摘要:

J. MATER. CHEM., 1991, 1(3), 473-474 MATERIALS CHEMISTRY COMMUNICATIONS Crystallization of Sparingly Soluble Salts on Functionalized Polymers Evangelos Dalas Department of Chemistry, University of Patras, GR-26110, Patras, Greece The introduction of -P(O)(OH),, -P(O)(OH),/-F, -C(O)CH,, -C(O)H and -S(O),OH functional groups on copoly(styrene/butadiene) via epoxidation makes the polymer substrates capable of hydroxyapatite, calcite or a-CdS nucleation and further crystal growth. Keywords: Copolymer; Crystal growth The deposition of sparingly soluble salts on polymers is of paramount importance, not only for fundamental research concerning biomineralization' but also for practical appli- cations, such as design and development of (a)new materials suitable for electronic applications,2 as well as materials suitable for prosthetic applications in bone and teeth;3 (b) new composite materials and materials for phosphate removal from wastewater;, (c) new materials suitable for pollutant removal from wastewater,2 as well as scale-prevention agents for use in detergents and power plants' (calcium carbonate formation takes place on the polymer surface instead of the involved metallic parts).Polymers containing functional groups have been found to nucleate calcium carbonate,' hydroxyapatite (HAP),, iron phosphate4 and cadmium sulphide.2 Results obtained by using a number of polymeric substrates'-' were explained by the assumption that the nucleation of a crystalline salt on a polymer is preceded by the formation of surface ion pairs.We now report for the first time the functionalization of the polymer substrate copoly(styrene/butadiene) via epoxidation and opening of the epoxide group with the acids H3P04, H,PO,/HF, CH3C02H and HC02H, leading to the develop- ment of polymeric substrates not only with good mechanical properties but also capable of inducing inorganic salt nucle- ation and subsequent crystal growth. The physical properties of the copolymers were varied from q=-90 "C, stress at break =0.21 MPa, elongation at break= 124%, for the bare copolymer, to <= -30 "C, stress at break =30.07 MPa, elong- ation at break =817% for 57 mol% epoxide rings per mole of butadiene, indicative of the many mechanical applications.Epoxidation was carried out with the in situ formation of performic acid in toluene solution (5% m/m solids) using an excess (1 10%) of the epoxidizing agent, an equimolar mixture of formic acid and hydrogen peroxide. After the addition of H202 at O'C, the temperature was allowed to rise and was controlled at 20 "Cfor the duration of the epoxidation reac- tion. Other details on the procedure have been described be- fore.6 Epoxidized polymers were characterized using H NMR spectroscopy, CI3 NMR spectroscopy, FTIR spectroscopy and volumetric analysis. The absence of H NMR absorptions at 3.2-3.3 and 3.8 ppm indicates the absence of a diol grouping and a furan ring, respectively. Similarly, no IR absorptions were detected for the above groups, correspondingly at 3430 and 1067 cm-'.In this work more weight was given to NMR analysis since at higher degrees of conversion neighbouring oxirane groups may vitiate chemical analysis results through side reactions, leading to higher-member rings. The epoxide rings were opened by the addition of the acid in a 174-dioxane solution, and the acid residues were titrated with ammonium hydroxide ~olution.~ The functionalized copolymers were pre- cipitated in methanol, treated in a blender, suspended in dis- tilled water and dried at 25 "C for 48 h under vacuum. The functionalized copolymers can be obtained as flexible material as well as semicrystalline powder depending on the degree of functionalization. The powders were suspended in 0.1 mol dm-, calcium nitrate or cadmium nitrate solutions for 24 h under continuous stirring.They were then washed in 1 dm3 of distilled water. Analysis of the washings showed no calcium or cadmium desorption. The degree of copolymer functionalization and the polymer properties are summarized in Table 1. The experiments were done in metastable supersaturated solutions at concentrations appropriate for ensuring stability for long time periods by constant supersaturation.8 All experi- ments were done at 25 "C in a 0.250 dm3 Pyrex glass double- walled vessel thermostatted at 25 0.1 "C by circulating water. More details on this procedure have been described in the literat~re.~.~*'**The driving force for the crystal growth of the various sparingly soluble salts [HAP, Ca,(PO,),OH; calcites CaCO,; and a-CdS] is defined by the equation where (IP), is the activity product at the experimental con- ditions and K;,,is the activity product of the polymorph at eq~ilibrium;~i2, is the saturation ratio of polymorph X, consisting of v ion^.^,^,' The activities of the ionic species were calculated by successive approximations for the ionic strength from the equilibria in solution, mass balances and electroneutrality condition^.^*^*'.^ The experimental con-ditions are detailed in Table 2.The subsequent rates of crystallization were found to increase with supersaturation. Doubling or tripling the amounts of functionalized copolymer introduced in the super- saturated solutions had no effect on the initial rates normalized per unit area of the substrate.It should be noted that the rates we have in the kinetics analysis of our experiments were obtained from the slopes of the curves of titrant addition (reflecting the amount of solid precipitating) at time zero. This is justified by the fact that the amount precipitated continu- ously increased, thus changing the total surface area. Also, changes in the stirring rate had no obvious effect on the rates of crystallization. These facts suggest that the overgrowth of sparingly soluble salts mentioned above is induced by the organic matrix by heterogeneous nucleation." During the course of reaction, samples were withdrawn so as to keep the total volume approximately constant, filtered through a mem- J.MATER. CHEM., 1991, VOL. 1 sample PP SB PPF PAC PFo PSn SP SB SPF SAC SFo PSn Table 1 Functionalized polymers and their characteristics mol% functional Mn!g mol -mol% epoxide groups groups per mol polymer (source) (Mw/Mn) per mole butadiene bu tadienec SSAd/m2 g-' diblock" (Phillips) 189.000 (1.92) 56.4 31 -PO(OH),( 3 5)/ -F(4) 28 -COCH3(38) -COH(39) 25 27 diblockb (Shell) 79.000 (1.24) 25 -S(O),OH(37) -PO(OH),(2 1) 40 35 -PO(OH),( 19)/-F(2) 33 -COCH3(20) 29 -COH(20) 30 -S(O),OH( 19) 48 All block copolymers contained 30% m/m styrene. " Experimental product with ca. 95% purity; commercial product with a reported purity of ca. 80%; determined by titrati~n;~ dspecific surface area.Table 2 Crystallization of sparingly soluble salts on functionalized copolymers polymer substrate precipitating phase" AG/kJ mol-I R/mol min-' rn-, PP HAP(ASTM,9-432) -3.5 8.73 x 10-9 PPF HAP -3.5 9.23 x SP HAP -3.5 1.18 x SPF HAP -3.5 1.77 x PSn calcite (ASTM,5-0586) -3.1 9.38 x lo-' PAC calcite -3.1 1.46 x PFo calcite -3.1 1.04 x 10- SSn calcite -3.1 1.16 x SAC calcite -3.1 2.39 x 10-5 SFo calcite -3.1 2.31 x10-5 Psn u-Cds(ASTM,6-314) -6.9 5.1 x10-7 SSn U-Cds -6.9 6.9 x10-7 " The phases precipitated were characterized by X-ray diffraction analysis according to the ASTM file card no. specified in each case. brane filter (0.2 pm, Gelman, Cellulose Nitrate), and the filtrates were analysed.The solid phases on the filters were analysed by powder X-ray diffraction (Philips 1300/00), infra- red spectroscopy (Perkin-Elmer, IR spectrophotometer 297), specific surface area (multiple point B.E.T., Perkin-Elmer Model 2 12D sorptometer), and thermogravimetric analysis (TG) (Du Pont 910). It has been demonstrated that the introduction of func-tional groups on the surface of otherwise inactive copolymers (styrene/butadiene) converted then into effective nucleators of sparingly soluble salts. P(OXOH), and P(O)(OH),/ -F( 10% mol F)/(mol of functional groups) groups converted them into selective nucleators of HAP, thus, along with the mechanical properties, providing a basis for their consider- ation as prosthetic materials.The introduction of the -F groups increased the nucleation rate as expected from previous studies." -C(0)CH3 and -C(O)H groups induce the crys- tallization of the calcium carbonate polymorph calcite, whereas the -S03H groups at the styrene/butadiene surface induce the crystallization of calcite, in contrast to the previous results that -S03H groups on polystyrene crystallize calcium carbonate m~nohydrate.~ This evidence suggests that the crystalline polymorph forming is controllable both from the functional group and the polymer substrate. It should be noted that the growth of calcium carbonate on the sulphonated and carboxylated polymers is selective for these functionalized polymers. Thus, it was found that phos- phorylated polymers, when introduced in calcium carbonate solutions, supersaturated with respect to calcite, aragonite, vaterite and calcium carbonate monohydrate, were not able to induce the formation of any of these phases.The sulphonated copolymers also induce the crystallization of cadmium sulphide, a-CdS, when introduced into cadmium sulphide supersaturated solutions. Finally, a consideration of the polarity of the P=O, C=O or S=O bond, in which the negative charge is shifted towards the oxygen atom, suggests that the formation of HAP, calcite or CdS may be initiated through the interaction of Ca2+ or Cd2+ ions with the negative end of the P=O, C=O or S=O bond. References I L. Addadi, J. Moradian, E. Shay, N. G. Maroudas and S. Weiner, Proc. Natl. Acad. Sci. USA, 1987,84, 2732. 2 E. Dalas, J. Kallitsis, S. Sakkopoulos, E. Vitoratos and P. G. Koutsoukos, J. Colloid Interface Sci., 1991, in the press. 3 E. Dalas, J. Kallitsis and P. G. Koutsoukos, Colloids SurJ, 1991, in the press. 4 E. Dalas, J. Colloid Interface Sci., 1991, in the press. 5 E. Dalas, J. Kallitsis and P. G. Koutsoukos, J. Crystal Growth, 1988, 89, 287. 6 A. G. Margaritis, J. K. Kallitsis and N. K. Kalfoglou, Polymer, 1989, 30,2253. 7 J. E. Davey and M. J. R. Loadman, Br. Polym. J., 1984, 16, 134. 8 P. Koutsoukos, Z. Amjad, M. B. Tomson and G. H. Nancollas, J. Am. Chem. Soc., 1980, 102, 1553. 9 R. M. Smith and A. C. Martell, Critical Stability Constants, Plenum, New York, 1976, vol. 3. 10 J. W. Mullin, Crystallization, CRC Press, Boca Raton, FL, 2nd edn., 1972. 11 P. G. Koutsoukos and G. H. Nancollas, J. Crystal Growth, 1981, 53, 10. Communication 1/00605C; Received 8th February, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100473

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(3), 475-476 Tetrathiafulvalene-FePS, Layered Intercalation Compound: A New Type of Organic-Inorganic Metal Leticia Lomas, Pascal Lacroix, Jean Paul Audiere and Rene Clement" Laboratoire de Chimie lnorganique, C. N.R.S. U.R.A. 420, Universite Paris Sud, 91405 Orsay Cedex, France Layered FePS, preintercalated with tetraethylammonium cations reacts with (TTF),(BF4), in acetonitrile to yield Fe, -pS3(TTF)2x(xx0.18).This intercalation compound has a metallic character, in contrast to pure FePS, which is a semiconductor. Keywords: Layered material; Intercalation; Molecular metal The MPS, layered materials, where M is a transition metal in the 2+ oxidation state, give rise to unusual intercalation chemistry based on the ability of the MPS3 slabs to lose a variable amount of M' intralayer cations.'?' This provides + an opportunity to build up air-stable composites having original properties with respect to the parent compounds, such as the ferromagnetic intercalates with high Curie tem- peratures recently described., Intercalation of tetrathiafulva- lene (TTF) monocations by ion exchange has already been achieved in two MPS, phases (M=Mn, Cd): in contrast to the redox processes involved in the previously developed intercalation chemistry of TTF into FeOCl, silicates and V205.5-9This communication shows that insertion of TTF' cations into FePS3 leads to an intercalation compound which exhibits electrical properties drastically different from those of the pure host material.Pure FePS, was synthesized by reaction of the elements at 730 OC.l0 Intercalation was carried out in two steps. A sample of the tetraethylammonium intercalate Fe, -xPS3(Et,N),x(solv), (x xO.14) was obtained by treating FePS, (2 days at 50°C) with a large excess of an aqueous solution containing Et,NCl (ca. 1 mol drn-,) and EDTA (ca. 0.02 mol drn-,) at ca. pH 10 fixed by a Na2C03/NaHC03 buffer. Insertion of TTF monocations was then achieved by treating the above intercalate (ca.200 mg) with a solution of ca. 200 mg of (TTF)3(BF,)211 in dry acetonitrile (ca.20 cm3) for 2 days at 50°C. The black powder obtained was then filtered off, washed with acetonitrile and dried. All operations were performed under an argon atmosphere, but the final material appears to be stable in air.Complete intercalation and ion exchange were ascertained by elemental analyses, X-ray powder diffraction and IR spec- troscopy. The X-ray powder diffraction pattern shows that the material obtained is highly crystalline as it exhibits sharp hkl reflections which can be readily indexed in a monoclinic unit cell (Table 1) closely related to that of pristine FePS,. Parameters a and b along the plane of the layers remain essentially unchanged. The interlamellar distance increases by ca. 5.65 A as a result of intercalation, which strongly suggests that the TTF species stand 'edge on' with respect to the FePS, slabs, with the C=C binary axis parallel to the layers, as in the FeOCl intercalates.' Elemental analyses of the intercalate (noted 1 hereafter) were performed (in wt.%: Fe, 18.5; P, 12.5; S, 56.9; C, 11.1; H, 0.75).These data lead to a formula Fe0.82PS3(TTF)0.38 very close to Fe, -xPS3(TTF),, (x z0.18). The TTF content is consistent with an expected value 0.39 calculated on the basis of close-packed TTF species" perpendicular to the layers. Infrared spectra of 1 (KBr pellets) showed evidence for the presence of TTF species (sharp bands at 1480, 830, 740 cm-l, broad strong band CQ. 1300 cm-'). The v(PS3) Table 1 Indexing of Feo.82PS3(TTF),.,8, at room temperature. Cell dimensions, a =5.919 A, b = 10.348 A, c = 12.642 A,j?= 107.45' spacing/A obs. calc. hkl intensity 12.02 12.06 001 m 6.030 6.030 002 W 3.015 3.015 004 W 2.943 2.943 130 S 2.762 2.762 131 S 2.496 2.496 132 m 1.725 1.725 060 m 1.706 1.707 061 m 1.657 1.658 062 W 1.488 1.489 261 m 1.459 1.456 401 m 1.415 1.412 400 m asymmetric stretching band, which occurs at 570 cm-' in pure FePS,, is split into three components at 650, 580 and 602 cm-'.This band is usually split into only two components in the MPS, intercalates, the splitting reflecting the presence of intralamellar metal vacancies.' The d.c. electrical conductivity, CT, of 1 along the plane of the layers was measured in the range 110-370 K, using classical four-probe techniques. Large quasi-monocrystalline (giving sharp X-ray reflections) platelets of the intercalate were prepared following the procedure described above, but increased the reaction duration by a factor of ca.3. Gold electrodes were deposited on the platelets by evaporation under vacuum. Results are plotted in Fig. 1. The conductivity of 1 is quite large (ox3R-' cm-' at 25 "C) and does not 100 200 300 TIK Fig. 1 Temperature dependence of the d.c. electrical conductivity of 1 476 appear to be thermally activated. Indeed, CT increases as the temperature is lowered, a behaviour which indicates a metallic character for 1. Such a metallic character sharply contrasts with the semi- conducting properties of pure FePS3 (and more generally of all MPS3 material^).'^ It also contrasts with the semiconduct- ing properties of the previously studied MPS,-TTF interca-lates where M =Mn, Cd.' The different behaviour of the present intercalate might therefore be related to the ability of the intralayer Fe" cations to be partially oxidized by the interlayer TTF+ species.Such charge transfer would result in mixed valency on both the host and the guest sublattices. This view is supported by preliminary results of a 56Fe Mossbauer study which provides evidence for the presence in 1 of some Fe"' ~ati0ns.I~ References 1 R. Clement, J. Chem. SOC., Chem. Commun., 1980,647. 2 R. Clement, 0.Garnier and J. Jegoudez, lnorg. Chem, 1986, 25, 1404. J. MATER. CHEM., 1991,VOL. 1 3 R. Clement, L. Lomas and J. P. Audiere, Chem. Muter., 1990, 2, 641. 4 P.Lacroix, J. P. Audiere and R.Clement, J. Chem. SOC.,Chem. Commun., 1989, 537. 5 M. R.Antonio and B. A. Averill, J. Chem. SOC., Chem. Commun., 1981,382. 6 H.Van Damme, F. Obrecht and M. Letellier, Nouv. J. Chem., 1984, 8, 681. 7 S. M. Kauzlarich, B. K. Teo and B. A. Averill, lnorg. Chem., 1986,25, 1209. 8 S. M.Kauzlarich, J. L. Stanton, J. Faber Jr. and B. A. Averill, J. Am. Chem. SOC.,1986, 108, 7946. 9 J. F. Bringley, J. M. Fabre and B. A. Averill, J. Am. Chem. SOC., 1990,112,4577. 10 W. Klingen, R. Ott and H.Hahn, 2. Anorg. Allg. Chem., 1973, 396,271. I1 F. Wudl, J. Am. Chem. SOC.,1975,W,1962. 12 W. F.Cooper, N. C. Kenny, J. W. Edmonds, A. Napel, F. Wudl and P. Coppens, J. Chem. SOC., Chem. Commun., 1971, 889. 13 R. Brec, Solid State lonics, 1986, 22, 3, and references therein. 14 R. Clement, W. R. Dunham and A. H. Francis, to be published. Communication 1 /00866H;Received 22nd February, 199I

ISSN:0959-9428    

DOI:10.1039/JM9910100475

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(3), 477-478 Madelung Energy and Hole Location in YBa,Cu,O, Sheela K. Ramasesha"and K. Thomas Jacob* "Materials Science Division, National Aeronautical Laboratorx Bangalore 560 0 17, India Department of Metallurgx Indian Institute of Science, Bangalore 560 0 12, India The Madelung energy of YBa,Cu,O, has been computed for different locations of the hole in the structure. The lowest-energy configuration corresponds to partial localization of the hole on 0(1)and O(11) sites. Keywords: Coulomb interaction; Madelung potential; Valence fluctuation; Mixed valence; Hole location Although there has been significant effort, both theoretical and experimental, to understand the location of holes in YB~,CU,O,-~, very little attention has been focussed on the nature of charge carriers in YBa2Cu408 (124).Madelung energy computations provide a simple method for exploring the sites for hole localisation in complex structures. Earlier calculations on the YBa,Cu307 (1 23) compound' indicated that the most probable sites for hole localisation are Cu(1) and O(4) following the nomenclature of Siegriet et aL2 In this communication we explore the minimum-energy locations for holes in the 124 compound. In order to maintain charge neutrality in the 124 compound, a hole has to be localised on copper, oxygen or copper- oxygen ligand. The structure of the 124 compcund is similar to that of the 123 compound except that there is an extra Cu-0 chain in 124. The crystal structure and site descrip- tions are given in Fig.1. Madelung potentials are computed using the Ewald method. Potential around an ion i due to all other ions in the crystal is given by where A is the unit cell volume, G is the reciprocal lattice vector, qi is the charge of the ion around which potential is calculated, qr is the charge of other ions in the crystal, rl is the distance between the ith ion and other ions, S(G) is the structure factor given by S(G)=&,exp(-iG*r,) (2)t and F (x)is the error function of the form The value of the constant q is chosen such that the summations in eqn.( 1) converge rapidly. The computer pro- gram used in this study was checked initially on simple compounds such as NaCl and CsCl. The program was further verified by computing the Madelung potential of YBa2Cu3O7 with holes localized on chain Cu sites.The value of -335.9843 eV obtained compares well with -335.996 eV reported by Tsay et aL3 Atomic positions and cell parameters of the unit cell are 63 Ba @Y 0 cu 00 Fig. 1 The unit cell of YBa,Cu,O, with site description of all the atoms taken from Marsh et aL4 Since the number of formula units per unit cell is two for this compound, potentials have to be calculated around 30 atoms. Symmetry considerations reduce the number of unequal positions to 16. Then by proper multiplicity factors, the Madelung energy, EMad,of the unit cell is calculated. There is one hole per formula unit of YBa2Cu408. The Madelung energy is calculated by localising the hole at different sites in the unit cell.Calculations for hole localisation on the four copper sites [Cu(l), Cu(ll), Cu(2), Cu(21)] and eight oxygen sites [O(l), 0(1 l), 0(2), 0(21), 0(3), 0(31), 0(4), O(41)J are carried out. Since in these high T, superconductors, there is a possibility of hybridi~ation,~-' partial localisation of the hole on several combinations of oxygen sites, copper sites and mixed copper-oxygen sites is considered. A few cases in which hole is localized on three of four sites are also J. MATER. CHEM., 1991, VOL. 1 Table 1 Madelung energy (EMa& and energy of formation (E,) of YBa,Cu,O, from isolated ions Y3+, Ba2+, Cu2+ and 0,-in the gas phase for different locations of holes EMad Ef EMad Ef EMad Ef hole location /eV /eV hole location /eV lev hole location ~~ -737.52 -663.86 -739.29 -665.63 -690.19 -662.1 1 -741.85 -668.19 -658.43 -675.93 -691.39 -663.3 1 -717.60 -643.94 -649.09 -666.59 -691.23 -663.15 -644.84 -662.34 -645.03 -662.53 -690.2 1 -662.13 -652.23 -669.83 -650.78 -668.28 -690.24 -662.16 -643.82 -661.32 -653.08 -670.58 -663.44 -635.36 -617.28 -634.78 -691.93 -663.85 -684.48 -656.39 -645.43 -662.93 -693.26 -665.1 8 -662.55 -634.47 -620.1 1 -637.61 -690.67 -662.59 -681.15 -653.07 -648.17 -665.67 -696.46 -668.38 -690.18 -662.10 -653.15 -670.65 -691.0 -662.92 -687.85 -659.77 atomic sites on which the holes are localized are identified.considered.In such situations, one hole per unit cell is localized on the copper sites and another hole on the oxygen sites. The total Madelung potential, EMvlad,of the unit cell with holes localised on different sites is tabulated in Table 1. The Madelung potential gives the energy associated with building an ionic lattice from constituent ions in the gas phase. In order to determine which configuration has the lowest energy, it is important to refer the energies to a common reference +frame. For convenience one may consider ions of Y ,Ba2+ , Cu2+, 02-in the gas phase at infinite separation as the starting point for the synthesis of different configurations. In cases in which the hole is localised on oxygen sites, two 02-ions have to be converted per unit cell to 0-ions in the gas phase before assembling the ions to form a unit cell in the lattice. When the hole is localised on the copper sites, two Cu2+ ions per unit cell have to be converted to Cu3+ ions before building the lattice.Where the hole is partially localised on both oxygen and copper sites, one 02-ion has to be converted to 0-and one Cu2+ to Cu3+. Total energy of formation, Ef, of different configurations, calculated using a value of 36.83 eV for the third ionisation energy of Cu and -8.75 eV for O2-+O-+e in the gas phase, are also summar- ised in Table 1. Since the core-repulsion energy is a constant for a given composition, it does not influence the relative stability of the different configurations for YBa2Cu408.The lowest-energy configuration according to the calcu- lation is that for which the hole is partially localised on 0(1) and O(1 1) sites. It is interesting that complete hole localisation on either O(1) and O(1 1) sites gives a high energy of formation. Partial localisation on 0(1) and O(l1) sites is equivalent to oxygen valence fluctuation along two planes containing these ions. Both these planes contain a barium atom. The onset of superconductivity probably arises from phase synchronization of valence fluctuations along these planes. The second lowest-energy configuration corresponds to holes localisation on O(41). Partial localisation on 0(1)and O(41) sites also gives comparable values. However, these configurations have energies of formation that are more than 5 eV higher and are therefore unlikely to represent the hole distribution at low temperatures. All other possible locations for holes give rise to higher energies of formation.The YBa2Cu408 has a structure similar to that of YBa2Cu307 except for the extra Cu-0 chain which causes the unit cell to be doubled. In YBa2Cu307, from Madelung potential calculations, it was found that the holes were local- ised on the Cu(1) and O(4) sites. The holes being localised on the O(1) and O(11) sites with the introduction of another Cu-0 chain is rather surprising. Other evidence for the importance of the 0(1) site in the superconductivity of YBa2Cu408 is provided by high-pressure studies. Kaldis et aL8 have shown that the apical oxygen [O(l)] is dis- placed towards the CuOz plane under pressure.Eenige et al.' have found that T, increases dramatically with pressure in YBa2Cu408. In contrast, the Cu(1)-O(1) distance and T, in YBa2Cu30, are not significantly affected by pressure."-" It thus appears that the sites for hole localisation are differ- ent in YBa2Cu4o8 and YBa2Cu307. The authors are grateful to Mrs. R. Sarojini for assistance in the preparation of the manuscript. References 1 S. K. Ramasesha and K. T. Jacob, Muter. Lett., 1990, 10, 239. 2 T. Siegriet, S. Sunshine, D. W. Murphy, R. J. Cava and S. M. Zahurak, Phys. Rev. B, 1987, 35, 7137. 3 S. F. Tsay, S. Y. Wang, L. Horng and T. J. W. Yang, Phys. Rev. B, 1989, 40, 9408. 4 P. Marsh, R. M. Fleming, M. L. Mandich, A. M. Desantolo, J. Kwo, M. Hong and L. J. Martinez-Miranda, Nature (London), 1988, 334, 141. 5 L. F. Mattheiss, Phys. Rev. Lett., 1987, 58, 1028. 6 W. Weber and L. F. Mattheiss, Phys. Rev. B, 1988, 37, 599. 7 C. M. Varma, S. Schmitt-Rink and E. Abrahams, Solid State Commun., 1987, 62, 681. 8 E. Kaldis, P. Fischer, A. W. Hewat, E. A. Hewat, J. Karpinski and S. Rusiecki, Physica C, 1989, 159, 668. 9 E. N. Van Eenige, R. Griessen, R. J. Wijngaarden, J. Karpinski, E. Kaldis, S. Rusiecki and E. Jilek, Physica C, 1990, 168, 482. 10 J. D. Jorgensen, S. Pei, P. Lightfoot, D. G. Hinks, B. W. Veal, B. Dabrowski, A. P. Paulikas, R. Kleb and I. D. Brown, Physicu C, 1990, 171, 93. 11 A. Driessen, R. Griessen, N. Koeman, E. Salomons, R. Brouwer, D. G. de Groot, K. Heeck, H. Hemmes and J. Rector, Phys. Rev. B, 1987,36, 5602. Communication 1/00240F; Received 17th January, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100477

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991,1(3), 479-480 Novel Co-operative Magnetic Properties of Decamethylmanganocenium 2,3-Dichloro-5,6- dicyanobenzoquinoneide, 3[Mn(C,Me,),]:+[DDQ]-- Joel S. Miller,*" R. Scott McLean,aCarlos Vazquez,' Gordon T. Yee,"nb K. S. Narayadand Arthur J. Epstein*b'Central Research and Development (Contribution No. 5810), Du Pont, Experimental Station E328, Wilmington, DE 19880-0328, USA Department of Physics and The Department of Chemistry, The Ohio State University, Columbus, OH 432 10-1106, USA The electron-transfer salt 3[Mn(C,Me,),]"[DDQ]~-l isomorphous to orthorhombic [Fe(C,Me,),],+[DDQ].-, has been prepared. It exhibits a complex field-dependent magnetic phase diagram at low temperatures with evidence for ferromagnetic coupling as well as a low moment state below 4 K for zero-field cooled samples.Keywords: Decamethylmanganocenium 2,3-dichlor~5,6-dicyanobenzoquinoneide;Electron-transfer salt; Ferro- magnetic coupling Co-operative (bulk) magnetic behaviours have been observed for the [FeCpt].' [TCNE].-(Cp*=pentamethylcyclopen-tadienide; TCNE =tetracyanoethylene) and [FeCpt].' [TCNQ]. -(TCNQ=7,7,8,8-tetracyano-p-quinodimethane) electron-transfer salts.' The former has been characterized by powder neutron diffraction and single-crystal measurements to exhibit a spontaneous magnetization (ferromagnetic ground state) with a Curie temperature, T,, of 4.8K,whereas the latter is metamagnetic with a Nee1 temperature, TN,of 2.55K. The solution of a simple (one spin site) mean-field model shows that Tc is proportional to J and S(S+ 1) where J is the exchange integral and S is the spin.2 Attempts to enhance Tcby substituting the S=1/2Fe"' cation with the isostructural S= 1 Mn"' cation, i.e.3[MnCp$]:+, in the [TCNE].- salt were unsuccessful owing to decomposition arising from the chemi- cal reactivity of the donor and a~ceptor.~ Recently, the expected trend has been realized with the report that the [TCNQ].- salt of 3[MnCp;]'+ is ferr~magnetic.~ The observed magnetic couplings are consistent with the expectations of the extended-McConnell configurational admixture model.' With the goal of preparing additional molecular-based ferromag- nets, the ferromagnetically coupled [FeCpt]*+ [DDQ].- (DDQ = 2,3-dichloro-5,6-dicyanobenzoquinone) electron-transfer salt was characterized.6 As Tc is proportional to S(S+l),we sought to prepare 3[MnCp;]'+[DDQ]*-, antici-pating that Tc might occur at temperatures accessible in our laboratories.The salt 3[MnCp?]"[DDQ]*-was prepared from 3[Mn(C,Me,)2]'f[PF6]-(ref. 7) and [Et,N]+[DDQ].- [ref. 6(b)] at -20 "C. Elemental analysis (Oneida Research Ser- vices) for C28H30C12MnN202 calc. (obs.): C, 60.88, (60.39); H, 5.47 (5.32);N, 5.07% (5.49%). Infrared spectra (Nujol): v,,, 2205s cm-' (C=N) (cf. 2206s cm-' for [FeCpt].+ [DDQ].-).6 Room temperature Gunier powder diffraction analysis was used to determine the unit-cell lattice parameters (a= 14.48A, b= 17.00A, c= 10.69A, and V=2631.5 A3)which are isomorphous to the Fe"' analogue (a= 14.497A, b=17.027A, c =10.616A, and V= 2620 A3).60Thus, although crystals suitable for single-crystal X-ray analysis are not available, powder diffraction data supports the assump-tion that [Mn(C5MeS)2].'[DDQ]'-possesses the [Fe(C,Me,),].+ [DDQ]*- structure comprising parallel in- +and out-of-registry -D.A--D.+A. chains.60 The 2-300 K Faraday balance8 magnetic susceptibility of [Mn(CSMe5)2]"[DDQ]*-can be fit by the Curie-Weiss expression, xM =C/(T-0). The effective moment, peff [~(8xT)'/~],and 8 values for five independently prepared samples are 4.22,4.25,4.30,4.13,and 4.13pB and +25.5,25.8, 27.1, 28.8, and 31.9K, and average 4.21 pB and 27.8K, respectively. The moment is greater than expected from a randomly oriented sample based on (g) (i.e.3.1 1 pB for (g) = 2.207),but less than expected for a sample oriented with the C5 axis parallel to the magnetic field (i.e. 4.71 pB for gll= 3.33).Thus, owing to the orientational variability of polycrys- talline samples, the observed effective moments are consistent with S = 1/2and S=1 ions per formula unit. The Curie-Weiss 8 value of +26.8K suggests significant ferromagnetic interac- tions. Hysteretic magnetic-field-dependent behaviour was observed below ca. 7K. The 150-2000 G magnetic field dependence of the magnetization for a zero-field cooled sample previously aligned by 19.5kG magnetic field is presented for increasing and decreasing magnetic fields in Fig. 1. Above ca. 3.8K the magnetization exceeds the expectation calculated from the Brillouin function for fully aligned S=1 and S = 1 /2 spins.Thus, the data imply a complex magnetic phase diagram at low temperature. Assuming complete alignment of the crystals with the magnetic field parallel to the C5 molecular axis, the expected saturation magnetization, M,, of 24 200 emuG mol- is realized. This is consistent with ferro- magnetic coupling. At ca. 4 K the magnetization abruptly drops by more than an order of magnitude depending on the applied field to a value lower than calculated from the Brillouin function, Fig. 1. At high temperature there is a field- dependent cross-over from a low to a high magnetization state. This is suggestive of the presence of perhaps both a spin-Peierls and metamagnetic transitions.However, since spin-Peierls transitions occur only in antiferromagnetic states, complex magnetic behaviours must be operative for the material. Details of the phase diagram consistent with both the low- and high-field cooling for DDQ as well as the other dihalo-DDQ salts will be reported later. t gll=3.33, g, =1.64 and (g) =2.20 were observed for neutral MnCpf at 4 K in methyltetrahydrofuran. Under similar conditions attempts to determine the EPR of [MnCpt]:+[PF,]-were unsuc-cessful. J. MATER. CHEM., 1991, VOL. 1 -24 000 20 000- 20 000-.-I .--I-0 '16000-16000-'? E ;f' 9 i i.o 12 000 -.o 12 000-4-Y .-2 .-2 CI 4-4al al m m E 8000-' 8000-4000 -4000 -0- 0- 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16 temperature, T/K temperature, T/K Fig.1 Molar magnetization, M, as a function of temperature, T, for a zero-field cooled polycrystalline sample of [MnCpz]:+[DDQ]'- previous aligned in 19.5 kG at 150 (m), 200 (O), 300 (x), 400 (O),500 (A), 750 (O),1000 (A),1500 (0),and 2000 (+) G magnetic fields applied at each temperature value in an (a) increasing and (b) decreasing manner. The magnetization calculated from the Brillouin function for fully aligned S= 1 and S= 1/2 spins at 2000 G (---). (The actual field application sequence was 150, 300, 500, 1000, 2000, 1500, 750,400, and 200 G prior to annealing at 25 K in zero field for 30 min and then applying 200, 400, 750, 1500, 2000, 1000, 500, 300, and 150 G fields) We gratefully acknowledge support from the U.S.Department of Energy Division of Materials Science Grant No. DE-FG02-86ER45271.A000. We appreciate the powder X-ray diffraction analysis kindly provided by C. Foris and G. Hyatt and EPR spectra taken by w-Barney s. Hill, and p. J-Krusic at Du Pont CR&D. References 1 J. S. Miller, A. J. Epstein and W. M. Reiff, Chem. Rev., 1988, 88, 201; J. S. Miller, A. J. Epstein and W. M. Reiff, Acc. Chem. Res., 1988, 21, 114; J. S. Miller and A. J. Epstein and W. M. Reiff, Science 1988, 240, 40. 2 J. H. Van Vleck, The Theory of Electric and Magnetic Suscepti- bilities, Oxford University Press, London, 1932; J. H. Van Vleck, Rev. Mod. Phys., 1945, 17, 7; J. H. Van Vleck, Rev.Mod. Phys., 1953, 25, 220; J. B. Goodenough, Magnetism and the Chemical Bond, John Wiley Interscience, New York, 1963; R. L. Carlin, Magnetochemistry, Springer-Verlag, Berlin, 1986; C. Kittel, Zntro-duction to Solid State Physics, John Wiley, New York, 5th edn., 1976; D. A. Dixon, A. Suna, J. S. Miller and A. J. Epstein, in NATO AR W Molecular Magnetic Materials, ed. 0. Kahn, D. Gatteschi, J. S. Miller and F. Palacio, 1991, XX,171. 3 J. S. Miller and A. J. Epstein. Adv. Chem. Ser. 1990. 226.419. 4 W. E. Broderick, J. A. Thompson, E. P. Day and B. M. Hoffman, Science, 1990, 249, 410. 5 J. S. Miller and A. J. Epstein, J. Am. Chem. SOC., 1987, 109, 3850, 6 (a) E. Gerbert, A. H. Reis, J. S. Miller, H. Rommelmann and A. J. Epstein, J. Am. Chem. SOC., 1982, 104, 4403; (b) J. S. Miller, P. J. Krusic, D. A. Dixon, W. M. Reiff, J. H. Zhang, E. C. Anderson and A. J. Epstein, J. Am. Chem. SOC., 1986, 108, 4459. 7 J. L. Robbins, N. Edelstein, B. Spencer and J. C. Smart, J. Am. Chem. SOC., 1982, 104, 1882. 8 J. S. Miller, D. A. Dixon, J. C. Calabrese, C. Vazquez, P. J. Krusic, M. D. Ward, E. Wasserman and R. L. Harlow, J. Am. Chem. SOC., 1990, 112, 381. Communication 1/01 1521; Received 12th March, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100479

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(3), 481-482 48 1 Photoinduced Reversible Refractive-index Changes in Tailored Siloxane-based Polymers Susan H. Barley, Andrew Gilbert and Geoffrey R. Mitchell* Polymer Science Centre, University of Reading, Whiteknights, Reading RG6 ZAF; UK The design and synthesis of novel polymers for use in optical-fibre space switching devices is described. These materials consist of a low refractive index matrix with a small fraction of photoactive units together with adjuster units to tailor the refractive index to that of silica. These materials show reversible and controlled variation in the refractive index which is induced through selective irradiation at either 366 or 525 nm. Keywords: Photoactive polymer; Optical communication; Hydrosilation ; Refractive index At present, voice, computer and other electronic information is transferred at high speeds and densities over large distances using high-bandwidth optical-fibre systems.One of the factors which governs the more general application of optical trans- mission is the ability to switch and route signals without the need for repeated conversion to and from the electronic domain. It is clear that there are considerable advantages to be gained if the switching processes could be made without such transformations, in other words if the switching were performed optically. One particular possibility associated with optical fibres is the construction of switching devices directly involving the optical fibres, in which the transfer is made by coupling the evanescent wave in one fibre into a second fibre.' A number of methods have been employed in attempts to produce switches based on this process.'-' An intermediate material may be placed between the two cores such that when the refractive index of that material is low no transfer takes place; in effect the intermediate layer acts as the cladding.However, if the refractive index is raised then coupling or switching is achieved. A relatively small change in refractive index is required to activate the switching mechanism. In this contribution we report the design, synthesis and characteristics of novel polymeric materials for use in a system in which the heart of the optical-fibre switch is stimulated using light.The most basic problem of designing a suitable material for such a switch is that the refractive index of the material must more or less match that of the optical-fibre core. For conventional telecommunication optical fibres this is ca. 1.46. Most 'active' materials such as liquid crystals or non-linear optical films have inherently high refractive indices. In the materials described here this problem is circumvented by utilising a material whose matrix has a low refractive index, into which are introduced a small proportion of photoactive groups. These photoactive groups undergo reversible cis-trans isomerisation, and this allows the photoactive units to be optically pumped almost exclusively from the trans to cis states and vice versa.In addition to the change in optical absorption characteristics and hence refractive index, the trans and cis isomers have different molecular shapes. These induced geometric changes to the photoactive groups may invoke variations in the optical properties of the matrix material, for example through the effective bulk density. The materials described here, therefore, consist of a polymer backbone, which will give rise to a low-refractive-index material [in our case poly(dimethylsiloxane)], photoactive units, which in this example are azobenzene derivatives, and an 'adjuster' unit, by which the overall refractive index is tailored to match that of silica, and these are dodecane moieties. Poly(dimethylsi1ox- ane) itself has a refractive index of ca.1.399-1.4035* and a remarkably low glass-transition temperature, two attributes which make it particularly suitable for the base material in these devices. The reversible photoisomerisation of azobenzene units is well establishedg although we have considered the use of alternative photoactive units." The attachment of the photoactive units to the siloxane backbone was performed using the Pt-catalysed hydrosilation reaction."-12 The base polymer poly(methylsi1oxane) was reacted with 4-(allylo~y)azobenzene'~and dodec- I-ene in varying amounts to produce a range of polymers with con- trolled refractive indices and differing levels of azobenzene (Scheme 1). The base polymer poly(methylsi1oxane) (PMS) with Mw4500-5000 was used as supplied from Petrarch.To a solution of PHS (5 g, 0.105 mmol) in toluene (220cm3) 4-(allyloxy)azobenzene and dode-1 -ene were added in the required ratios followed by a freshly prepared solution of H2PtC1, in isopropyl alcohol (0.01 mol dm-3, SiH :Pt ratio of 1 :5 x This mixture was heated under nitrogen at 50-60 "C for 1 h followed by refluxing until no sign of the Si-H absorption peak (2155 cm-') could be seen by infrared spectroscopy. Typical yields for the hydrosilation were 50%. In order to determine the photoinduced refractive-index changes, thin films of each polymer were cast from dichloro- methane solution directly onto the prism face of an Abbe I I CH3-Si-0 Si-0 Si-CH3 ICH3 + + CH2=CH--(CH2)g-CH, Scheme 1 482 Refractometer.These thin films were irradiated using a wave- length band of light of 16 nm width centred at 366nm to pump from the trans to the cis states and at 525 nm to reverse the transition. The light source was a Xe/Hg broad-band arc lamp (200 W) equipped with an elliptical mirror (Photon Technology International) illuminating the slit of a grating monochromator (Jobin Yvon H 1OUV) through a water-based infrared filter. The fraction of the cis isomer was determined, after removal of a small portion of the film onto a quartz substrate, using a UV-VIS spectrometer (Perkin-Elmer 330). The method employed a calibration curve, constructed using the spectra recorded for solutions of 4-(allyloxy)azobenzene which had been characterised using high-performance liquid chromatography. l4 Typically, over the composition range the errors associated with the determination of the cis fraction were 15% and those with refractive-index measurements were 3 x 104.The temperature coefficient of a polymer with q =0.05 was 3 x K-'. The thermally driven cis+trans conversion was sufficiently slow (time to 50% conversion ca.20 h at 16 "C) to facilitate these measurements after illumination. Fig. 1 shows the variation induced in the refractive index through selective irradiation in a siloxane polymer with q= 0.05 and its relationship to the fraction of the cis isomer in the sample. This curve demonstrates the clear link between the isomeric state of the photoactive unit and the refractive index.The system is photoreversible and Fig. 1 should be seen as representing compositions obtained by both the trans+cis and cis+ trans reactions. The latter reaction is achieved, albeit at a slower rate than the former, by optical pumping at 525 nm. For the polymeric films maximum refrac- tive-index change was reached after ca. 10-20 min with an irradiation power of ca. 0.12 mW cm-2. Fig. 2 shows the effect of changing the levels of substitution of the photoactive units upon the maximum refractive index that can be achieved through the photoinduced changes described above. Clearly, as the level of photoactive units varies so does the concentration of dodecyl units, since within the limits of detection of free Si-H units, p+ q =1 (Scheme 1): this feature leads to variation in the base refractive index.As a consequence, the results are plotted as the deviation induced from the base figure. Over the range of substitution considered here the base refractive index varies from 1.4574 to 1.4888 illustrating the manner by which the final polymer may be tailored to suit a particular application. The most striking feature of Fig. 2 is that relatively small levels of the 1.466 1.465 0 X U .-$ 1.464.-U w *E 0E 1.463 U I I I 1 I I I I 11.462 0 0.2 0,4 0.6 0.8 1 fraction of cis isomer Fig. 1 A plot of measured refractive index at 22 "C of a siloxane- based polymer containing azobenzene units with q =0.05 against the fraction of the cis isomer of the azobenzene unit in that polymer.The series of compositions was prepared by successive irradiation of the polymer with a narrow wavelength band of light centred on 366 nm J. MATER. CHEM., 1991, VOL. 1 0.0p I -0.5 0 7 ;-2.01 .-C 0 03 c2 -3.0 0 0 L I I I-3.51 I 0.0 0.1 0.2 fraction of photoactive units Fig. 2 A plot of the maximum refractive-index change induced through selective irradiation of a series of azobenzene-containing siloxane-based polymers in which the fraction q of the photoactive units is varied photoactive unit are required to give significant and useful changes which may be exploited in an optical space switch.I5 In fact, increasing the level of the photoactive units appears to result in a slight decrease in effectiveness and of course raises the base index above that of silica.An equivalent system in which the unbound chromophore was dissolved in toluene showed refractive-index changes linear with chromophore composition.16 In all cases the changes induced are reversible either through optical pumping or through thermal excitation. In practice, the photoinduced refractive-index changes are relatively stable with time because of the slow thermally driven cis-trans conversion. In summary we have designed and synthesised some novel siloxane-based materials with tailored low base refractive indices, in which the refractive index may be controlled optically in a reversible and significant manner. It is possible to construct from these photoactive polymers optically stimu- lated optical-fibre s~itches'~~" with potential use in optical switching and processing systems.This work was funded by British Telecom. References 1 M. F. Digonnet and H. J. Shaw, IEEE J. Quant. Electron., 1982, QE18, 746. 2 C. Dahne and A. Harmer, Electron. Lett., 1980, 16, 674. 3 P. Yennadhiou and S. Cassidy, Electron. Lett., 1987, 23, 1385. 4 N. J. Moll and D. Dolfi, App. Optics, 1983, 22, 2944. 5 M. B. J. Diemeer and W. J. De Vries, Electron Lett, 1988,24,457. 6 E. S. Goldburt and P. St. J. Russell, Appl. Phys. Lett., 1985, 46, 338. 7 S. A. Cassidy and P. Yennadhiou, ECOCILAN, 1988,88,43. 8 R. Anderson, R. Arkles and G. L. Larson, Silicon Compounds Register and Review, Petrarch Systems, 1987. 9 J. Griffiths, Colour and Constitution of Organic Molecules, Aca-demic Press, London, 1976. 10 S. H. Barley, A. Gilbert and G. R. Mitchell, Makromol. Chem., 1991, in the press. I1 A. Hajaiej, X.Coqueret, A. Lablache-Combier and C. Loucheuz, Makromol. Chem., 1989,190, 327. 12 G. Nestor, M. S. White, G. W. Gray, D. Lacey and K. J. Toyne,Makromol. Chem., 1987, 188, 2759. 13 A. Shukurov, S. D. Nasirdinov, A. G. Makhsumov and N. N. Edganov, Zh. Obschch. Kim., 1986, 56, 2579. 14 A. Proctor, A. Gilbert and G. R. Mitchell, Makromol. Chem., submitted. 15 G. R. Mitchell, S. Cassidy, S. H. Barley and A. Gilbert, to be submitted. 16 S. H. Barley, A. Gilbert and G. R. Mitchell, to be submitted. 17 UK Pat. Application UK9014445.2. Communication 0105515H; Received 7th December, 1990

ISSN:0959-9428    

DOI:10.1039/JM9910100481

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991,1(3), 483-484 Simple and Convenient Method for Preparing Functionalised Network Organopolysilanes Hamao Watanabe,* Minoru Abe, Katsumi Sonoda, Morihiko Uchida, Yuko lshikawa and Makoto lnomiya Department of Chemistry, Faculty of Engineering, Gunma Universitx Kiryu, Gunma 376, Japan A new type of organosilicon polymer, network organopolysilanes bearing methoxy functional groups on the polysilane framework, has been produced via the catalytic redistribution polymerisation of methoxydisilanes which were prepared using the 'pot-residue' disilane fraction in direct synthesis. Keywords: Organosilicon polymer; Functionalised network; Catalytic redistribution polymerisation Much attention has been focused on polysilanes which are accessible via Wurtz-type coupling reactions, homo- and co-polymerisation, of a variety of dichlorodialkyl- and/or di- chloroalkylaryl-silanes.These polysilanes, despite having only limited variety of structure owing to the linear backbone, have recently been shown by many workers to have versatile properties useful for functional materials in high-technology as photoresists, organic photo- and semi-conductors, ceramic precursors, non-linear optical materials, etc. Polysilanes con- sisting of functionalised and/or network structures can be expected to show a variety of unique physical and chemical properties different from those of the linear polysilanes. How- ever, only a few reports on such polysilane structures have appeared so far.' Previously, we have reported that the reactions of sym-methoxymethyldisilanes, (MeO),Me6 -,,Siz (n=4, 2),2 with sodium methoxide gave the first functionalised silanide anions, (Me0)'MeSi-and (MeO)Me2Si-.3 Also, we fond that sym-dimethoxydisilane (n=2) undergoes a catalytic redistribution reaction, giving a series of a,o-dimethoxypermethylpoly-silanes, from which, in the presence or absence of certain reagents, various products, such as a-hydro-o-methoxypoly- ~ilanes,~cyclopolysilanes,5 tetrasilacyclo- and disilacyclo-hexane6 derivatives, trisilacyclo-pentene6 and -pentane7 derivatives, were formed.It has been unequivocally demon- strated that these products can be produced through the reaction of methoxypermethylpolysilanide anion intermedi- ates, MeO(MezSi),Me2Si-, derived from a,o-dimethoxyper- methylpolysilanes by the action of an NaOMe cataly~t.~ As a continuing study of the series of the reactions men- tioned above, we report here the first simple method for preparing a new type of organopolysilane having func- tionalised network systems by using methoxylated disilanes as the starting materials, (MeO),,Me6-nSi (n=4, 3 and a mixture of the two).' Simultaneously, in view of the effective utilisation of disilane resources formed as the by-products in the direct synthesis of methylchlorosilanes, we were able to convert successfully the disilane fraction in the 'pot-residue' (C1,,Me6-,Siz; b.p.150-160 "C) into more usable materials in high-technology fields. The catalytic redistribution reaction of these disilanes was exothermic and proceeded readily in a no-solvent system or in tetrahydrofuran (THF) (Scheme 1).This produced polysilanes as a white or pale-yellow solid which is soluble in the usual organic solvents as has been generally shown in linear polysilanes. Typically, a mixture of la (5 g, 24mmol) and NaOMe (2 mol% relative to la) was stirred under nitrogen for 24 h, during which time the mixture was kept at 40 "C after the end of its exothermic reaction. Addition of a catalyst quencher (an excess amount of 1-chloro-2,3-epoxypropane) and then 'pot-residue' CI,Me,-.si, "Si,-CI,Me,-(n=4+3) (n= 4 and 3) methoxylation (MeO),Me,-,Si, 1 a n=4 b n=3 c n=4+3 Scheme 1 polysilanes catalyst A MeONa B Bu'OK C H,NLi D BuLi E Na toluene (15 cm3) gave a light green-yellow mixture, from which the insoluble material was separated by centrifugation to leave a toluene solution.The solution was evaporated to dryness in U~CUOto give a pale green-yellow powder of 2a (0.77 g, 16% relative to la employed). The toluene-insoluble material was mixed with absolute methanol (15 cm3) and centrifuged to give a white powder, on drying in U~CUO(0.16 g, Table 1 Catalytic polymerisation of disilanes polymer disilane" catalyst (mol%)b solvent' time/h quencherd no. %' ~~ i 24 ClEP 2a(l) 16 11 4 BrEP 2a(2) 14 i 24 BzCl 2a(3) 11 1 24 ClEP 2a(4) 15 1 24 ClEP 2a(5) 10 i 24 ClEP 2a(6) 20 11 4 ClEP 2a(7) 15 i 24 ClEP 2a(8) 19 11 2 ClEP 2a(9) 16 1 24 ClEP 2a(10) 11 11 4 BzCl 2a(ll) 12 i 24 BzCl 2b(12) 23 11 24 BzCl 2b(13) 20 i 24 BzCl 2c(14) 30 11 24 BzCl 2c(15) 24 "About 5 g (24 mmol).'Relative to the disilane employed. 'i, None; ii, THF (15 cm3). dCIEP, I-chloro-2,3-epoxypropane;BrEP, l-bromo- 2,3-epoxypropane; BzCI, benzyl chloride. 'Relative to the disilane employed. See ref. 6. BPrepared by methoxylation of Clz MeSiSiMe,Cl obtained from a disilane fraction, see ref. 8 [scheme (l)]. hA mixture of (MeO),MeSiSiMe(OMe),: (MeO)Me,SiSiMe(OMe), =63 :37 (b.p. 38-49 "C at 0.1 mmHg) prepared from a disilane fraction (b.p. 150-160 "C), see ref. 2. J. MATER. CHEM., 1991, VOL. 1 Table 2 Characteristics of selected samples of polysilanes polymer appearance M," MWIM" MeSi :0Meb pale- yellow powder 56 700 7.5 3: 1 72 200 9.3 3: 1 48 500 9.5 3: 1 71 300 10.3 e pale- yellow viscous liquid I100 1.2 10: 1 1600 1.3 6: 1 1300 1.3 3: 1 1500 1.3 8: 1 ceramic yield (%)f 80 75 70 e e e e e "GPC method; polystyrene standards.*Methyl hydrogen ratio by 'H NMR method. 'After heating from 40 to 1000 "C at a rate of 10 "C min-' in N,. dPolymer 2a sometimes changes insoluble in organic solvents after standing for several weeks. 'Not determined. 3.2% of 3a). Similarly, the reactions to produce the poly- silanes were carried out in THF solution, removal of the sol- vent in uucuo was made after quenching the catalyst and the subsequent treatment for the resulting mixture was similar to that of the above reaction.Thus, three types of polysilane, 2a, 2b, and 2c, were produced in the presence of catalysts from the corresponding starting materials, (MeO)2MeSiSiMe(OMe)2(la), (MeO)2MeSiSiMe2(OMe)(lb), and a mixture of la: lb=63 :37 (lc) (Table 1). The characterisation of the products was carried out in the usual manner. A sample of 2a, for example, showed IR absorption bands at ca. 1080(SiOMe) and 1250(SiMe) cm- ', 'H NMR broad peaks at 3.5 (centre, OCH,) and 1.0-O.l(SiCH,)ppm in a ratio of 1 :3, "Si NMR signals of several unresolved peaks near -80 ppm, and UV-VIS band rising from near 400 nm, which increases in intensity with decreasing wavelength.? These results suggest that the struc- ture of the sample is a network systemIb to which the methoxy groups are attached (Table2).Also, the polymer was found to be amorphous by X-ray diffraction. Thermogravimetric analyses of polysilane 2a (40-1000 "C; heating rate, 10 "C min-' in N2) were performed and the weight losses were <30% in all samples tested. With respect to the reaction pathway for the formation of the polymers, e.g. for 2a, it is likely that polysilanyl anions arising from the scission of permethoxymethylated polysilanes by the catalyst play an important role in the propagation leading to the network structure, chain elongation, branching and bridging between chains, accompanied by the regener- ation of metal methoxide in the catalytic cycle.4 t Absorptions in the region of ,I=350-250 nm increased by a factor of E =ca.103-10" (cyclohexane solution) per (MeSi),(OMe) unit. Finally, it should be emphasised that the present study opens up the way for the simple and convenient conversion of the disilane 'pot-residue' into more valuable forms; in particular, new types of organopolysilane with versatile properties as functional materials were produced. In addition, the polysilanes thus formed could have their structures and properties modified by replacing the methoxy or methyl groups in OMe substituents with others via the use of nucleo-philes (Grignard reagents and alkyl metals) or electrophiles (alkyl halides, etc.). References 1 (a) R. H. Baney, J. H. Gaul Jr.and T. K. Hilty, Organometallics, 1983,2,859;(b) R. A. Bianconi, F. C. Shilling and T. W. Weidman, Macromolecules, 1987, 22, 1697; (c) K. Furukawa, M. Fujino and N. Matsumoto, Macromolecules, 1990, 23, 3424. 2 H. Watanabe, M. Kobayashi, Y. Koike, S. Nagashima, H. Matsumoto and Y. Nagai, J. Organomet. Chem., 1977, 128, 173. 3 H. Watanabe, K. Higuchi, M. Kobayashi, M. Hara, Y. Koike, T. Kitahara and Y. Nagai, J. Chem. SOC., Chem. Commun., 1977, 534. 4 H. Watanabe, K. Higuchi, T. Goto, T. Muraoka, J. Inose, M. Kageyama, Y. Iizuka, M. Nozaki and Y. Nagai, J. Organomet. Chem., 1981, 218, 27. 5 H. Watanabe, K. Higuchi, M. Kobayashi, T. Kitahara and Y. Nagai, J. Chem. SOC., Chem. Commun., 1977, 704. 6 H. Watanabe, J. Inose, T. Muraoka, M. Saito and Y. Nagai, J. Organomet. Chem., 1983, 244, 329. 7 H. Watanabe, J. Inose, M. Kameyama, M. Saito and Y. Nagai, J. Chem. SOC., Chem. Commun., 1982, 1366. 8 H. Matsumoto, T. Motegi, M. Hasegawa and Y. Nagai, J. Organomet. Chem., 1977, 142, 149. Communication 1/01414E; Received 25th March, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100483

出版商:RSC    

年代:1991

数据来源: RSC

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J. MATER. CHEM., 1991, 1(3), 485-486 485 Synthesis and Optical Spectroscopy of Platinum-metal-containing Di- and Tri-acetylenic Polymers Brian F. G. Johnson," Ashok K. Kakkar," Muhammad S. Khan," Jack Lewis,*a Ann E. Dray,b Richard H. Friend,*b and Felix Wittmand a University Chemical Laboratory, Lensfield Road, Cambridge, UK Ca vendish Laboratory, Madingley Road, Cambridge, UK Optical absorption and photoluminescence measurements on the title polymers, -f-Pt(PBu~),-(C-C),,,-C~C+, (m= 1, 2) show that there is appreciable n-electron conjugation extending through the metal sites on the chain, with a lower n-n* energy gap for the triacetylenic than for the diacetylenic compound. Keywords: Optical absorption; Photoluminescence; Polyyne polymers; Vibronic Transition-metal a-acetylide complexes of the Ni triad ~M(PBu?)),-C=C-(R),-C=C+~ (where M =Ni, Pd, Pt; R=p-C,H,; rn=0, 1; Bu=butyl), first developed' by Hagihara's group, are of great interest owing to their potential applications in the new materials industry.We have recently reported that bistrimethyltin(SnMe3) derivatives of H-C-C-R-C-C-H (R =P-C6H4; P-C6H4-P-C6H4) are versatile reagents to a diverse range of transition-metal polyalkyne polymer^.^-^ Using this new synthetic route, we have now prepared the di- and tri-acetylenic platinum (Pt) polymeric complexes, fPt(PBu",), -(CZC),,,- C=C +n (rn=1, 2). Although, the diacetylenic Pt polymers have been reported previously' by the reaction of trans-di(butadiynyl)bis(tri-n-butylphosphine)platinum(II) [(PBu?)),Pt(-C-C-CfC-H)),] with dichlorobis(tri-n-but ylp hosp hine)platinum(xI) [P t( PBu:)~ Cl J, the correspond- ing triacetylenic polymers are unknown.The latter have been suggested6 to be of great importance in the studies related to non-linear optical properties of these systems. There is also considerable interest in the electronic structure of the ground and excited states of the polyyne chain7v8 and we consider that these compounds, especially the triacetylenic polymers, provide an important experimental realisation of the delocal- ised polyyne n-electron system. In this communication we wish to describe synthesis and a preliminary investigation of the optical spectra of these polymeric materials. A general synthetic route (Scheme 1) to the polymeric species requires the addition of 1 equivalent of platinum complex, [Pt(PBu",),Cl,] (1) to 1 equivalent of bis(SnMe,) reagents 2 or 3.t A systematic characterization1 of these complexes was achieved by analytical and spectroscopic methods (IR; 'H, 13C, and 31PNMR) and molecular weight determinations.The weight-average molecular weight (M,) values§ for the polymeric compounds (130 000 for 4 and 160 000 for 5) show a high degree of polymerisation. t The bis(SnMe,)acetylides [Me3Sn -C C-C=C-SnMe, (2) and Me,Sn -CrC-C= C -Cr C -SnMe, (3)] were synthesised by adaptation and modification of the literature procedure^.^ $ (i) Selected data for 4. Calc. for CzsH54PzPt: C, 51.92, H, 8.40; P, 9.56%. Found: C, 51.89; H, 8.47; P, 9.47%.M,= 130000 (n,= 200). v,,, 1999 cm-' (C=C); "P{'H} (CD,Cl,, 162 MHz) 6, 136.6 (J,-,=2381 Hz); 'H(CD,C12, 400 MHz) dH 0.92, 1.44, 1.51, 2.01. (ii)Selected data for 5. Calc. for C,,H,,P,Pt: C, 53.63; H, 8.10%. Found: C, 52.78; H, 8.12%. Mw=160000 (nw=238).v,,, 2096cm-' (C-C); 31P('H} (CDZCl2, 162 MHz) 6, 136.3 (Jpt-p=2300 Hz);13C{1H} (CD2Cl2, lOOMHz) 6, 13.8, 24.1, 24.5, 26.5, 59.5, 81.5, 89.4; 'H (CDZCIZ, 400 MHz) 6H 0.93, 1.43, 1.51, 2.00. 0 Molecular weights were determined by Gel Permeation Chroma- tdgraphy (GPC) method. For GPC procedural details see ref. 10. High solubility of these polymers in common organic solvents allows preparation of samples suitable for physical measurements. Optical absorption spectra were obtained from dilute solutions in dichloromethane, and the photoluminesc- ence (PL) measurements were performed on thin films of the polymers which were spin-coated onto spectrosil substrates from solutions in toluene.Excitation was provided by the quadrupled output (266 nm) from a Q-switched Nd :YAG laser, and measurements were made at low temperatures (<30 K) in order to maximise the PL output and to maximise the sharpness of the PL features. The results of this study are presented in Table 1. Both polymers show strong absorption with well resolved structure which we ascribe to the n-n* transitions associated with acetylenic units of the chain. The minimum excitation energy is lower for the triacetylenic polymer (2.7 eV) than for the diacetylenic polymer (3.0 eV).This provides direct evidence for the role of the length of the polyyne chain in determining the energy gap. One of the particular advantages of working with the polyyne spacers between the metal sites (in distinction with earlier work".'2 on more complicated spacers such as -C~C-c6H4-C-C-) is that the vibrational spectrum of the chain is particularly simple, with a single vibrational mode coupling to the bond dimerisation amplitude; this is the -C=C-stretch frequency at ca. 2250cm-' (= 0.27 eV).t This accounts for the well resolved structure in the absorption spectra, which is due to transitions from ground to excited electronic state coupled with transitions to the various vibronic levels of the excited state.As listed in Table 1, many of the energy spacings for all materials studied here are close to 0.27 eV. We expect that the excited states of the n-electron system will be excitons, and that these will be localised, probably to within no more than one or two repeat units of the hai in,^.^ and we can expect to see radiative decay of the singlet excitons. The measured PL spectra are characteristic of the decay of such excited states, and we see very well resolved bands corresponding to the different levels of the vibrational modes of the ground electronic state; we find again that the energy separation of the PL bands is close to 0.27 eV in most cases. The strong vibronic coupling to the electronic transitions, and substantial Stokes' shift between the strongest bands in the absorption and emission spectra (ca.0.75 eV) indicates that there is strong coupling between the n-electron system and the carbon-carbon bond dimerisation amplitude. We t CEC triple-bond stretch, see ref. 13. J. MATER. CHEM., 1991, VOL. 1 SnMe3-C=C-C=C-SnMe3(2) Pt~PBU~~,C,, SnMe,-C=C-C=C-C=C-SnMe, (3) 1 equiv., toluene, 30"C, 1 h. (11 PBu; PBu; fPt-C=C-C=C* fpt-c~c-c=c-c=c+ Scheme 1 Table 1 Optical absorption and photoluminescence results for polymers 4 and 5 maxima in absorption maxima in luminescence spectrum/eV spectrum/eV polymer 4 ~P~(PBU;)~-(C=C),+~ 2.96, 3.22, 3.48 2.07, 2.34, 2.61 polymer 5 fP~(PBU;)~-(C=C), -3n 2.74, 3.11, 3.38, 3.66 1.88, 2.09, 2.37 infer from this that the dimerisation amplitude for the excited 2 S.J. Davies, B. F. G. Johnson, M. S. Khan and J. Lewis, J. Chem. state is considerably weaker than that for the ground SOC., Chem. Commun., 1991, 187. state (butatrienic, C=C=C=C, or hexapentaenic, 3 S. J. Davies, B. F. G. Johnson, M. S. Khan and J. Lewis, J. Organomet. Chem., 1991, 401, C43.c=c=c=c=C=C). 4 B. F. G. Johnson, A. K. Kakkar, M. S. Khan and J. Lewis, In conclusion, Pt-metal-containing di- and tri-acetylenic J. Organomet. Chem., in the press. polymeric complexes are now accessible in good quantities, 5 K. Sonogashira, S. Takahashi and N. Hagihara, Macromolecules, and their high solubility in common organic solvents allows 1977, 10, 879. one to examine their physical properties.The electronic 6 S. Guha, C. C. Frazier, P. L. Porter, K. Kang and S. E. Finberg, Optics Lett., 1989, 14, 952.properties of these complexes are determined by the delocal- 7 G. R. Williams, J. Phys. C., 1988, 21, 1971.ised n-electron system along the polymeric chain. A detailed 8 S. R. Phillpot, M. J. Rice, A. R. Bishop and D. K. Campbell,investigation of the electronic structure, conductivity and non- Phys. Rev. B, 1987,36, 1735. linear optical properties of these and related polymers is 9 G. Zweifel and S. Rajagopalan, J. Am. Chem. SOC., 1985, 107, currently in progress. 700; H. Bock and H. Seidl, J. Chem. SOC. (B), 1968, 1158. 10 Organometallic Polymers, ed. S. Takahashi, M. Kariya, T. Yatake, We would like to thank NSERC of Canada for a postdoctoral K. Sonogashira and C. U. Pittman Jr., Academic Press, New York, 1978.fellowship to A. K. K., SERC for support to M. S.K. and 11 A. E. Dray, F. Wittmann, R. H. Friend, A.M. Donald, M. S.A. E. D., and Dhaka University (Bangladesh) for study leave Khan, J. Lewis and B. F. G. Johnson, Proc. Znt. Conf: Synth. (M. S.K.). We would also like to thank Professor Todd B. Met., Tubingen, Sept., 1990. Marder of University of Waterloo (Canada) for helpful dis- 12 A. E. Dray, F. Wittmann, R. H.Friend, A.M. Donald, M. S. cussions and Dr. Elizabeth Meehan (Polymer Laboratories, Khan, J. Lewis and B. F. G. Johnson, Synth. Met., in the press. UK) for molecular-weight determinations. 13 R. M. Silverstein, G. C. Bassler and T. C. Morrill, Spectroscopic Identification of Organic Compounds, Wiley, New York, 198 1. References Communication 1/01499D Received 28th March, 1991 N. Hagihara, K. Sonogashira and S. Takahashi, Adu. Polym. Sci., 1980, 41, 149.

ISSN:0959-9428    

DOI:10.1039/JM9910100485

出版商:RSC    

年代:1991

数据来源: RSC

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J. MATER. CHEM., 1991,1(3),487-488 BOOK REVIEWS Cambridge Topics in Mineral Physics and Chemistry Vol. 1. Phase Transitions in Ferroelastic and Co-elastic Crystals. Ed. E. K. H. Salje. Cambridge University Press, Cambridge, 1990. Pp. xvi +366+ xlviii +iii. Price €50.00 (Hardback) One of the great problems in the mineralogical sciences is the complexity of the phase-transition behaviour shown by very common natural materials such as the feldspars. Our under- standing of such transitions has been revolutionised over the last few years by the application of Landau theory to these systems. It has become apparent that the different ordering and distortional processes involved in the transitions, their interactions, and even the pressure and temperature variation of properties such as heat capacity and birefringence away from the transition point, can be readily rationalised and accurately modelled. The concepts involved are more familiar in solid-state chemistry and physics than in classical mineralogy.This timely book is therefore divided into two parts. The first 12 chapters (Salje) constitute an extended review of the necessary theory. The second half is a collection of case studies by various authors, illustrating the application of the theory to different problems. The title of the book is perhaps unfortunate, making it appear rather more specialized than it actually is. However, many observed phase transitions, probably the majority of them, can be described in terms of symmetry change from group to subgroup or vice versa.As Hatch and Stokes state (ch. 19), ca. 8 1YOof all possible space group-subgroup tran-sitions can exhibit some form of associated elastic behaviour, bringing them within the scope of this book. The solid-state science is undeniably good. The systems discussed range from the petrologically important (plagioclase, leucite) to the technologically important (high- T, supercon-ductors) to simple molecular materials (SFs, CHBr,). The two main aspects of the book which invite comment are the presentation and the intended audience. The first 12, didactic chapters are bracketed by helpful introduction and summary paragraphs. However, they are marred by careless proof-reading. For instance, Equation 10.19, featuring a 24th degree polynomial, is derived from ‘Equations 10.4.5 and 10.4.6‘ which do not exist as such! They are certainly not to be found further on, in Section 10.4.They are in fact Equations 10.12 and 10.13, in Section 10.3. Indexing and referencing problems abound. Chapter 13 (Giittler) discusses the application of infrared spectroscopy to the transitions in the important minerals cordierite and albite. No mention of cordierite is to be found in the index, and albite does not appear in this context. Appendix Table2 is an extensive compilation of phases showing ferro- and co- elastic transitions, with references. Although useful, it is clearly not comprehensive since it does not include HCN, reviewed by Dove (ch. 18).It is asserted in the preface that Part 1 ‘essentially forms a textbook on the subject and can thus be used for teaching or learning at mainly an undergraduate level’. Unfortunately, it cannot be said that this aim is entirely satisfied by the present edition. There is a general tendency to pull equations out of thin air (or to give references to journals) in Part 1, with minimal in situ explanation of fundamentals. This is further compounded by the proof-reading errors noted above, the whole generally militating against use as a textbook by second-year undergraduates. There is also the problem of which undergraduate course could best assimilate this subject matter. Physics or chemistry students are likely to be confused by the structurally complex mineralogical systems on which the book concentrates.Earth scientists will wonder at the assumed prior knowledge of group theory and elastic theory. No attempt has been made to discuss geological ramifications of the mineral behaviour that is described. Above all, one is forced to question whether the time required to master phase transitions at this level is wisely spent during a 3-year degree course, at the expense of a broader overview of a discipline. All that said (mainly, it must be confessed, owing to an unguarded claim in the preface), the fact remains that this is a most welcome addition to the tertiary solid-state literature. The book deals expertly with complex issues that are all too commonly avoided, and which deserve wider exposure.This book will undoubtedly provide the basis for stimulating interdisciplinary postgraduate courses, and should also be a welcome addition to any Physics, Chemistry, Earth Science or Materials Science library. In the long term its influence is likely to be considerable. D. M. Adams A. G. Christy Received 27th March, 1991 Introduction to Polymer Dynamics. by P. G. de Gennes. Cambridge University Press, Cambridge, 1990. Pp. vi +58. Price p/b S6.95, h/b €20.00. This is a gem of a book and is recommended reading for all who are interested in a fundamental understanding of polymer behaviour. The book is based on a course of lectures given at the Polytechnic of Milan in 1986 and focuses attention on basic concepts in the behaviour of polymers without involving the more advanced mathematical formalism found in the larger, established texts.It is short, containing only some 58 pages, including the index, and the choice of material is clearly highly selective, reflecting some of Professor de Gennes’ own special interests. Nevertheless, the author is able to illustrate the rich variety of behaviour in these practically important materials and to show that many of the properties can be at least qualitatively understood with fairly simple ideas. Potential readers should, however, not take the title too literally: it is not so much an introduction as a short and highly stimulating overview. A newcomer to the field will find it useful to keep one of the more established texts (such as the same author’s Scaling Concepts in Polymer Physics) close to hand for frequent reference. What makes the book so stimulating (and successful) is not rigorous theoretical treat- ment but the stamp of Professor de Gennes’ own unique style, seeking wherever possible to explain complex phenomena in the most straightforward and transparent way.Each chapter ends on an up-beat, emphasising the oppor- tunities for new research that remain in polymer dynamics. References are provided at the end of the book. Chapter 1 is concerned with general concepts as applied to the motions of polymer chains in solvents and in melts such as diffusion and internal deformation modes, and there are also brief mentions of viscoelasticity, reptatation and chemical kinetics in entangled media.The treatment is brief but critical. Chapter 2 is concerned with the application of simple statistical ideas to examine the possible conformations of proteins around an active site. In a protein the hydrophilic amino acids can act as specific receptors at an active site, but of course they are linked together by relatively long loops of the peptidic chain. There is considerable interest in estimating the minimum size required for these loops for a given active site. Chapter 3 is not specifically concerned with polymers but does feature a discussion of the dynamics of dry spreading of liquids on solids. Polymers and 4He are picked out as special cases of fluids where there are still important questions concerning spreading properties! It is well known that flexible polymers in dilute solution can reduce turbulent losses in a flowing fluid.This is quite a complex phenomenon, however, involving the coupling between hydrodynamic aspects of turbulence and the visco- elastic behaviour of polymer chains. In Chapter 4, which is the longest, the author shows that many features of the problem can be understood by emphasising the elastic and not the viscous response of a polymer chain. Again the approach is fairly qualitative, but presents useful insights for the guidance of future experiments. J. H. R. Clarke Received 1lth April, 1991 Springer Proceedings in Physics. Ed. H. K. V. Lotsch. Vol 51:The Physics and Chemistry of Organic Superconductors.Proceedings of the ISSP International Symposium, Tokyo, Japan, August 28-30,1989. Ed. G. Saito and S. Kagoshima. Spri nger-Verlag, Berlin-Heidel berg-New York-London-Paris-Tokyo-Hong Kong, 1990. Pp. xxii +476. Price DM 114.00. ~~ ~~ The field of superconductivity waxes and wanes. The organic molecular variety, comprising modest-sized components (ET adducts and the like) have not exceeded the elemental or elemental-alloy systems in the critical transition temperature T,, but they have provided a vast increase in scope for the study of superconductivity. Complexes with the DMIT ligand form a companion group. These acronyms are not helpful to the neophyte but then this is not an introduction to the subject, it is the proceedings of an international symposium.The conference title had clearly been chosen before Bednorz and Muller upstaged the particular area named, with T, in the low teens, by introducing the ceramic oxocuprate class with Tc>125K, and the introductory contributions to the proceedings cope with this by comparative reviews of the organic and inorganic systems. To quote, ‘the nature of the pairing interaction remains an open question in organic superconductors .... However, a non-phonon-mediated pairing mechanism [is] quite plausible.’ The several reviews are excellent in providing the contexts for the papers that follow. The papers, reprinted from camera- J. MATER. CHEM., 1991, VOL. 1 ready copy, are a mixture of research with extensive review material of the contributors’ own work.Theoretical and experimental work leads to predictions of desiderata which can only be deemed ‘hopeful’. This rnklange is again not for the neophyte. Many papers cover systems which should, or might, be superconductive; some comprise organic prep- arations only. However, a final summary by Ishiguro makes a useful framework and I, for one, benefited by reading this early rather than last, even if it does provide more of an index than a conflation of views. The conference sections were: I, Organic Superconductors- Overview and Comparison with Oxide Superconductors (three papers); 11, Metal Coordinated Organic Conductors and Related Materials (nine papers); 111, TMTSF Family- Superconductivity and Spin-Density Waves (11 papers); IV, BEDT-TTF Family-Superconductivity (1 6 papers); V, BEDT-TTF Family -Fermiology and Related Subjects (10 papers); VI, DMET Salts and their Families (five papers); VII, Crystal and Electronic Structures (18 papers); VIII, Structural Design of Organic Superconductors (four papers); IX, New Molecules and Materials (17 papers); X, Theory (nine papers).The authorship is suitably international, some two-thirds being of host-country origin. It was intriguing to see work on, for example, Langmuir-Blodgett films included. Many of the systems reported were ‘might have beens’, a fair fraction are metallic rather than superconducting, and some not even that. What is to be said by way of special commendation? This is another milestone (of many) on the route to ever increasing understanding of the solid state, particularly superconduc- tivity; to cite particular names would be invidious, but the expected workers from both East and West have contributed.In a generalisation on the field, one must say that not a great deal of the development of superconductivity studies on the organic systems was responsible for leading directly to the discovery of the inorganic oxocuprate superconductors; how- ever, with hindsight, parallels can be drawn in the behaviour of the two classes. Following Day’s review, these are the importance of low dimensionality and the proximity of mag- netic and superconducting states tunable by pressure or chemical composition, consequences of both classes being narrow-band systems. For those interested and practising in the field, this is an interesting read in parts; clearly, to learn about the oxocuprate systems, one must read elsewhere. Three groups of superconductive materials have now been established: elemental metals and their alloys, organic adducts and most recently the oxides. What next? All I can say is: watch this space (or the adjoining). D. R. Rosseinsky Received 1lth April, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100487

出版商:RSC    

年代:1991

数据来源: RSC