al2O3>Re/sibunit>Re/g-Al2O3. With increase in the reaction temperature to 400 8C, the selectivities for the formation of benzene on the same three specimens were respec- tively 37.9%, 42.4%, and 16.8%.Evidently, the Re/sibunit catalyst is more sensitive to an increase in temperature than the catalysts on aluminium oxide. The dehydrogenating activity of the 2% Re/sibunit catalyst prepared using HReO4 is higher by a factor of 1.3 than in the case where NH4ReO4 is employed.This has been attributed to the greater ease of the reduction of the Re(VII) formed from perrhenic acid. In contrast to the rhenium oxide catalyst, there is no strong interaction between the metal and the support in the rhenium ± carbon system. The dehydrogenating activity of the catalyst is influenced by the oxidative treatment of the support with nitric and oxalic acids.After treatment with 13% nitric acid for 1 h, the selectivity of the 2% Re/sibunit catalyst (T=400 8C, v=0.5 h71) increased from 35.2% to 61.7%. This may be explained by a decrease in the particle size of the reduced rhenium. Preliminary addition of oxalic acid to the support has a stronger effect on the sibunit catalyst than on the y-aluminium oxide catalyst. The selectivity in the conversion of cyclohexane into benzene on the2%Re/sibunit catalyst for an overall degree of 40% rose from 42.2% to 51.1%, i.e.by a factor of 1.35, whereas on the 2% Re/y-Al2O3 catalyst the increase was from 50.5% to 61.2%, i.e. by a factor of 1.2. 6. Reactions with participation of CO, CO2, and H2O Supported rhenium-containing catalysts have been used also in the hydrogenation of CO2 to methanol,133 which can proceed via the intermediate formation of CO.The rate of hydrogenation of CO on the Re/ZrO2 catalyst is higher than on Re/CeO2. In order to elucidate the reaction mechanism, a study was made of the conversion of formic acid and formaldehyde in the presence of hydrogen using 13C as a tracer. It was shown that the surface formaldehyde participates in the methanol formation stage.In contrast to the Co/SiO2 and Re/SiO2 catalysts the com- bined (Co, Re)/SiO2 catalyst is active in the hydrogenation of CO to ethanol and hydrocarbons.134 The introduction of strontium into the bimetallic system diminishes the yield of the hydro- carbons and increases the selectivity in the formation of the alcohol from 10% to 25%. It has been demonstrated by physical methods that strontium controls the reduction of Co2+ to Co0 and that the basic active centres of the catalyst contain highly disperse metallic cobalt.Rhenium promotes the reduction of Co2+ to Co0. The (Co, Re, Sr)/SiO2 catalyst was prepared by employing cobalt acetate. If Co(NO3)2 or CoCl2 is used to prepare the sample, then rhenium has no modifying effect on the hydrogenation of CO to methanol.135 The use of CoCl2 has a particularly negative effect on the formation of methanol.Rhenium promotes the reduction of Co2+ to the metal, facilitating the hydrogen spill over. The addition of promoting agents (Re, Ru, Ir, Rh, Pt or Os) to the Co/SiO2 catalyst obtained from Co2(CO)8 did not alter its activity in the CO hydrogenation reaction.136 An attempt has been made to use rhenium catalysts for the partial oxidation of methane by the oxygen in synthesis gas (T=1000 8C, v=100 000 h71), but they were rapidly deacti- vated as a result of the volatilisation of the metal in the form of oxides.137 Together with other metals (Ru, Rh, Ir), rhenium has been used as the catalyst of the reaction of methane with CO2.138 At 777 8C, the degree of conversion of methane on the Re/g-Al2O3 system reached *85%.However, at lower temperatures the activity of the rhenium catalyst diminished sharply. Thus at 500 8C the degree of conversion of methane was <5%. The 168 MA Ryashentsevaauthors explained this effect by the catalytic oxidation of the metal surface. The characteristic features of the reduction of CO2 under the conditions of the thermoprogrammed reaction have been inves- tigated on the 3% Re/Al2O3 catalyst.139 The rate of reaction increases sharply after the reduction of the catalyst and also as a result of the interaction ofCO2 with carbon fragments on addition of 1%±2% of hydrogen.It has been suggested that formate is formed as an intermediate in this process and that hydrogen has an initiating effect. At high hydrogen concentrations in the CO2+H2 mixture, the conversion of carbon dioxide leads to the formation of CO and CH4.The addition of formic acid to the reaction mixture increases the rate of formation of methane. It may be that the conversion of CO2 proceeds via the formation of intermediate formate fragments, bypassing the CO2 dissociation and CO hydrogenation stages.The reduction of CO2 includes a stage in which surface carbonates are produced. The acceleration of the Boudouard reaction (CO2+C 2CO) has been observed on the 3% Re/Al2O3 catalyst in the presence of small amounts of hydrogen,140 where it was less pronounced than on the 8% Fe/Al2O3 system. In the presence of the previously coke-saturated (in the isobutane conversion reac- tion) 3% Re/Al2O3 catalyst, the conversion of CO2 under the conditions of thermoprogrammed heating occurred only at tem- peratures above 640 8C and the rate of formation of CO was low.The addition of 1%±3% of hydrogen to the stream of CO2 induced a sharp acceleration of the reaction. The rate of con- version of CO2 increased by a factor of 25, while the coke oxidation temperature fell by 200 8C.The activation energy for the formation of CO also decreased. The maximum rate of formation of CO was attained at 800 8C, while a further increase in temperature led to a decrease in rate. Under the conditions of thermoprogrammed cooling, the rate of conversion of CO2 at temperatures below 800 8C was significantly higher than at the analogous temperatures under heating conditions.The authors explained this effect by a heterogeneous-chain mechanism of the reduction of CO2 by rhenium or iron during the occurrence of the Boudouard reaction. The reaction CO2+H2 CO+H2O takes place at similar hydrogen and CO2 concentrations. It has been suggested that, when a heterogeneous-chain mechanism operates, ReHCOO is formed as an intermediate complex.Thus the higher reactivity of CO2 compared with CO in hydrogenation reactions can be accounted for by the formation of intermediate active species in which the dissociation of the C7O bond is facilitated.139 Together with other additives, rhenium improves the proper- ties of Fischer ± Tropsch catalysts containing 12%± 20% of cobalt.141 Vada et al.142 added 1.0 mass% of Pt or Re to the catalyst containing 8.7% of Co and 91.3% of Al2O3 and carried out the hydrogenation of CO on it (T=200 8C, PH2=5 atm, and H2/CO=2 or T=220 8C, PH2=1 atm, and H2/CO=7.3).The introduction of Pt or Re appreciably increased the rate of reaction referred to unit mass of cobalt. The selectivity did not change under these conditions. The increase in the rate of reaction was induced by the fact that Pt and Re facilitate the reduction of Co atoms and increase their surface concentration.The promoting effect of rhenium on the cobalt catalyst for the Fischer ± Tropsch synthesis has been investigated by diffuse reflection IR spectroscopic methods.143 Here it was also shown that rhenium promotes the reduction of cobalt. Rhenium is initially located in the surface layer and most probably forms the tricarbonyl.Supported rhenium-containing catalysts are also used for the conversion of hydrocarbons by reaction with steam. In terms of activity and selectivity in the conversion reactions of hydrocarbons with water vapour at temperatures above 600 8C, the 7% Re/g-Al2O3 catalyst is not inferior to the industrial nickel-containing catalyst GIAP-3.144 The following reactions take place under these conditions: Later the same investigators studied the activity of the Re/ g-Al2O3 catalyst containing 3% and 7.5% of rhenium in the conversion of isobutane by reaction with water vapour in the presence of the CS2 catalytic poison.145 The process was carried out in apparatus of the flow and flow-circulation types at atmospheric pressure. On the 3% Re/g-Al2O3 catalyst at T=700 8C and vvol=1500 h71 and for a steam/isobutane ratio of 12, the addition of CS2 in amounts corresponding to sulfur contents of 4 and 30 mg per m3 of gas reduced the overall yield of the conversion product (H2, CO, CO2) from 95.7 vol.% (in the absence of sulfur) to 89.3 vol% and 89.4 vol% respectively.The introduction of 300 mg m73 of sulfur not only reduced the content of H2, CO, and CO2 in the effluent gas but also led to the appearance of hydrocarbons with a lower molecular mass than that of the initial substance, including ethene and propene.The increase in the rhenium content from 3% to 7.5% did not improve the resistance of the catalyst to poisoning by sulfur. The (Re, Co)/Al2O3 and (Re, Ni)/Al2O3 bimetallic catalysts have also been used for the conversion of isobutane.146 The introduction of cobalt (3%) into the 1% Re/g-Al2O3 catalyst lowered and the introduction of nickel (3%) increased its activity and selectivity in the formation of H2, CO, CO2, and CH4.In contrast to the 3% Ni/g-Al2O3 catalyst, the bimetallic catalysts containing 1% of Re and 3% of Ni on g-Al2O3 ensured the full conversion of isobutane even at 500 8C.The gas formed had a nearly equilibrium composition, whereas in the presence of the industrial catalyst GIAP-3 as well as the nickel/alumina catalyst deviations from equilibrium towards the predominance of methane were observed. With increase in temperature, the com- positions of the gas obtained on all three catalysts approached one another. 7. Oxidative dehydrogenation and acetoxylation reactions The oxidative dehydrogenation of cyclohexane and ethylbenzene on rhenium-containing oxide systems has been investigated.147 In the absence of air and water, the 2% Re2O7/g-Al2O3 and 2% Re2O7/y-Al2O3 catalysts exhibited a low activity: the degree of conversion of cyclohexane at 420 8C was only 0.5% and that of ethylbenzene was 4% at 500 8C.In the presence of oxygen, the effectiveness of the dehydrogenation of cyclohexane was higher by a factor of 10 ± 30. In the oxidative dehydrogenation of ethyl- benzene without the addition of water vapour, the activity of the catalysts increased by an order of magnitude. In the course of half an hour, the degree of conversion of ethylbenzene into styrene reached 52% for a selectivity of 90% and then remained constant.The modification of binary magnesium-containing oxide systems by the addition of Re2O7 increases the activity of the catalyst. The optimum catalyst for the oxidative dehydrogenation of ethylbenzene proved to be the system incorporating V2O5 (11.2%), Re2O7 (1.2%), and MgO (87.6%). The degree of conversion of ethylbenzene into styrene on this sample was higher than on the binary system and some suppression of the extensive oxidation processes was achieved.In the presence of an excess of atmospheric oxygen (molar ratio styrene : oxygen=1 : 1.5 ± 2), the yield of styrene at 500 8C was 70% for a selectivity of 87%± 88%. An increase in temperature to 540 8C led to an appreciable rise in the degree of extensive oxidation.The addition of Re2O7 to the V±Mg binary oxide system apparently intensifies the dehydrogenating function of the catalyst. The gas -phase oxidative acetoxylation of propene to allyl acetate has been achieved on supported Pd and Pd, Re cata- lysts.148, 149 The reaction was carried out at atmospheric pressure, 180 8C, and a rate of supply of the acid of 2 h71 using the ratios C3H6 :AcOH:O2=2 : 1 : 0.5.The high-silica zeolite TsVM iso-C4H10+4H2O iso-C4H10+8H2O 4CO+9H2, 4CO2+13H2. Rhenium-containing catalysts in reactions of organic compounds 169(SiO2 : Al2O3=29.6),148 g-Al2O3, and Al2O3 . SiO2 were used as supports.149 The activities of the 1.5% Pd/TsVM and (1.5% Pd, 1.5% Re)/TsVM catalysts were 5.8961073 and 9.0661073 mol g71 h71 for selectivities of 81% and 83% respec- tively.The introduction of rhenium increased the activity by a factor of 1.5. The activity of the (Pd, Re)/zeolite catalyst was influenced by the concentration of rhenium, the order in which it was introduced, and the composition of the initial perrhenate [NH4ReO4, KReO4, Ba(ReO4)2, or HReO4]. The bimetallic catalyst with the ratio Pd : Re=1, prepared from ammonium perrhenate, had the highest activity.The introduction of 0.5% ± 0.7% of Re into the 0.7% Pd/Al2O3 . SiO2 catalyst increased its activity without altering the selectivity (*80%). A further increase in the rhenium concentration to 1%± 1.5% diminished the activity and selectivity of the catalyst. The higher activity of the bimetallic catalysts, obtained as a result of the introduction of rhenium after the reduction of palladium, com- pared with the monometallic palladium sample, may be due to the interaction of rhenium oxides with the support surface, which depends on the degree of dehydroxylation of the surface.150 V.Mixed rhenium-containing catalysts 1. Reactions of hydrocarbons The principal reactions of the reforming process are dehydrogen- ation, aromatisation, isomerisation, and hydrogenolysis.The properties of many rhenium-containing catalysts have been inves- tigated in relation to these reactions. The (Pt, Re)/Al2O3 bimetallic catalysts, prepared by precip- itation, were investigated in the propane dehydrogenation reac- tion.151 The (Pt, Re)/Al2O3 sample proved to be less active and selective in relation to the formation of propene than (Pt, Sn)/ Al2O3.The hydrogenolysis of n-butane on Pt/Al2O3 catalysts involves the formation of adsorbed carbon particles, which influence the proportions of the products obtained.152 The centres responsible for the dissociation of the central C7C bond are poisoned preferentially. Such species are not adsorbed on the (Pt, Re)Al2O3 catalysts.The (Pt, Re)/Al2O3 catalyst proved to be less active under n-heptane reforming conditions than (Pt, Ir)/Al2O3 owing to cracking, which intensifies if the reduction takes place in the presence of water.153 In order to facilitate the aromatisation of C6 andC7 alkanes on the Pt, Re reforming catalyst and to increase the selectivity of this reaction, it has been recommended that platinum deposited on the L-zeolite be introduced into the catalyst.154 The catalyst is obtained by the mechanical mixing of the standard reforming catalyst with Pt/L-zeolite.The aromatisation of n-hexane under reforming conditions using rhenium- and platinum-containing catalysts in proportions of 1 : 1 and 2 : 1 has been investigated.155 Hydrogen has only a weak influence on the dehydrocyclisation of hexane to benzene. With increase in pressure, the selectivity of the reaction dimin- ishes, which intensifies the isomerisation of n-hexane.However, this has little effect on the activity of the catalyst. The deposition of coke on both catalysts diminishes with increase in pressure and the H2 :C6H14 molar ratio. On the catalyst with Re : Pt=2 : 1, the extent of the deposition of coke was much smaller than on the catalyst with the 1 : 1 composition.The activity of (Pt, Re)/Al2O3 catalysts depends on the method used for their preparation (joint or successive impregna- tion) and on the reduction procedure (direct reduction after the deposition of the metal, heat treatment with subsequent reduc- tion).156 Heat treatment appreciably diminishes the metal ± metal interaction, which is indicated by the results obtained in the study of the hydrogenolysis of cyclopentane. Sulfiding of the catalysts increases their activity in the n-heptane dehydrocyclisation reac- tion.The dehydrocyclising capacity of the Pt/Al2O3 and (Pt, Re)/ Al2O3 metal cluster catalysts has been investigated in relation to the conversion of n-heptane into toluene under conditions close to those in reforming (T=500 8C, PH2=12 atm).157 Platinum ± r- henium metal cluster catalysts exhibited a higher selectivity and stability than the samples obtained by impregnating aluminium oxide with an aqueous solution of the initial platinum and rhenium compounds.The carbonyl complexes were decarbonised with formation of carbon particles and CO2.The increased activity of the catalyst was associated with the formation on their surface of highly disperse carbon particles. The metal cluster Pt, Re catalysts were more stable than the analogous Pt catalysts and the standard (Pt, Re)/Al2O3 reforming catalysts. The addition of boron and tin to the Pt/Al2O3 and (Pt, Re)/ Al2O3 catalysts influences the activity of the latter in the dehydrogenation of cyclohexane, the dehydroisomerisation of methylcyclopentane, and the hydrocracking of 2,3-dimethyl- butane.158 In order to eliminate alkenes from the reforming products, they are subjected to selective hydrogenation on a catalyst containing (mass %) 0.05 ± 0.15 Pt, 0.001 ± 0.05 Cd and/or 0.01 ± 0.1 Re, and 0.01 ± 0.1 Sb on g-Al2O3.159 Group VIII metals (Pt, Rh, and Ru) supported on Al2O3 .- TiO2 exhibit a high activity in the benzene, naphthalene, and biphenyl hydrogenation reactions at 300 8C and PH2=65 atm.160, 161The activity of these catalysts increases after the addition of a second metal (Ir, Re, Pd). The bimetallic catalyst exhibits an enhanced resistance to poisoning by sulfur, the source of which may be thiophene.The activity of bimetallic catalysts on the TiO2 support increases as a result of dispersion in combination with the addition of high-valence cations, for example W6+. The bimetallic catalysts have a hydrogenating activity an order of magnitude higher than the usual hydrogenation catalyst (Co, Mo)/Al2O3. In the study of the selective hydrogenation of o-xylene on metals deposited on SiO2 (Pd, Ir, Pt, Ru, Os, Ni) in combination with rhenium, a correlation was observed between the electronic conductivity of the metal and the selectivity of the catalyst in relation to the formation of the cis-product.162 The influence of heat treatment on the reactivity and selectivity of the bimetallic catalysts was noted. 2.The influence of chlorine, sulfur, and coke on the properties of the bimetallic catalysts Chlorine and sulfur are known to be active modifying agents for supported Pt, Re catalysts for the conversion of hydrocarbons and the reforming of petrol fractions.The promotion of the (0.3% Pt, 0.3% Re)/Al2O3 catalyst was investigated by temperature-pro- grammed reduction methods (TPR), analysis of the fine structure of X-ray absorption spectra (EXAFS), X-ray absorption near- edge structure spectroscopy (XANES), the oxygen adsorption method, and IR spectroscopy of adsorbed CO.163, 164 It was found that the presence of chlorine promotes the formation of a Re4+-containing phase in the course of the preliminary treatment of the catalyst at 450 8C.This phase interacts strongly with the surface layer of Al2O3 , which prevents the formation of the Pt ± Re alloy on reduction of the species, the specific role of chlorine in the interaction of the metal with the Al2O3 support has also been confirmed by other results.165 In the absence of chlorine, such interaction may be fairly intense, but, when a solution of chloroplatinic acid is deposited, the surface hydroxy- groups are replaced by chloride ions and a stable metal-supported complex is formed. It has been confirmed by the TPR and XANES methods that the chloride present on the Al2O3 surface plays the main role in the formation of an alloy between Pt and Re during the reduction process.166 The rhenium on the Al2O3 surface (tentatively in the form of an oxide) is mobile.In the presence of sulfur, the activity of the Pt, Re catalyst in the hydrogenation ± dehydrogenation reactions falls, The irreversibly adsorbed sulfur binds the entire rhenium in the form of Re2S and *10% of platinum in the form of Pt2S.With increase in the fraction of rhenium, the undesirable sensitivity of the catalyst to sulfur increases. 170 MA RyashentsevaRhenium, particularly in the form of the alloy with platinum, is a very active hydrogenolysis catalyst.167 Sulfidation may decrease the activity of this catalyst to zero, since sulfur covers the rhenium surface.The sulfur compounds of rhenium them- selves are incapable of accelerating the hydrogenolysis of hydro- carbons and act merely as diluents of the platinum. The addition of sulfur increases the resistance of the platinum catalyst to deactivation, but the adsorbed sulfur is rapidly lost.The intro- duction of rhenium influences the selectivity of the catalytic system, because it induces modification of the active centres of platinum and promotes the retention of sulfur on the surface. The probability of effecting reactions in which large ensembles of platinum atoms participate (hydrogenolysis, dehydrocyclisation, isomerisation, and cyclisation) diminishes as the latter are reduced.However, the alloying of platinum with rhenium does not influence the initial rate of hydrogenolysis. Small ensembles of platinum atoms, formed on dilution of platinum by sulfur compounds of rhenium, are resistant to poisoning by carbon deposits, since there is no space on the catalyst surface for a large polymeric carbon structure to grow.Such a catalyst is very stable until the adjacent Pt, Re, S moieties lose their sulfur. The reactions of cyclohexane and n-hexane have been inves- tigated at 297 ± 467 8C on platinum catalysts in which the support was a rhenium foil with an overall surface area of 0.5 ± 1.0 cm2.168 The surface was sulfided before the reaction and under the reaction conditions by adding thiophene to the hydrocarbon.The ReS formed is catalytically inactive and only the dehydrogen- ation and hydrogenation reactions occur in the system, but the catalyst becomes more resistant to deactivation. The problems of the deactivation of the (Pt, Re)/Al2O3 reforming catalysts by coke and sulfur have attracted the attention of investigators, since stability is one of the most important requirements which must be met by industrial catalysts.The content of residual coke, deposited on the (Pt, Re)/Al2O3 catalyst during the reforming of petroleum in the temperature range 350 ± 650 8C has been determined.169 The residual coke was investigated by the temperature-programmed oxidation method, X-ray diffraction, IR spectroscopy, chromatograph-linked mass spectroscopy, NMR, electronic spectroscopy, EPR, and chemical analysis.After the coke had been burnt away at 400 8C, the residual deposits were characterised by a minimalH:C ratio and a maximal concentration ofC=Ogroups. At low temperatures, the most hydrogenated and amorphous carbon particles are the first to burn. At a high temperature, the combustion is nonselective and all the deposits burn simultaneously.In the course of combustion, coke is partly oxidised and intermediate species containing the C=O and C7OH groups are formed. The effects of coating with rhenium and sulfidation of the surface of the platinum reforming catalyst have been investigated in relation to the reactions of n-hexane and cyclohexane on platinum without a support under the conditions of ultrahigh vacuum.170 In the absence of sulfur, the degree of cyclisation of n-hexane diminished with increase in the rhenium content.The introduction of sulfur decreased the hydrogenolysis and increased the cyclising activity. The maximum cyclising activity of the sulfided catalyst was observed when the surface was coated by a monolayer of rhenium.Similar results have also been obtained under the conditions of the reactions of cyclohexane on the surface of the bimetallic Pt, Re catalyst: after sulfidation, the contribution of hydrogenolysis diminished, while that of dehydrogenation increased. The maximum rate of hydrogenation was attained on the sulfided catalyst with the platinum coated by 0.5 of a rhenium monolayer.A multiflow reactor, which makes it possible to determine the composition of the gas phase along the catalyst bed and the coke deposition profile, has been used to investigate the deactivation of the Pt/Al2O3 and (Pt, Re)/Al2O3 catalysts in the reforming of n-heptane.171 At a low pressure (1.05 atm), the coke content on the Pt catalyst increased, while at a high pressure (12.25 atm) it fell.The maximum deposition of coke was observed at an intermediate pressure. Correlations were noted between the coat- ing of the surface by coke and the formation of C5 naphthenes and also between the changes as a function of time in the supply of the starting material, pressure, and the location of the section on which coke is deposited. The C5 naphthenes are apparently the main source for the formation of coke deactivating the catalyst.The addition of rhenium influences the deposition of coke and the formation of C5 naphthenes. The form of the temperature- programmed oxidation (TPO) spectrum depends on the pressure at which the coke is deposited. An increase in the overall pressure leads to identical changes in the TPO spectra on the Pt and Pt, Re catalysts. The results confirm that rhenium increases the surface concentration of hydrogen on the Pt, Re catalyst and hence diminishes its dehydrocyclising and increases its hydrocyclising capacity.A smaller amount of dialkenes with a five-membered ring is formed on the Pt, Re catalyst than on Pt/Al2O3 and the (Pt, Re)/Al2O3 catalysts are therefore less coke-saturated and are more stable. The sensitivity of the Pt/Al2O3, (Pt, Re)/Al2O3, (Pt, Ir)Al2O3, (Pt, Ge)Al2O3, and (Pt, Sn)/Al2O3 reforming catalysts to poison- ing by sulfur has been investigated in relation to the model cyclohexane dehydrogenation reaction.172 The permissible sulfur content in the starting material when the reaction was carried out on the above catalyst diminished in the sequence (Pt, Ge)>(Pt, Ir)'Pt'(Pt, Sn)>(Pt, Re).The resistance of the catalyst to sulfur decreased in the sequence (Pt, Ge)>(Pt, Ir)'(Pt, Re)>(Pt, Sn). The (Pt, Ge)Al2O3, bimetallic catalyst thus proved to be the most resistant to sulfur and also permitted the highest sulfur content in the starting material. The influence of the rhenium content on the activity, stability, and the resistance to poisoning by sulfur of the (Pt, Re)/Al2O3 reforming catalyst has also been investigated.173 An increase in the rhenium content in the catalysts subjected to preliminary sulfida- tion suppressed the dehydrocyclisation of n-heptane to toluene but facilitated the conversion of methylcyclopentane into benzene without appreciable ring opening.Another result of the increase in the rhenium content was a gradual diminution of the deactivation of the catalyst and of the accumulation of coke on the surface.However, in the presence of a high rhenium content, the catalyst became more sensitive to poisoning by sulfur. The dehydrocycli- sation of n-hexane was suppressed to a greater extent compared with other hydrocarbons. The different behaviour of the catalysts with high and low rhenium contents has been explained by the synergistic activity of rhenium and sulfur. A comparative study of the noncoke-saturated and partially coke-saturated sulfided (Pt, Re)/Al2O3 reforming catalysts in the isomerisation and dehydrocyclisation of hexane, heptane, and methylcyclopentane showed that sulfur promotes the removal of coke from the metal surface.174 The amount of irreversibly chemisorbed sulfur increases in the series of catalysts Pt/ Al2O3<(Pt, Re)/Al2O3<Re/Al2O3. The ensembles of platinum atoms in the (Pt, Re, S)/Al2O3 bimetallic catalysts are larger and have a less distorted structure than in (Pt, S)/Al2O3. 3.Hydrogenation of hydrocarbon mixtures In the 1970s, increased attention was devoted to the questions of the selection of effective catalysts for the hydrogenation of aromatic hydrocarbons in kerosene fractions.The `Unisar' proc- ess was effected on platinum catalysts.175 The modification of platinum catalysts with rhenium makes it possible to achieve the selective hydrogenation of the most undesirable hydrocarbons present in the middle petroleum fractions, namely bicyclic aro- matic hydrocarbons and polysubstituted alkylbenzenes. An advantage of the bimetallic catalyst over the platinum catalyst is also its inertness to hydrocarbons of other classes � alkanes and isoalkanes, particularly in relation to their hydrocracking.4 The effective hydrogen sulfide-treated (l% Pd, 1% Re)/Al2O3 catalyst has been developed for the two-stage hydrogenation of middle petroleum fractions.176 The optimum conditions Rhenium-containing catalysts in reactions of organic compounds 171(T=250 8C, PH2=20 atm, v=1.0 ± 1.5 h71, circulation of 800 ± 1000 litres of hydrogen per litre of starting material), under which the degree of conversion of aromatic hydrocarbons is *90% and the yield of the target product is *98%, were found.A similar degree of conversion of aromatic hydrocarbons on the platinum/alumina catalyst was not attained until 300 8C and a hydrogen pressure of 40 atm. 4. Reforming The greatest advance in the field of petroleum processing has been the achievement in 1968 of the rheniforming process using bimetallic Pt, Re catalysts on an oxide support, which are more active and stable than the platinum/alumina catalyst.19 The improvement of these catalytic systems is being continued at the present time.The application of a new method for the modifica- tion of aluminium hydroxide made it possible to deposit on the latter ultrasmall amounts of platinum (0.15%) and rhenium (0.3%).177 This catalyst, with the ratio Re : Pt=2 : 1 shows a satisfactory activity as well as a high selectivity, stability, and mechanical strength and is readily regenerated.Among all the known reforming catalysts, it contains the smallest amount of platinum. The productivity of the reforming catalyst can be increased by adding a zeolite of the pentasil type.178 The chlorinated (Pt, Re)/ Al2O3 catalyst mixed with HZSM-5 exhibits an increased activity and stability in the formation of aromatic compounds from n-heptane.A possible reaction mechanism involves the formation of intermediate carbonium and carbene ions. The pressure dependence of the yield of hydrogen and of the octane number (o.n.) of the reformate has been investigated on the (Pt, Re)/Al2O3 catalysts.179 The yield of the processing products and hydrogen increased as the pressure increased from 12 to 25 atm.The octane numbers varied linearly with the concentra- tion of the aromatic hydrocarbons. At a pressure of 12 atm, the hydrodealkylation of C8 and higher aromatic hydrocarbons proceeded with formation of xylenes and higher aromatic com- pounds. The conditions for the regeneration of the coke-saturated (Pt, Re)/Al2O3 reforming catalyst by ozone ± air and O2 ±NO2 mix- tures were found.180, 181 Coke was removed by ozone at low temperatures (since ozone decomposes at high temperatures) and then by oxygen.However, ozone removes coke nonselectively, whereas oxygen removes it selectively. In the first place, it was possible to eliminate coke deposited on metallic centres of the catalyst. A special procedure for the `minimisation of the sulfided support' is used in the regeneration of reforming catalysts con- taining chloride and sulfate ions.182 In the presence of an amount of sulfate to which a sulfur concentration in excess of 0.08% ± 0.1% corresponds, the rate of deactivation as a conse- quence of the formation of coke increases.The intensification of the coke formation process is a result, firstly, of the blocking of the Lewis acid centres of aluminium oxide by sulfate ions and, secondly, of the excessive sulfidation of the metal particles by the hydrogen sulfide formed on reduction of the sulfided catalyst by hydrogen. The Pt, Re bimetallic reforming catalyst of type IIP-IPCL (India), exhibited a high activity, selectivity, stability, and capacity for regeneration in tests on a pilot apparatus designed to generate motor fuel.183 The first cycle of tests was interrupted after 13 experiments owing to the deposition of sulfur. In the second cycle, the catalytic activity was lower while the deactivation was very rapid owing to the sulfurisation of the catalyst in the course of the first regeneration.A special technology, involving the removal of sulfates by hydrogen at 490 ± 510 8C and a pressure of 5 ± 7 atm in the presence of ethylene chloride, was therefore used for the second regeneration.After such regeneration, the catalyst recov- ered its initial activity and stability and retained them in the course of three cycles. The influence of temperature and of oxygen content, steam, and hydrocarbons in the gas phase on the initial characteristics of the CB-6 and CB-8 reforming catalysts (China) with a low platinum and rhenium content has been investigated.184, 185 A deficiency of oxygen in the liquid phase leads to the formation of coke in the partial drying and regeneration stages, which induces a decrease in catalytic activity or complete deactivation. The study of the influence of process parameters on the hydrocracking and isomerisation of petrol fractions on (Pt, Re)/ Al2O3 catalysts (R-62 and R-16G) 186 in a flow system has been investigated at T=505 ± 525 8C and v=2.7 ± 5.4 h71.It was established that the yield of liquid products increases with increase in the space velocity. The R-16G catalyst exhibits a high activity in the formation of gaseous products, i.e. in the hydrocracking reaction.This is associated with the influence of the acid centres of aluminium oxide and the use in this case of a higher pressure (27 atm) than in the process on the R-62 catalyst (12 atm). On the other hand, the R-62 catalyst exhibits a higher activity than R- 16G in the dehydrogenation of naphthenes to aromatic hydro- carbons. The reforming of mixed hydrorefined petroleums has been achieved on an industrial pilot apparatus on the same catalysts [T=490 ± 525 8C, v=2.7 ± 5.4 h71, hydrogen : hydro- carbon starting material=(5 ± 7) : l, PH2=27 atm on the R-16G catalyst and 12 atm on the R-62 catalyst].187, 188 An increase in temperature promotes an increase in the octane number of the processing product and the formation of high-quality petrol.The greater activity of the R-62 catalyst in the dehydrogenation of naphthenes to aromatic hydrocarbons noted above can be explained by the fact that the occurrence of this structure- insensitive reaction is promoted by a lower pressure.The catalyst was not deactivated by coke, since its residence in the reactor was brief (*23 h). The dehydroisomerisation and dehydrocyclisation of alkenes to aromatic hydrocarbons occurred to a lesser extent.An increase in temperature and a decrease in space veloty from 0.8 to 0.37 h71 intensified the deposition of coke. The repeated regeneration of the catalyst led to an increase in the pore volume and in the overall porosity.189 The influence of the chlorine content on the properties of fresh, coke- saturated, and regenerated samples of the (0.3% Pt, 0.3% Re)/Al2O3 reforming catalyst has been investigated.190 The equilibrium chlorine content was attained by treating the catalyst with the vapour of the H2O± HCl mixture in a stream of air or hydrogen and was determined by the H2O: HCl molar ratio and also by the temperature of the treatment.The equilibrium chlorine content in the fresh sample was independent of the nature of the chlorine compound introduced. The amount of chlorine retained by the support, calculated per unit surface area, was the same on the fresh and regenerated specimens.The presence of coke did not alter the amount of chlorine on the surface. (Pt, Re)/Al2O3 catalysts have been tested on a pilot apparatus under the conditions of hydrocracking and isomerisation of n-heptane and also under the conditions of the reforming of the petrol fraction with Tb=77 ± 155 8C.191 Problems arising in the use of chlorinated (Pt, Re)/Al2O3 catalysts under industrial conditions, problems of the recovery of the H2O: HCl balance, problems in the monitoring of sulfur, etc.have been examined.192 (Pt, Re)/Al2O3 catalysts prepared by the joint impregnation method and containing chlorine exhibit a high activity because of the decrease in the deposition of coke on their metallic centres.193 The stronger the interaction of the metals in such a catalyst, the smaller the degree of its deactivation by coke.The presence of fluorine on the Al2O3 surface prevents the formation of the strongly bound hexachloroplatinic acid complex PtOxCly.194 Heating in an inert gas leads to the removal of chlorine and the formation of metallic platinum.Treatment with hydrogen limits the possibility of the formation of a homogeneous Pt ± Re solid solution. An increase in the amount of free rhenium in the catalyst promotes the intensification of its hydrogenolysing and the weakening of its aromatising capacities. 172 MA RyashentsevaThe properties of the CB-6 catalyst (China) reduced by electrolytic hydrogen and hydrogen obtained in the reforming process have been compared.195 Reduction by electrolytic hydro- gen led to an increase in the octane number of the petrol formed as a result of reforming by a factor of 2.2 and to a slight increase in the yield.The catalyst reduced by electrolytic hydrogen also possessed a greater stability.However, reduction of (Pt, Re)/ Al2O3 catalyst by the hydrogen, evolved in the course of the reforming of petroleums, is more economical than the reduction by electrolytic hydrogen.196 Sixteen kinetic models were proposed,197 which make it possible to describe the parameters of petroleum reforming processes in the presence of the (Pt, Sn)/Al2O3 and (Pt, Re)/ Al2O3 catalysts.Analysis of the patent literature of recent years 198 ± 228 shows that the selection of effective regenerable rhenium-containing catalysts for the reforming processes is being continued. Pt, Re, Ir catalysts deposited on Al2O3, SiO2, Al2O3 . SiO2, or a zeolite have been proposed.198 ± 200 Tin, cadmium, germanium,201 ± 205 as well as titanium 205 are used as promoting agents instead of iridium.Effective bimetallic platinum ± rhenium supported cata- lysts, activated by chlorine or fluorine, have been devel- oped.206 ± 211 Low-octane petrol fractions are subjected to reforming (220 ± 260 8C, atmospheric pressure) in the presence of 0.1 mass%± 0.3 mass%of Ni, Re, Os, Rh, Ir, Ru, Co, and/or Fe deposited on an oxide support.212 W, V, Mo, Re, Ni, Co, Cr, Mn, and noble metals (Pt or Pd) can also serve as hydrogenating and dehydrogenating components.213 The introduction of lantha- nide oxides, for example Nd2O3, into an aluminosilicate support containing more than 50% of SiO2 increases the activity of the platinum ± rhenium catalyst in reforming and isomerisation proc- esses.214 The combination of processes makes it possible to increase the octane numbers of the reforming products.For example, the product of the conversion of the starting material on the (Pt, Re)/ Al2O3 catalyst is passed for this purpose over the (Pt, Sn)/Al2O3 catalyst.215, 216 Studies associated with the regeneration of the catalysts,217, 218 an increase in their useful lifetime, the reforming technology, etc.219 ± 228 are being continued.Much attention has been devoted to the preparation and physicochemical methods for the analysis of monometallic Pt/ Al2O3 catalysts 229, 230 and also the commonest bimetallic reform- ing catalysts based on Pt and Re, Pt and Sn, Pt and Ir, and Pt and Ge.229 The interaction of the metals in (Pt, Re)/g-Al2O3 bimetallic catalysts has been investigated by the EXAFS and other spectro- scopic methods.231 The likely usefulness of the employment of various Pt, Re clusters with a definite structure in heterogeneous catalysis has been demonstrated by comparing their properties with those of the usual (Pt, Re)/Al2O3 bimetallic reforming catalysts.232 The properties of the 0.3% Pt/Al2O3 (EUROPT-3) and (0.3% Pt, 0.3% Re)/Al2O3 (EUROPT-4) catalysts have been investi- gated in relation to the structure-sensitive hydrogenolysis reac- tions of alkanes (ethane, propane, n-butane, n-hexane, 2- and 3-methylpentanes, n-octane).233 The rate and selectivity of the hydrogenolysis depend on the conditions in the preliminary treat- ment of the catalyst and the residual coke content on the surface.The bimetallic catalyst is more sensitive to the preliminary treat- ment than Pt/Al2O3, since rhenium-enriched phases or pure rhenium may be formed on its surface, which entails a change in the surface ratio Pt : Re.Under the conditions of vigorous hydro- genolysis of alkenes (ethene, butadiene) at 0 and 127 8C in a flow system, the (Pt, Re)/Al2O3 catalyst is rapidly deactivated, in contrast to Pt/Al2O3. The methods for the preparation of bimetallic reforming catalysts, the conditions in their heat treatment, the role of the support, the impregnation methods, the selection of the initial solutions, the stability of the catalysts, and other problems have been discussed.234 Methods for the extraction of rhenium and platinum from spent reforming catalysts have been exam- ined.235, 236 Polymetallic (Pt, Re, Cd)/Al2O3 catalysts of type K-104 have been tested under the conditions of reforming of petrol frac- tions.237 During the initial period, coke is formed on the metallic centres of the RG-482 catalyst.238 On regeneration, it is removed initially from the metallic and then from the acid centres.239 A new trimetallic reforming catalyst, which makes it possible to increase the yield of C5 hydrocarbons and hydrogen compared with the usual (Pt, Re)/Al2O3 bimetallic catalyst, has been proposed in a patent.240 Its stability is not inferior to that of the standard industrial catalyst.Pt/Al2O3 and (Pt, Re)/Al2O3 mono- and bi-metallic catalysts, prepared by the methods used for the synthesis of industrial reforming catalysts, have been investigated by the EXAFS method.241 ± 243 Under the conditions in the reforming of n-heptane, the formation of Pt7C bonds was observed in both mono- and bi-metallic systems.The deposition of carbon was investigated.242, 243 The Pt7C bond is formed at 460 8C on the monometallic catalyst, whereas on (Pt, Re)/Al2O3 it is formed only at low temperatures, the process being accompanied by an appreciable change in the structure of the metallic particles.Modification of platinum with rhenium increases the stability of the catalyst and prevents the deposition of well structured carbon residues. The results indicate also the presence of a long Re7O bond (2.20 A) in the reduced (Pt, Re)/Al2O3 catalysts, which does not conflict with the idea that a structure formed as a result of the insertion of Re into Al2O3 exists.Such a structure emerges partly onto the surface and is reduced by the carbon ± hydrogen mixture. (Pt, Re)/Al2O3 catalysts have also been investigated by transmission electron microscopy combined with energy disper- sive X-ray analysis.244 ± 246 Rhenium ± platinum alloy is not formed in this catalyst and there is a wide size distribution of the rhenium crystals on the support surface.244 Two types of platinum particles have been observed: three-dimensional metallic particles and small formations containing a few atoms.Some aggregation of the platinum particles in the course of the process has been observed under the conditions of the reforming of n-octane. The interaction of rhenium with Al2O3 and preliminary modification of platinum influence significantly the stability and selectivity of the catalyst in reactions involving cycloalkanes and in aromatisa- tion processes.The distribution of active elements in (Pt, Re)/ Al2O3 catalysts has been examined.245, 246 The TAP method (Temporal Analysis of Products�analysis of reaction products as a function of time) has been used to investigate the conversion paths of C6 hydrocarbons on the Pt/ Mg(Al)O, Pt/KL (K is an ion-exchange zeolite), and Pd/Mg(Al)O catalysts, as well as (0.3% Pt, 0.3% Re)Al2O3 industrial catalysts (sulfided and nonsulfided).247 The reactions were carried out under pulsed conditions at 477 and 510 8C, a pressure of 1 atm, and a H2 flow rate of 0.25 ml min71.The reforming products were analysed mass-spectrometrically.It was found that only benzene is formed from cyclohexane, while hex-l-ene is either dehydrocyclised or is hydrogenated to n-hexane with subsequent dehydrogenation and ring closure. The possible dehydrogenation of hexane to hexadiene with subsequent cyclisation takes place at approximately the same rate as that of the dehydrogenation of cyclohexane to benzene. Under the chosen conditions, the sulfi- dation of the catalyst does not exert an appreciable influence on the course of the reaction.Under industrial conditions at high pressures, the formation of benzene from alkanes on the (Pt, Re)/Al2O3 catalyst proceeds via a two-stage mechanism.248 The application of the oxygen ± hydrogen titration method 249 made it possible to determine the degree of dispersion of platinum with a reproducibility of 3% and of rhenium with a reproduci- bility of 5%.Previously, the reproducibility was 5% for platinum and 10% for rhenium.4 Rhenium-containing catalysts in reactions of organic compounds 173IR spectroscopic study of the adsorption of NO and CO molecules showed that a Pt ± Re alloy or metallic clusters are not formed on the surfaces of reduced (Pt, Re)/Al2O3 catalysts with a low concentration of the metal (0.22% of Pt and 0.43% of Re).250 The TPR andXANES methods have been used to estimate the influence of the content of the metal and of the Re : Pt ratio on the susceptibility of rhenium in (Pt, Re)/Al2O3 catalysts to reduc- tion.251 It was found that the final oxidation state of metallic rhenium depends on both these parameters.The catalysts were investigated with laboratory bench and pilot apparatus. The degree of reduction of rhenium determines the catalytic properties of bimetallic Pt ± Re systems. With increase in the Re : Pt ratio, the lifetime of the catalyst increases and this trend is maintained so long as rhenium continues to be reduced. A second rhenium phase, the appearance of which increases the reduction temper- ature, arises when the Re : Pt ratio exceeds 2 : 1.In the presence of a controlled sulfur content in the starting material, the catalyst with the ratio Re : Pt=2 : 1 works twice as long as the catalyst with the ratio Re : Pt=1 : 1. VI. Conclusion The behaviour of rhenium-containing catalysts in a series of organic reactions is distinguished by specificity compared with the behaviour of other transition metals.The possibility of the modification, activation, and reduction of the concentration of rhenium in the Re2O7/g-Al2O3 catalysts used for the metathesis of unsaturated compounds and functional alkenes has been demon- strated in recent years Unsaturated organic compounds which are difficult to obtain, including chlorine- and oxygen-containing ones, may be synthesised by reactions involving higher alkenes.The use of rhenium-containing catalysts permits metathesis or joint metathesis under milder conditions than on other catalytic systems. Rhenocene hydride, rhenium pentacarbonyl, rhenium oxides with the perovskite structure, and rhenium heptasulfide are effective catalysts of the hydrogenation of a series of organic compounds and condensed nitrogen-containing aromatic ones.Supported rhenium catalysts exhibit a higher activity than the known industrial oxide catalysts in the hydrogenation reactions of oxygen-containing compounds (carboxylic acids, aldehydes, syn- thetic aliphatic acid esters, etc.). The studies on rhenium-containing catalysts, especially bi- and poly-metallic ones, in which rhenium is used in combination with noble and Group VIII transition metals for hydrogenation, dehydrogenation, isomerisation, disproportionation, etc. reac- tions are being continued: the methods for the preparation, activation, regeneration, modification, and analysis of the cata- lysts are being improved and the mechanism of their action is being investigated.The range of physicochemical research meth- ods is being constantly expanded. However, many questions concerning the unique role of rhenium, for example in bimetallic platinum ± rhenium supported catalysts, remain unelucidated or controversial. Rhenium-containing catalysts are widely used in two indus- trial processes�metathesis and reforming. Nowadays more than 30% of the total number of reforming catalysts employed throughout the world consist of Pt, Re catalysts.236 The most promising fields of application of rhenium and its compounds as catalysts still comprise diverse organic reactions as well as reactions with participation of CO, CO2, O2, H2O, and chlorine-containing compounds.The catalytic properties of rhenium have been discovered not long ago, so the possibilities for its employment in catalysis are still far from being exhausted.References 1. W Noddack, I Tacke, O Berg Naturwissenschaften 13 567 (1925) 2. I Druce Rhenium. Dvi-Manganese, the Element of Atom Number 75 (Cambridge: The University Press, 1948) 3. M A Ryashentseva, Kh M Minachev Usp. Khim. 38 2050 (1969) [Russ. Chem. Rev. 38 944 (1969)] 4. M A Ryashentseva, Kh M Minachev Renii i Ego Soedineniya v Geterogennom Katalize (Rhenium and Its Compounds in Hetero- geneous Catalysis) (Moscow: Nauka, 1983) 5.H Tropsch, R Kassler Chem. Ber. 63 2149 (1930) 6. H Tropsch, R Kassler Zpr. U st. Ve d. Vyzk. Uhle  2 13 (1932) 7. S B Anisimov, V M Krasheninnikova, M S Platonov Zh. Obshch. Khim. 5 1059 (1935) a 8. H S Broadbent, L H Slaugh, N L Jarvis J.Am. Chem. Soc. 76 1519 (1954) 9. H S Broadbent, G C Campbell, W J Bartly, J H Johnson J. Org. Chem. 24 1847 (1959) 10. A A Balandin, E I Karpeiskaya, A A Tolstopyatova Dokl. Akad. Nauk SSSR 122 227 (1958) b 11. A A Balandin, E I Karpeiskaya, A A Tolstopyatova Izv. Akad. Nauk SSSR, Otd. Khim. Nauk 1365 (1959) 12. M A Ryashentseva, Kh M Minachev, in VIII Mendeleevskii S'ezd po Obshchei i Prikladnoi Khimii.Sektsiya Khimii i Khimicheskoi Tekh- nologii Topliv (Tez. Dokl.) [The VIIIth Mendeleev Congress on General and Applied Chemistry. Section of the Chemistry and Chemical Technology of Fuels (Abstracts of Reports)]) (Moscow: Izd. Akad. Nauk SSSR, 1959) p. 93 13. H Prinzler, H Klotzsche Wiss. Z. Tech. Hochsch. Chem. `Carl Schor- lemmer' Leuna-Mersebg. 329 (1960/1961) 14. M A Ryashentseva, Kh M Minachev, Yu A Afanas'eva Neftekhimiya 2 37 (1962) 15. M A Ryashentseva, Kh M Minachev, Yu A Afanas'eva Neftekhimiya 3 55 (1963) 16. R L Banks,G C Bailey Ind. Eng. Chem., Prod. Res. Dev. 3 170 (1964) 17. T G Khaimova, E A Shepeleva, A A Mkhitarova Neftepererab. Neftekhim. 28 (1989) 18. US P. 3 415 737; Ref. Zh. Khim. 2 P 151P (1970) 19.D H Stormont Oil. Gas J. 67 63 (1969) 20. G N Maslyanskii, B B Zharkov, A P Fedorov, in Vazhneishie Protsessy Neftepererabotki Uglevodorodnogo Syr'ya (The Most Important Processes in the Processing of Hydrocarbon Raw Materials) (Moscow, 1979) p. 10 2 B Zharkov, in Neftekhimiya (Petrochemistry) (Leningrad: Nauka, 1985) p. 12 22. T M Millensifer, in Rhenium and Rhenium Alloys (Ed. B D Bryskin) (Orlando: The Minerals Metals and Materials Society, 1997) p. 43 23.K J Ivin Oleén Metathesis (London: Academic Press, 1983) 24. J C Mol J. Mol. Catal. 15 32 (1982) 25. J C Mol CHEMTECH 13 250 (1983) 26. C Boelhouwer, J C Mol J. Am. Oil. Chem. Soc. 61 425 (1984) 27. J C Mol, J A Moulijn, in Catalysis: Science and Technology Vol. 8, Ch. 2 (Berlin: Spinger, 1977) p. 69 28. J C Mol, J A Moulijn Adv. Catal. 24 131 (1975) 29. J C Mol, in Oleén Metathesis and Polymerisation Catalysts (Dordrecht, Netherlands: Kluwer Academic, 1990) p. 247 30. F Kapteijn, PhD Thesis, University of Amsterdam, The Netherlands, 1983 31. A Ellison, A K Coverdell, P F Dearing Appl. Catal. 8 109 (1983) 32. A Olsthoorn, C Boelhouwer J. Catal. 44 207 (1976) 33. A Andreini, Xu Xiaoding, J C Mol Appl.Catal. 27 31 (1986) 34. E Verkuijlen, F Kapteijn, J C Mol, C Boelhouwer J. Chem. Soc., Chem. Commun. 198 (1977) 35. Xu Xiaoding, P Imhoff, G C N Van den Aardweg, J C Mol J. Chem. Soc., Chem. Commun. 273 (1985) 36. Xu Xiaoding, C Boelhouwer, J I Benecke, D Vonk, J C Mol J. Chem. Soc., Faraday Trans. 1 82 1945 (1986) 37. Xu Xiaoding, D Vonk, J C Mol Thermochim.Acta 105 135 (1986) 38. R Spronk, J A R Van Veen, J C Mol J. Catal. 144 472 (1993) 39. Xu Xiaoding, J C Mol, C Boelhouwer J. Chem. Soc., Faraday Trans. 1 82 2707 (1986) 174 MA Ryashentseva40. J A Moulijn, J C Mol J. Mol. Catal. 46 1 (1988) 41. R Spronk, J C Mol Appl. Catal. 76 143 (1991) 42. R Spronk, J C Mol Appl. Catal. 70 295 (1991) 43. R Spronk, F H M Dekker, J C Mol Appl.Catal. A, Gen. 83 213 (1992) 44. M Sibeijn, J A R Van Veen, A Blick, J A Moulijn J. Catal. 145 416 (1994) 45. A V Anisimov, A A Grishkyan, A B Ryabov, A V Tarakanova Neftekhimiya 31 46 (1991) 46. F D Mango J. Am. Chem. Soc. 99 6117 (1977) 47. E S Shpiro, V I Avaev, G N Antoshin, M A Ryashentseva, Kh M Minachev J. Catal. 55 402 (1978) 48. L G Duquette, R C Cieslinski, C W Jung, P E Carron J.Catal. 90 362 (1984) 49. A V Anisimov, D E Shelemin, V N Opekunov Vestn. Mosk. Univ., Ser. 2, Khim. 36 57 (1995) c 50. E I Bogolepova, S B Verbovetskaya, I V Vygodskaya, G A Kliger, S M Loktev Neftekhimiya 26 185 (1986) 51. E I Bogolepova, I V Vygodskaya, A V Bulanova, G A Kliger, S M Loktev Neftekhimiya 27 106 (1987) 52. E I Bogolepova, I V Vygodskaya, G A Kliger, S M Loktev Neftekhimiya 31 305 (1991) 53.E I Bogolepova, I V Vygodskaya, A V Bulanova, G A Kliger, S M Loktev Neftekhimiya 29 234 (1989) 54. E I Bogolepova, I V Vygodskaya, G A Kliger, S M Loktev Neftekhimiya 30 507 (1990) 55. E I Bogolepova, I V Vygodskaya, G A Kliger, S M Loktev Neftekhimiya 32 504 (1992) 56. E I Bogolepova, I V Vygodskaya, G A Kliger, S M Loktev Neftekhimiya 35 104 (1995) 57.E I Bogolepova, I V Vygodskaya, T S Vinogradova, G A Kliger, S M Loktev Neftekhimiya 35 113 (1995) 58. USSR P. 1 132 968; Byull. Izobret. (1) 33 (1985) 59. M A Ryashentseva, Kh M Minachev, B M Bulychev, V M Ishchenko Izv. Akad. Nauk SSSR, Ser. Khim. 2707 (1988) d 60. H S Broadbent,W J Bartley J. Org. Chem. 28 2345 (1963) 61. USSR P. 1 132 969; Byull. Izobret. (1) 33 (1985) 62.M A Ryashentseva, Kh M Minachev, V N Khandozhko, N E Kolobova Izv. Akad. Nauk SSSR, Ser. Khim. 2859 (1990) d 63. M Ryashentseva, in Rhenium and Rhenium Alloys (Ed. B D Bryskin) (Orlando: The Minerals Metals and Materials Society, 1997) p. 179 64. M A Ryashentseva, Kh M Minachev, V V Fomichev, V A Bardin Izv. Akad. Nauk SSSR, Ser. Khim. 1236 (1986) d 65. S Kemmler-Sack, J Jooss Z.Anorg. Allg. Chem. 439 232 (1978) 66. M Herrmann, S Kemmler-Sack Z. Anorg. Allg. Chem. 470 113 (1980) 67. M A Ryashentseva, A A Dulov, L A Abramova, O P Tkachenko, V V Fomichev, A E Vetrov J. Catal. 125 1 (1990) 68. USSR P. 293 805; Byull. Izobret. (6) 61 (1971) 69. E A Mistryukov, E L Ilkova,M A Ryashentseva Tetrahedron Lett. 20 1691 (1971) 70. M A Ryashentseva, E A Mistryukov, E L Il'kova Izv.Akad. Nauk SSSR, Ser. Khim. 1865 (1972) d 71. M A Ryashentseva, Kh M Minachev, N A Tsibisova Izv. Akad. Nauk SSSR, Ser. Khim. 1583 (1973) d 72. M A Ryashentseva, N S Prostakov Khim. Geterotsikl. Soedin. 1443 (1982) e 73. R Alarkon Khorkhe, S A Soldatova, A T Soldatenkov, M A Ryashentseva, N S Prostakov Izv. Akad. Nauk SSSR, Ser. Khim. 1413 (1991) d 74.O B Zaporozhets, M A Ryashentseva, V M Polosin, R V Poponova Izv. Akad. Nauk SSSR, Ser. Khim. 1267 (1993) d 75. A T Soldatenkov, S A Soldatova, Kh A R Alarkon, Zh A Mamyrbekova, L I Kryvenko, Zh Ntaganda, M A Ryashentseva Khim. Geterotsikl. Soedin. 377 (1994) e 76. V G Pleshakov, K D Ambacheu, M A Ryashentseva, N D Sergeeva,M V Vener, L A Murugova, O V Zvolinskii, N S Prostakov Izv.Akad. Nauk, Ser. Khim. 1098 (1994) d 77. N M Kolyadina, A T Soldatenkov,M A Ryashentseva, N S Prostakov Izv. Akad. Nauk, Ser. Khim. 180 (1996) d 78. Kh M Minachev, V I Avaev, R V Dmitriev,M A Ryashentseva Izv. Akad. Nauk SSSR, Ser. Khim. 1456 (1984) 79. H Kubicka, J Okal. Catal. Lett. 25 (1 ± 2) 157 (1994) 80. H Kubicka, J Okal. React. Kinet. Catal. Lett. 34 433 (1987) 81. A Benedetti, G Cocco, S Enco, F Pinna Kinet.Catal. Lett. 13 291 (1980) 82. H Kubicka, J Okal React. Kinet. Catal. Lett. 19 419 (1982) 83. G A Del Angel, B Coq, G Ferrat, F Figueras Surf. Sci. 156 943 (1985) 84. Q A Martin, J A Dalmon J. Catal. 75 233 (1982) 85. P Marecat, E Paraiso, J M Dumas, J Barbier Appl. Catal. 74 261 (1991) 86. E H Van Broekhoven, J W F M Schoonhoven, V Ponec Surf.Sci. 156 899 (1985) 87. Kh M Minachev, V I Avaev,M A Ryashentseva Izv. Akad. Nauk SSSR, Ser. Khim. 306 (1986) d 88. V I Avaev,M A Ryashentseva, Kh M Minachev Izv. Akad. Nauk SSSR, Ser. Khim. 22 (1988) d 89. BRD P. 3 217 429; Chem. Abstr. 98 88 817 (1983) 90. V I Avaev, A V Zaitsev, V Yu Borovkov,M A Ryashentseva, V B Kazanskii, Kh M Minachev Kinet. Katal. 31 1179 (1990) f 91.M A Ryashentseva, V I Avaev, Kh M Minachev, Zh A Evdokimova, V N Pavlychev Neftekhimiya 28 324 (1988) 92. A P Tyupaev, E A Timofeeva, G V Isagulyants Izv. Akad. Nauk SSSR, Ser. Khim. 2460 (1980) d 93. M A Ryashentseva, Kh M Minachev, Yu A Afanas'eva Neftekhimiya 2 41 (1962) 94. Jpn. P. 04 305 539; Chem. Abstr. 118 83 280 (1993) 95. Jpn. P. 04 305 540; Chem. Abstr. 118 83 281 (1993) 96.BRD P. 4 200 790; Chem. Abstr. 120 61 641 (1994) 97. US P. 5 136 113; Chem. Abstr. 117 170 778 (1992) 98. Jpn. P. 07 196 565; Chem. Abstr. 124 55 422 (1996) 99. M A Ryashentseva, Kh M Minachev,M P Yunusov, A T Serodzhev Neftekhimiya 22 364 (1982) 100. M A Ryashentseva, Kh M Minachev, I K Anikeev Neftekhimiya 24 49 (1984) 101. Jpn. P. 04 099 753; Chem. Abstr. 117 111 140 (1992) 102.Jpn. P. 06 092 885; Chem. Abstr. 121 157 276 (1994) 103. Jpn. P. 07 118 187; Chem. Abstr. 123 227 623 (1995) 104. Jpn. P. 06 145 159; Chem. Abstr. 121 133 944 (1994) 105. Jpn. P. 07 053 539; Chem. Abstr. 122 290 703 (1995) 106. Jpn. P. 06 306 069; Chem. Abstr. 122 105 644 (1995) 107. BRD. P. 4 422 046; Chem. Abstr. 124 201 996 (1996) 108. Jpn. P. 07 082 187; Chem. Abstr. 123 82 816 (1995) 109. Jpn. P. 07 082 189; Chem. Abstr. 123 82 818 (1995) 110. Jpn. P. 07 082 188; Chem. Abstr. 123 82 817 (1995) 111. Jpn. P. 07082190; Chem. Abstr. 123 82 819 (1995) 112. WO PCT 9 202 298; Chem. Abstr. 117 29 190 (1992) 113. Jpn. P. 06 157 490; Chem. Abstr. 121 157 510 (1994) 114. BRD P. 4 339 269; Chem. Abstr. 123 32 943 (1995) 115. BRD P. 4 325 753; Chem. Abstr. 122 264 899 (1995) 116.Jpn. P. 04 082 851; Chem. Abstr. 117 69 457 (1992) 117. Jpn. P. 04 082 852; Chem. Abstr. 117 69458 (1992) 118. T S Tang,K Y Cheah, F Mizukami, S Niwa,M Toba, Y M Choo J. Am. Oil Chem. Soc. 70 601 (1993); Chem. Abstr. 119 75 015 (1993) 119. BRD P. 4 230 565; Chem. Abstr. 120 322 744 (1994) 120. M Rusek Stud. Surf. Sci. Catal. (Heterog. Catal. Fine Chem. 2) 59 359 (1991); Chem.Abstr. 116 43385 (1992) 121. Jpn. P. 0 508 5991; Chem. Abstr. 119 50 085 (1993) 122. US P. 5 410 086; Chem. Abstr. 123 32 667 (1995) 123. V M Belousov, T A Pal'chevskaya, L V Bogutskaya Ukr. Khim. Zh. 57 924 (1991); Chem. Abstr. 116 201 849 (1992) 124. T A Pal'chevskaya, L V Bogutskaya, V M Belousov Ukr. Khim. Zh. 57 1285 (1991); Chem. Abstr. 117 150 405 (1992) 125.V M Belousov, T A Pal'chevskaya, L V Bogutskaya, V A Zazhigalov Kinet. Katal. 34 269 (1993) f 126. S M Augustine, M S Nacheff, C M Tsang, J B Butt, W M H Sachtler, in Catalysis 1987 (Proceedings of the 10th National American Meeting of Catal. Society) (Amsterdam: Elsevier, 1987) p. 1190 127. M J Dees, J den Harton, V Pones Appl. Catal. 72 343 (1991) 128. A P Barkova, D B Furman, O V Bragin Izv.Akad. Nauk SSSR, Ser. Khim. 474 (1992) d 129. A P Barkova, O V Bragin, D B Furman Izv. Akad. Nauk SSSR, Ser. Khim. 484 (1993) d 130. V Yu Borovkov, A P Barkova, G S Dorokhina, A V Zaitsev, D B Furman, O V Bragin, V B Kazanskii Izv. Akad. Nauk SSSR, Ser. Khim. 664 (1993) d Rhenium-containing catalysts in reactions of organic compounds 175131. A P Barkova, D B Furman, V B Kazanskii Kinet.Katal. 37 630 (1996) f 132. M A Ryashentseva Izv. Akad. Nauk SSSR, Ser. Khim. 2119 (1996) d 133. Z Xu, Z Qian, H Hattori Bull. Chem. Soc. Jpn. 64 3432 (1991) Chem. Abstr. 116 105 422 (1992) 134. T Matsuzaki, K Takeuchi, T Hanaoka, H Arakawa, Y Sugi Sekiyu Sakkaishi 37 (2) 179 (1994); Chem. Abstr. 120 201529 (1994) 135. T Matsuzaki, K Takeuchi, T Hanaoka, H Arakawa, Y Sugi Appl.Catal., A 105 159 (1993) 136. T Matsuzaki,K Takeuchi, T Hanaoka,H Arakawa, Y Sugi Trans. Mater. Res. Soc. Jpn. 18A (Ecomaterials) 417 (1994); Chem. Abstr. 123 206 483 (1995) 137. P M Torniainen, X Chu, L D Schmidt J. Catal. 146 1 (1994) 138. J B Claridge,M L H Green, S C Tsang Catal. Today 21 453 (1994) 139. S R Mirzabekova, A Kh Mamedov, O V Krylov Kinet. Katal. 37 276 (1996) f 140. A Kh Mamedov, S R Mirzabekova, O V Krylov Kinet. Katal. 36 635 (1995) f 141. R Qukaci, J G Goodwin Jr, G Marcelin, A Singleton, in Proceedings of the 11th Annual Internatial Pittsburgh Coal Confer- ence, 1994 Vol. 1, p. 62; Chem. Abstr. 123 318 293 (1995) 142. S Vada, A Hoff, E Aadnanes, D Schanke, A Holmen Top. Catal. 2 155 (1995); Chem. Abstr. 124 12 067 (1996) 143.L E Skaare Rygh, I Gausemel, O H Ellested, P Klaeboe, C J Nielsen, E Rytter J. Mol. Struct. 394 325 (1995); Chem. Abstr. 122 325 129 (1995) 144. M A Ryashentseva, V P Rozhdestvenskii, A B Polyanskii, S E Molina Neftekhimiya 21 33 (1981) 145. V P Rozhdestvenskii,M A Ryashentseva, A B Polyanskii, S E Molina Neftekhimiya 24 179 (1984) 146. M A Ryashentseva, Kh M Minachev, V P Rozhdestvenskii, S E Molina, A B Polyanskii Neftekhimiya 28 328 (1988) 147.I P Belomestnykh, G V Shakhnovich, N N Rozhdestvenskaya, M A Ryashentseva, G V Isagulyants Izv. Akad. Nauk SSSR, Ser. Khim. 985 (1987) d 148. Kh M Minachev, O M Nefedov,M A Ryashentseva, V V Kharlamov, A M Shkitov, in Primenenie Tseolitov v Katalize (Tez. Dokl. III Vsesoyuznoi Konferentsii) [The Use of Zeolites in Catalysis (Abstracts of Reports at the Third All-Union Conference)] (Moscow: Nauka, 1985) p. 35 149. Kh M Minachev, V V Kharlamov,M A Ryashentseva Izv. Akad Nauk SSSR, Ser. Khim. 2076 (1988) d 150. S B Ziemecki, G A Jones, J B Michel J. Catal. 99 207 (1986) 151. L P Prasel, U Panchareon, J Tscheikuna Kenkyu Hokoku-Asahi Garasu Zaidan 61 313 (1992); Chem. Abstr. 119 142 465 (1993) 152.S C Bond,M R Gelsthorpe Kem. Kozl. 73 (1) 51 (1991); Chem. Abstr. 117 30 075 (1992) 153. R Zhen-Kui, T Long-Xiang J. Nat. Gas. Chem. 4 384 (1995); Chem. Abstr. 123 317 451 (1995) 154. J Wang, Q Zhang, X Vang,G Xu Shiyou Xuebao, Shiyou Jiagong 9 (2) 26 (1993); Chem. Abstr. 120 274 865 (1994) 155. Y Xu, F Sun Shiyou Xuehan, Shiyou Jiagong 10 (1) 8 (1994); Chem. Abstr. 121 137 238 (1994) 156.C L Pieck, P Marecot, C A Querini, J M Parera, J Barbier Appl. Catal., A 133 281 (1995) 157. H Du, R Wu, L Fang, H Wang, L Lin Appl. Catal. 78 1 (1992) 158. F Haike,M Vasile Prog. Catal. 1 1 (1992); Chem. Abstr. 119 273816 (1993) 159. USSR P. 1 691 410; Buyll. Izobret. (42) 130 (1991); Chem. Abstr. 117 237 018 (1992) 160. X E Verykios Commun. Eur. Communities (Rep.) EUR. 13 843 (1992); Chem. Abstr. 116 155 208 (1992) 161. M Koussathana, N Vamvouke, X Verykios Int. J. Energy Res. 18 243 (1994); Chem. Abstr. 121 183 190 (1994) 162. G Del Angel, J Bertin,A Perez, R Gomez React. Kinet. Catal. Lett. 48 259 (1992) 163. G Munuers, P Malet, A Caballero Stud. Surf. Sci. Catal. (New Frontiers Catal. A) 75 781 (1993); Chem. Abstr. 119 184 274 (1993) 164.C Prieto, V Briois, P Parent, F Villain, P Lagerde, H Dexpert, B Fourman, A Michalowicz, M Verdauger AIR Conf. Proc. (Syn- chrotron Radiat. Dyn. Phenom.) 258 621 (1992); Chem. Abstr. 118 88 361 (1993) 165. X Luo, J He, Z Sun, Z Shen Fenzi Cuihua 6 434 (1992); Chem. Abstr. 118 84 110 (1993) 166. C Q Michel, W E Bambrick, R H Ebel Fuel Process. Technol. 33 (1 ± 2) 159 (1993); Chem.Abstr. 119 229 627 (1993) 167. F H Ribeiro, A L Bonivardi, C Kim, G A Somorjai J. Catal. 150 186 (1994) 168. F H Ribeiro, A L Bonivardi, G A Somorjai Catal. Lett. 27 (1 ± 2) 1 (1994) 169. C L Pieck, E L Jablonski, J M Parera, R Frety, F L Lefebvre Ind. Eng. Chem. Res. 31 (4) 1017 (1992); Chem. Abstr. 116 155 110 (1992) 170. C Kim, G A Somorjai Chem. Ind. (Dekker) 53 511 (1994) 171.C A Querine, S C Fung J. Catal. 141 389 (1993) 172. A Borgna, T F Garetto, A Mozon, C R Apestegufa J. Catal. 146 69 (1994) 173. J Shao, J Wang, C Wu, J Ling Shiyou Xuebao, Shiyou Jiagong 7 (4) 39 (1991); Chem. Abstr. 117 174 674 (1992) 174. L Poenitsch,M Wilde, P Tetenyi,M Dobrovolsky, Z Paal Appl. Catal., A 86 115 (1992); Chem. Abstr. 117 236 223 (1992) 175. R C Hansford, D A Gandio, T V Inwood, V T Mavity Oil Gas J. 67 134 (1969) 176. A D Martynyuk, Candidate Thesis in Chemical Sciences, VNIIPK Neftekhim, Kiev, 1985 177. F Sun,Y Xu Shiyou Xuebao, Shiyou Jiagong 11 (1) 12 (1995); Chem. Abstr. 123 87 739 (1995) 178. J N Beltramini, R Fang Stud. Surf. Sci. Catal. (Catal. Petroleum Reéning Petrochem. Ind. 1995) 100 465 (1996); Chem. Abstr. 124 236 626 (1996) 179.K Moljord, H G Hellenes, A Hoff, J Tanem, K Grande, A Holmen Ind. Eng. Chem. Res. 35 99 (1996); Chem. Abstr. 124 12 013 (1996) 180. C L Pieck, E L Jablonski, J M Parera Stud. Surf. Sci. Catal. (New Frontiers Catal., Pt. C) 75 2535 (1993); Chem. Abstr. 119 120 804 (I993) 181. C L Pieck, E L Jablonski, J M Parera Stud. Surf. Sci. Catal. (Catal. Deactivation 1994) 88 289 (1994); Chem. Abstr. 123 117 763 (1995) 182. T F Garetto, A Borgna, C R Apesteguia, J C Lavalley Ind. Eng. Chem. Res. 31 1283 (1992); Chem. Abstr. 116 217 649 (1992) 183. V K Kapoor, J R Rai, Y K Kuchhal, R K Agarwal, R P Mehrota, K R Murthy, N Sharma, N George Stud. Surf. Sci. Catal. (Catal. Deactivation 1994) 88 359 (1994); Chem. Abstr. 123 148 460 (1995) 184. Y Liu,G Pan, J Yang Shiyou Lianzhi (9) 1 (1992); Chem. Abstr. 119 31 175 (1993) 185. Y Liu, X Zeng Shiyou Lianzhi 24 (8) 8 (1993); Chem. Abstr. 120 327 062 (1994) 186. K Sertic-Bionda, Z Vrabanovic, V Rukavina, S Zrncevic Chem. Biochem. Eng. Q. 6 (3) 133 (I992); Chem. Abstr. 118 9064 (1993) 187. K Sertic-Bionda, Z Vrbanovic, S Zrncevic, V Rukavina Erdoel, Kohle, Erdgas, Petrochem. 15 (4) 167 (1992); Chem. Abstr. 117 30 079 (1992) 188. K Sertic-Bionda, Z Vrbanovic, V Rukavina, S Zrncevic Kem. Ind. 41 (8) 297 (1992); Chem. Abstr. 118 41 956 (1993) 189. K Sertic-Bionda, Z Vrbanovic, V Rukavina Erdoel, Kohle, Erdgas, Petrochem. 17 (6) 234 (1994); Chem. Abstr. 121 112 946 (1994) 190. O A Scelza, G T Baronetti, S R de Migael, P Silber, A A Castro J. Chem. Technol. Biotechnol. 58 135 (1993); Chem. Abstr. 119 253322 (1993) 191. D Zhang, J Di, C Du, Z Sun Shiyou Xuebae, Shiyou Jiagong 9 (1) 34 (1993); Chem. Abstr. 120 274 872 (1994) 192. J Zhang Shiyou Lianzhi Yu Huagong 25 (4) 26 (1994); Chem. Abstr. 121 60 956 (1994) 193. C L Pieck, P Marecot, J M Parera, J Barbier Appl. Catal., A 126 153 (1995); Chem. Abstr. 123 13 246 (1995) 194. S Engels, E Herhold, H Mayr, H W Meiners, H Lausch Chem. Tech. (Leipzig) 44 (3) 100 (1992); Chem. Abstr. 116 217 667 (1992) 195. C Cai Shiyou Lianzhi 3 19 (1992); Chem. Abstr. 117 236 867 (1992) 196. W Lu,W Wan Shiyou Lianzhi Yu Huagong 26 (6) 68 (1995); Chem. Abstr. 123 117 791 (1995) 197. H Weng, H Jiang, Z Chen Huagang Xuebao Chin. Ed. 45 531 (1994); Chem. Abstr. 122 59 753 (1995) 198. Eur. P. 448 366; Chem. Abstr. 116 24 504 (1992) 199. USSR P. 1 664 791; Buyll. Izobret. (27) 100 (1991); Chem. Abstr. 116 237 821 (1992) 200. USSR P. 1 740 362; Buyl. Izobret. (22) 76 (1992); Chem. Abstr. 121 136 589 (1994) 176 MA Ryashentseva201. USSR P. 1 734 817; Buyll. Izobret. (19) 33 (1992); Chem. Abstr. 120 222 191 (1994) 202. US P. 5 221 463; Chem. Abstr. 119 227 881 (1993) 203. US P. 5 342 506; Chem. Abstr. 121 208 932 (1994) 204. Eur P. 606 007; Chem. Abstr. 121 113 094 (1994) 205. US P. 5 346 611; Chem. Abstr. 121 283 399 (1994) 206. Fr. P. 2 659 569; Chem. Abstr. 116 44 020 (1992) 207. US P. 5 198 404; Chem. Abstr. 119 52 658 (1993) 208. Chin. P. 1 073 197; Chem. Abstr. 119 229 886 (1993) 209. DDR P. 299 230; Chem. Abstr. 118 42 117 (1993) 210. Czech. P. 279 448; Chem. Abstr. 124 12 182 (1996) 211. US P. 5 106 800; Chem. Abstr. 117 52 222 (1992) 212. Russ. P. 1 796 660; Buyll. Izobret. (7) 83 (1993); Chem. Abstr. 120 249 081 (1994) 213. US P. 5 296 428; Chem. Abstr. 121 38 979 (1994) 214. US P. 5 208 200; Chem. Abstr. 119 76 129 (1993) 215. US P. 5 196 110; Chem. Abstr. 119 52 657 (1992) 216. US P. 5 211 838; Chem. Abstr. 119 99 689 (1993) 217. US P. 5 391 292; Chem. Abstr. 122 269 847 (1995) 218. WO PCT 9 516 009; Chem. Abstr. 123 148 676 (1995) 219. Czech. P. 275 455; Chem. Abstr. 120 81 212 (1994) 220. WO PCT 9 419 428; Chem. Abstr. 121 234 391 (1994) 221. US P. 5 316 992; Chem. Abstr. 121 61 282 (1994) 222. Russ. P. 2 024 581; Buyll. Izobret. (23) 84 (1994); Chem. Abstr. 123 88 027 (1995) 223. Russ. P. 2 019 557; Buyll. Izobret. (17) 88 (1994); Chem. Abstr. 123 61 094 (1995) 224. Russ. P. 2 032 465; Buyll. Izobret. (10) 117 (1995); Chem. Abstr. 124 33512 (1996) 225. Jpn. P. 07 163 884; Chem. Abstr. 123 174 780 (1995) 226. US P. 5 254 518; Chem. Abstr. 120 81 217 (1994) 227. US P. 5 268 344; Chem. Abstr. 120 111 413 (1994) 228. Russ. P. 2 027 506; Chem. Abstr. 123 343 437 (1995) 229. J P Boitiaux, J M Deves, B Didillon, C R Marcilly Chem. Ind. (Dekker) 61 79 (1995); Chem. Abstr. 122 217 847 (1995) 230. B H Davis, G J Antos Chem. Ind. (Dekker) 61 113 (1995); Chem. Abstr. 122 217 848 (1995) 231. J-R Chang Shiyou Jikan 30 (1) 23 (1994); Chem. Abstr. 121 60 817 (1994) 232. J Xiao, R J Puddephatt Coord. Chem. Rev. 143 457 (1997); Chem. Abstr. 123 323 202 (1995) 233. G C Bond J. Mol. Catal. 81 99 (1993) 234. J Zhang Shiyou Lianzhi 24 (4) 40 (1993); Chem. Abstr. 121 13 590 (1994) 235. J P Rosso,M I Guindy Chem. Ind. (Dekker) 61 395 (1995); Chem. Abstr. 122 193 026 (1995) 236. M L El Guindy, in Rhenium and Rhenium Alloys (Ed. B D Bryskin) (Orlando: The Minerals Metals and Materials Society, 1997) p. 90 237. G M Sen'kov, N S Kozlov, in Promyshlennye Katalizatory Riforminga (Industrial Reforming Catalysts) (Minsk: Nauka i Tekhnika, 1986) p. 226 238. G M Senkov, A A Artyukh, V M Yakubenko, L I Titova, A M Nikitina,M F Gorbatsevich Vesti Akad. Navuk Belarusi, Ser. Khim. Navuk 3 89 (1995); Chem. Abstr. 124 293 759 (1996) 239. G M Senkov, A A Artyukh, A M Nikitina, M F Gorbatsevich, L I Titova, L P Filanchuk Vesti Acad. Navuk Belarusi, Ser. Khim. Navuk 4 32 (1995); Chem. Abstr. 124 293 761 (1996) 240. R W Morse, P W Vance, V J Novak, J P Franck, J C Plumail Fuel Reformulation 3 (3) 31, 33, 36, 38 (1995); Chem. Abstr. 124 206 622 (1996) 241. A Caballero, F Villain, H Dexpert, F Lepeltier, B Didillon, J Lynch Catal. Lett. 20 1 (1993) 242. A Caballero, F Villain, H Dexpert, F Lepeltier, J Lynch J. Chem. Soc., Faraday Trans. 89 159 (1993); Chem. Abstr. 118 133 014 (1993) 243. A Caballero, F Villain, H Dexpert, F Lepeltier, J Lynch Jpn. J. Appl. Phys. Part 1 32 439 (1993); Chem. Abstr. 119 206 698 (1993) 244. Z Huang, J R Fryer, C Park, D Stirling, G Webb J. Catal. 148 478 (1994) 245. Z Huang, J R Fryer, C Park, D Stirling, G Webb Inst. Phys. Conf. Ser. 138 469 (1993); Chem. Abstr. 123 18 819 (1995) 246. K V Rao, G C Pandey, K R Murthy Indian J. Chem. A, Inorg., Bio-Inorg. Phys. Theor. Anal. 34 746 (1995); Chem. Abstr. 123 174 517 (1995) 247. D S Lafyatis, G F Froment, F Gilbert, A Pasau-Claerbout, G Eric J. Catal. 147 522 (1994) 248. A J Silvestry, P A Naro, R L Smith J. Catal. 14 386 (1969) 249. S Jiang,M Guo, J Gong Hunan Shifan Daxue Ziran Kexue Xuebao 17 (4) 53 (1994); Chem. Abstr. 122 197 948 (1995) 250. Y Hu, L Zheng Wuli Huaxue Xuebao 11 636 (1995); Chem. Abstr. 123 323 212 (1995) 251. C G Michel, W E Bambrick, R H Ebel, G Larsen, G L Haller J. Catal. 154 222 (1995) a�Russ. J. Gen. Chem. (Engl. Transl.) b�Dokl. Chem. Technol., Dokl. Chem. (Engl. Transl.) c�Moscow Univ. Bull. (Engl. Transl.) d�Russ. Chem. Bull. (Engl. Transl.) e�Chem. Heterocycl. Compd. (Engl. Transl.) f�Kinet. Catal. (Engl. Transl.) Rhenium-containing catalysts in reactions of organic c
ISSN:0036-021X
出版商:RSC
年代:1998
数据来源: RSC
|
|
首页
