摘要:

454 QUARTERLY REVIEWS Stereoregular addition polymerisa- Steric hindrance 2 107; 11 1 Steroidal alkaloids 7 231 Sterols steroids and terpenoids bio- genesis of. Part 1. Biogenesis of cholesterol and the fundamental steps in terpenoid biosynthesis. Part 2. Phytosterols terpenes and the physiologically active steroids 19 168 201 Strengths of organic bases prediction of 18 295 Structure of liquids in relation to their transport properties 14 236 Substituent interactions in ortho- substituted nitrobenzenes 18 389 Substitutions aroma tic nucleoph ilic mechanism and reactivity in 12 1 Sugar epoxides 13 30 Sulphur-fluorine bonds compounds containing 15 30 Sulphur nitride and its derivatives 10,437 Sulphuric acid behaviour of organic compounds in 8 40 Surface chemistry adsorption energy and adsorption equilibria 15 99 Surface compounds the chemistry of carbon-oxygen 13,287 Sydnones 11 15 Synthesis of sesquiterpenes 18,270 Synthetic gemstones 15 1 tion 16 361 Tautomerism of phenols 10 27 Technetium chemistry an outline of 16 299 Terpenes di- and tri- synthesis of 16 117 Tetronic acids 14 292 Theory of charge-transfer spectra 15 191 Thermochemical properties of phos- phorus compounds.17,204 Thermochemistry of the elements of Group IVB and IV comments on 7 103 Thermodynamics of ion association in aqueous solution 14 402 Thermodynamic properties estima- tion of for organic compounds and chemical reactions 9 229 Thermodynamic properties of high polymers and their molecular inter- pretation 1 265 Thermodynamic properties of organic oxygen compounds 15 125 Tin acceptor properties of quadri- positive 17 382 Topotactic reactions in inorganic oxy-compounds 16,343 Tracers radioactive preparation of 2 93 Transformation asymmetric and asymmetric induction 1 299 Transformations related and photo- chemical rearrangements 15 393 Transformations thermal in solids 11 246 Transition metals cyanide complexes of the.16 188 Transition-metal compounds crystal- line electron resistance in 14. 427 Transitions in solids and liquids 3 65 Transport control in heterogeneous reactions 6 157 Transport properties of Iiquids in relation to their structure 14 236 Triplet state 12 205 Triterpenes tetracyclic 9 328 Tropolones 5 99 Tryptophan biological degradation of 5 227 Ultrasonic analysis of molecular relaxation processes in liquids 11 134 Ultrasonic waves effects of on electrolytes and electrolytic pro- cesses 7 84 Vacuum microbalance techniques theory and applications of 19 231 Vapours of the elements 19,77 Veratrum alkaloids 12 34 Vibrational spectra of ionic melts 17 Wittig reaction 17.406 Wool wax constitution of 5 390 X-Ray crystal analysis modern methods of determination of mole- cular structure by and their ac- curacy 7,335 p-Xylylene chemistry of and of its analogues and polymers 12 301 225 454 QUARTERLY REVIEWS Stereoregular addition polymerisa- Steric hindrance 2 107; 11 1 Steroidal alkaloids 7 231 Sterols steroids and terpenoids bio- genesis of. Part 1. Biogenesis of cholesterol and the fundamental steps in terpenoid biosynthesis. Part 2. Phytosterols terpenes and the physiologically active steroids 19 168 201 Strengths of organic bases prediction of 18 295 Structure of liquids in relation to their transport properties 14 236 Substituent interactions in ortho- substituted nitrobenzenes 18 389 Substitutions aroma tic nucleoph ilic mechanism and reactivity in 12 1 Sugar epoxides 13 30 Sulphur-fluorine bonds compounds containing 15 30 Sulphur nitride and its derivatives 10,437 Sulphuric acid behaviour of organic compounds in 8 40 Surface chemistry adsorption energy and adsorption equilibria 15 99 Surface compounds the chemistry of carbon-oxygen 13,287 Sydnones 11 15 Synthesis of sesquiterpenes 18,270 Synthetic gemstones 15 1 tion 16 361 Tautomerism of phenols 10 27 Technetium chemistry an outline of 16 299 Terpenes di- and tri- synthesis of 16 117 Tetronic acids 14 292 Theory of charge-transfer spectra 15 191 Thermochemical properties of phos- phorus compounds.17,204 Thermochemistry of the elements of Group IVB and IV comments on 7 103 Thermodynamics of ion association in aqueous solution 14 402 Thermodynamic properties estima- tion of for organic compounds and chemical reactions 9 229 Thermodynamic properties of high polymers and their molecular inter- pretation 1 265 Thermodynamic properties of organic oxygen compounds 15 125 Tin acceptor properties of quadri- positive 17 382 Topotactic reactions in inorganic oxy-compounds 16,343 Tracers radioactive preparation of 2 93 Transformation asymmetric and asymmetric induction 1 299 Transformations related and photo- chemical rearrangements 15 393 Transformations thermal in solids 11 246 Transition metals cyanide complexes of the. 16 188 Transition-metal compounds crystal- line electron resistance in 14.427 Transitions in solids and liquids 3 65 Transport control in heterogeneous reactions 6 157 Transport properties of Iiquids in relation to their structure 14 236 Triplet state 12 205 Triterpenes tetracyclic 9 328 Tropolones 5 99 Tryptophan biological degradation of 5 227 Ultrasonic analysis of molecular relaxation processes in liquids 11 134 Ultrasonic waves effects of on electrolytes and electrolytic pro- cesses 7 84 Vacuum microbalance techniques theory and applications of 19 231 Vapours of the elements 19,77 Veratrum alkaloids 12 34 Vibrational spectra of ionic melts 17 Wittig reaction 17. 406 Wool wax constitution of 5 390 X-Ray crystal analysis modern methods of determination of mole- cular structure by and their ac- curacy 7,335 p-Xylylene chemistry of and of its analogues and polymers 12 301 225

ISSN:0009-2681    

DOI:10.1039/QR96519FP001

出版商:RSC    

年代:1965

数据来源: RSC

摘要:

MOSSBAUER STUDIES OF CHEMICAL BONDING By J. F. DUNCAN and R. M. GOLDING (CHEMISTRY DEPARTMENT VICTORIA UNIVERSITY OF WELLINGTON NEW ZEALAND) (CHEMISTRY DIVISION DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH WELLINGTON NEW ZEALAND) SPECTROSCOPY is the study of absorption and/or emission of electro- magnetic radiation between two or more energy levels. In optical absorption spectroscopy we examine transitions (ca. 30,000 cni.-l) between the electronic ground state and the excited states; in infrared spectroscopy between vibrational ground and excited states (ca. I000 cm.-l) ; in electron spin resonance spectroscopy between electron spin states arising from the interaction of the magnetic field with the electron (ca. 0.3 cm.-l) ; and in nuclear magnetic resonance spectroscopy between nuclear spin states arising from interaction of the magnetic field with the nucleus (ca.0.002 cm.-’). Mossbauer spectroscopy is simply a study of the absorption of electromagnetic radiation (y-rays) between the nuclear ground and excited states (ca. lo8 cm.-l). Since the first Mossbauer experiments in 1958,l physicists have used the principle in a variety of investigations especially for studying atomic motions in solids.2 However it is only recently that chemists have realised the importance of Mossbauer spectroscopy for examining electronic con- figurations and the structures of chemical compounds. In this Review we discuss only those features of Mossbauer spectroscopy pertinent to chemistry. 1. Fundamental Features Mossbauer spectroscopy is the study of y-ray absorption (or emission) between the ground and excited states (usually the first) of a specific type of nucleus.The energy difference between the ground and excited states of the transition involved is usually 10-100 kev (1 kev = 8.07 x los cm.-l). When an isolated atom emits a y-ray the total momentum of the system remains constant i.e. the recoil momentum of the atom is equal to the momentum of the y-ray E,/c where c is the velocity of light and E the energy of the y-ray when the decaying nucleus is at rest. Thus for an emitted y-ray \ and for an absorbed y-ray Ey’= E o ( l +&). Mossbauer 2. Physik. 1958 151 124; Naturwiss. 1958 45 538. a Boyle and Hall Proc. Phys. Soc. 1962 25 441. 36 DUNCAN AND GOLDING MOSSBAUER STUDIES OF CHEMICAL BONDING 37 The recoil velocity Y depends in general on the thermal motion of the nucleus but when the decaying nucleus is bound in such a way that the recoil momentum is absorbed entirely by the lattice the change in E is negligible and a y-ray spectrum centred at E is obtained (eqn.1). A similar situation obtains when y-ray absorption takes place (eqn. 2). If we now mechanically move the emitter at a velocity v’ the Doppler shift3 in the energy of the emitted y-ray is E,v’/c which corresponds for instance to 4.8 x ev per cm./sec. velocity for the 14.4-kev y-ray emitted in the decay of 57Fe from the first exicted state to the ground state. Since the Doppler shift may be varied by altering the velocity of the source E may be adjusted until allowance has been made for the small difference in the energy level of the first excited state above the ground state in the source compared to that in the absorber (in a chemically different environ- ment).Nuclear absorption of the y-radiation will then occur. 2. Theoretical Aspects As a consequence of the intrinsic nuclear spin 115 (or I in quantum units) the nucleus may interact with magnetic and electric fields in the molecule. These interactions may be represented by the spin-Hamiltonian operator jEp = - hyH.1 + P [(31,2 - 1(1 + 1)) + 5 { I+2 + I-”)]. (3) Here y is the gyromagnetic ratio of the nucleus in a particular state with nuclear spin I ; I+ and I- are step-up and step-down operator^;^ P = e2qQ( 1 - y,)/41(21- l) where eQ the quadrupole moment of the nucleus is non-zero when I > 1 eg is the electric-field gradient parallel to the z axis,5 and (1 - yco) is Sternheimer’s screening factor;6 and r] is the asym- metric parameter of the field-gradient tensor.A magnetic field lifts the degeneracy of the nuclear states into the (21 + 1) Zeeman levels the separations being determined by the magnetic- and electric-field interactions for which MI = I 1-1 . . . . -I + 1 -I. To illustrate the typical energy-level diagram so obtained we can consider the ground (I = Q) and first excited ( I = :) states of the 57Fe nucleus when the magnetic field is parallel to the z axis and the asymmetric parameter q is zero. The spin-Hamiltonian operator now becomes (4) A? = - fiyH,I + P{ 3IS2 -I(I + 1)). The energy-level diagram obtained for the 57Fe nucleus using the constants in Table 1 is shown in Fig. 1. The subscripts ‘g’ and ‘e’ refer to the ground See for example Jenkins and W-hite “Fundamentals of Optics,” McGraw-Hill New York 1950.Griffith “The Theory of Transition-Metal Ions,” Cambridge University Press Cambridge 196 1. Sternheimer Phys. Rev. 1951 84 244; ibid. 1952 86 316; ibid. 1954 95 736. 5 See for example Das and Hahn Solid State Physics 1958 Suppl. 1. 38 QUARTERLY REVIEWS TABLE 1. Nuclear properties of some Mossbauer nuclei. Nucleus Natural Nuclear spin Gyromagnetic ratios abundance (%) Ground state First excited Ground state First excited state state re Y g Ye 3 $0.179 -0.102 Ig 2 - 2.082 f0.448 57Fe 2.25 3 ll9Sn 8.68 t 33.41 0 2 0 & 1-21 Ig7Au 100 2 3 $0.0959 $0.76 3 - 3 166Er - gNPN = k y = p/Z where gN is the nuclear Lande g factor PN the nuclear magneton y the gyromagnetic ratio and p the magnetic moment E t A € I FIG.1. Energy-level diagram for the 67Fe nucleus. LIE is the energy separation of the ground and first excited states. The magnetic-field and the electric-field gradient inter-actions are indicated. (The subscripts ‘g’ and ‘e’ refer to the ground and first excited states respectively.) and first excited states respectively. Similar energy-level diagrams can be obtained for llgSn 125Te 129Xe la9Tm and 171Yb. Knowing the energy levels we may next discuss the intensities of the hyperfine structure of the y-ray absorption spectrum i.e. the transition probabilities between the Zeeman levels. These have been determined from the general theory of multipole radiati~n.~ The angular intensity distribution Iiv(O) for dipole radiation is I M ( 0 ) = Cl(1,l M-m mlIe 1 IgM)12 x { 1 + (3m2 - 2)(3 cos28 - 1)).Here 8 is measured about the axis of quantization the Wigner coefficients ( r e 1 M-m m I Ie 1 I g M ) are known constants and m = 1,0 -1. In Table 2 the relative intensities from the ground to the first excited states and the corresponding relative energies for 57Fe are given. When the ( 5 ) m Fagg and Hanna Rev. Mod. Phys. 1959,31,711. DUNCAN AND GOLDING MOSSBAUER STUDIES OF CHEMICAL BONDING 39 TABLE 2. The relative energies and the relative intensities of transitions between the ground and thejirst excited states for 57Fe. Excited state Ground state Relative energies Relative intensities IM - m> I M ) 1 3 emitting nucleus interacts with magnetic and electric fields the y-ray absorption splits into a six-line spectrum. Provided that the absorber has a single-energy resonance the emission spectrum will also be observed as six lines.The energy separations of these transitions depend on the magnitudes of the two interacting fields. Fig. 2 illustrates the relative separation of the six-line spectrum for various magnetic-field and electric- field gradient ratios which we have evaluated for the 57Fe nucleus taking ye/yg = - 0.572. The relative intensities of the six transitions are indicated. Fig. 2 shows that when the effective magnetic field (H,) is zero and only an electric-field gradient is present at the nucleus the spectrum is a doublet. From eqns. 3 and 4 (or Fig. 2) the intensity ratio is In Mossbauer experiments with polycrystalline compounds relative intensities are calculated by averaging over all angles of 8 the average values of sinV and cos28 being 3 and 8 respectively.Consequently the arms of the doublet arising from the interaction of the electric-field gradient with the 57Fe nucleus in a powdered sample of an iron compound are of equal intensity. Deviations from equality are due to preferred orien- tations in the powdem8 When a magnetic field is present either externally applied or inherent in the material the intensities of the six y-ray absorption (or emission) peaks for a powdered iron or iron complex are in the ratio 3 2 1 1 2 3 and if the nucleus is in a preferred orientation the relative intensitiesg are 3:/3:1:1:/?:3 where /3 = 4/(1 + 2cot28) and0</3<4. Boyle Bunbury and Edwards Proc. Phys. Soc. 1962 79 416. Preston Hanna and Heberle Phys. Rev. 1962 128 2207. 40 QUARTERLY REVIEWS I i I l l I I 1 1 I 0 4 I i 0 7'x x/r I +3 t 2 +I s O + sw 1 r,l U -1- -I -2 -3 FIG.2. Separation of the six-line spectrum for the 57Fe nucleus at different magnetic- field and electric-field gradient ratios ye/yg = - 0.572 x = y&H/2 and y = 3P. 2.1 Internal Magnetic Fields in Molecules.-Internal magnetic fields in atoms and molecules arise through the interaction of the s electrons with the nucleus ; this is mathematically expressed in the spin-Hamiltonian by the Fermi contact term. In the usual symbolism where the effective internal magnetic field at the nucleus H, depends on the time-averaged value of the z component of the electron spin (Sz). There is an additional term in the total spin-Hamiltonian contributing to the effective magnetic-field interaction with the nucleus namely that arising from the interactions between the electron and nuclear spins and the electron angular momentum.This the dipolar term is usually much smaller than the Fermi contact term.1° If the electronic ground state of a lo Golding Mol. Phys. in the press. DUNCAN AND GOLDING MOSSBAUER STUDIES OF CHEMICAL BONDING 41 typical transition-metal ion were truly represented by ( ls2) (2s2) (2p6) (3s2) (3p6) (3d9 [i.e. using the Aufbau principle] the total s-electron spin density at the nucleus would be zero. However large effective magnetic fields have been observed in these atoms.ll Sternheimer suggests6 that the outer unpaired electrons polarise the core electrons to produce a finite s-electron spin density. We may relate this to observed Mossbauer spectra as follows.The Aufbau principle implies that the wave functions of the two electrons in the same s shell have the same radial function and differ only in the electron spin +& or -4 (a or /?). However if there is an odd a-spin electron present then it will experience different exchange interactions with the remaining wspin electrons (including those in the core) from those with the /?-spin electrons. Consequently the a- and /?-spin s electrons will have different radial functions leading to a net s-electron spin density I$,(O) l2 - I$a(0) 12. Thus the electron spin density for closed s-electron shells is not necessarily zero. Abragam et a1.12 define a parameter where Sdenotes the number of unpaired electrons. They showed that for the first transition-metal series x was approximately constant (- 3 atomic units).This leads to an effective magnetic field through the Fermi contact term of -125 kgauss per unpaired 3d electron. Watson and Freeman13 confirmed this constancy of x from free-ion spin-polarised Hartree-Fock calculations. Thus the magnetic field at the nucleus of a transition-metal comporind is very large being about -500 kgauss. is sensitive to the symmetry and nature of the ligands surrounding the transition-metal ion. For example the calculated value of x for the free Ni2+ ion is -3-9413 whereas for the Ni2+ ion in a cubic field it is -3-27;14 the experimental values for internal magnetic fields at the manganese nucleus in Mn2+ ion complexes depend on the ligand,15 as shown in Table 3. The negative core polarisation is usually less than ex- pected but this can be explained by configurational mixing of the The value of TABLE 3.The observed internal magnetic field at the manganese nucleus for several Mn2+ compounds. Ligand H20 F- CO2- 02- S2- Se2- Te2- lHzl (kgauss) 695 695 665 570-640 490 460 420 1960,4,177; Hanna Meyer-Schutzmeister Preston and Vincent ibid. p. 513. l1 Hanna Heberle Littlejohn Perlow Preston and Vincent. Phys. Rev. Letters l2 Abragam Horowitz and Pryce Proc. Roy. Soc. 1955 A 230 169. l3 Watson and Freeman Phys. Rev. 1961 123,2027. l4 Watson and Freeman Phys. Rev. 1960,120 11 34. Van Wieringen Discuss. Faraday SOC. 1955 19 118. 42 QUARTERLY REVIEWS TABLE 4. ally aligned environments. Nucleus Host H (kgauss) Ref. 57Fe Fe - 342 11 16 17 17 17 18 57Fe c o 57Fe Ni 57Fe3-k Y iron garnet 392 (tetrahedral) 57Fe34- Y iron garnet 474 17 18 (octahedral) 59c0 Fe 300 19 61Ni Ni - 170 20 l19Sn Fe - 81 21 l19Sn c o - 205 21 l19Sn Ni + 185 21 lg8Au Fe 1460 22 3dn4sx excited statesz3 into the ground state this effect giving a positive contribution to the effective magnetic field at the nucleus.It is clear that large magnetic fields are present at nuclei as a result of electronic inter- actions. In Table 4 we quote a few typical examples for different Mossbauer nuclei. The nuclear spin will couple with this field but if the electron- spin-lattice relaxation time is shorter than the Larmor frequency of the nucleus then the time-averaged value of the internal magnetic field affecting the nucleus is zero. This is often (but not always) the case when the Mossbauer atom is not in a magnetically aligned lattice (e.g.for paramagnetic substances in the absence of external magnetic fields). Usually for this internal magnetic field to be observed the electronic structure of all the atoms must be spatially aligned e.g. in a ferro- magnetic complex. The six-line spectrum which results has been used to determine effective internal magnetic fields at iron nuclei in various lattices (see Table 4). In a recent study of the Mossbauer spectra of Fe3+ in corundum (a non-magnetically aligned matrix) at 78 0~,230 this character- istic hyperfine structure was observed which implies that the spin relaxation time must be sufficiently long to present a stationary magnetic field at the iron nucleus. In some cases the magnetic behaviour of a substance depends upon the temperature. For instance the Mossbauer spectrum for iron at or above the Curie temperature (773") is a single line indicating no inter- action between the nucleus and any magnetic-field or electric-field gradient.l8 Nagle Frauenfelder Taylor Cochran and Matthias Phys. Rev. Letters 1960 5 l7 Wertheim Phys. Rev. Letters 1960,4,403; J. Appl. Phys. 1960,32 110s. la Alff and Wertheim Bull. Amer. Phys. SOC. 1960 5 428. l9 Dash Taylor Nagle Craig and Visscher Bull. Amer. Phys. Soc. 1961 6 136. 21 Boyle Bunbury and Edwards Phys. Rev. Letters 1960 5 553; Boyle Bunbury 22 Roberts and Thomson Phys. Rev. 1963 129,664. 23 Walker Wertheim and Jaccarino Phys. Rev. Letters 1961 6 98. 23a Wertheim and Remeika Phys. Rev. Letters 1964 10 14. The magneticJield at the nuclei of Mossbauer atoms in magnetic- I;;;\ 364. Wegener and Obenshain Z .Physik. 1961 163 17. Edwards and Hall Proc. Phys. SOC. 1961 77 129. DUNCAN AND GOLDING MOSSBAUER STUDIES OF CHEMICAL BONDING 43 However below the Curie temperature the averaged internal magnetic field is not zero and the spectrum has the characteristic six lines9 with spacings dependent upon the magnetisation of the material.16 2.2 Electric-field Gradients at Nuclei.-Both the experimental quadru- pole interaction P and the internal magnetic field can be determined by fitting the experimental results from a Mossbauer spectrum to the calcu- lated relative energies using energies similar to those shown in Table 2. For example Kistner and S ~ n y a r ~ ~ found an internal magnetic field of 5 10 kgauss and a small quadrupole interaction in antiferromagnetic Fe203. However in diamagnetic and paramagnetic compounds only the quadrupole interaction need appear in the spin Hamiltonian (eqn.3) since the averaged effective internal magnetic field is zero (see above). For 57Fe complexes this leads to doublet Mossbauer spectra with relative intensities as predicted in Fig. 2. The doublet energy separation dE, can be evaluated from eqn. 4 with H = 0. For the 57Fe nucleus so that the term governing the variation of dE, in compounds with the same Mossbauer nucleus is the electric-field gradient (eq) at the nucleus. The energy of Coulomb interaction between the electrons and the protons in an atom can be written as a set of multipole interaction^.^^ The constant term gives rise to the central-field energy and it is of no interest to us here. The dipolar term vanishes leaving the third term the electric quadrupole interaction.The next non-vanishing term is such that interactions from this and higher terms are very small and we shall ignore them. If there is no mixing between the nuclear states then the Hamil- tonian representing the quadrupole interaction can be written as where (r3) is the averaged value of r3 and Z is the nuclear spin. The distance between the hth electron and the nucleus is r,,.26 If we have an 1" electronic configuration then the Hamiltonian (8) may be written2' as e2 Q ( r -3) S f 7/{3(L.1)2 + ; (L.1) - L(L + l)I(I + 1)). (9) xq = * I(2I - 1) Here 24 25 26 27 ~- 21 + 1 - 4s ' = S(21 - 1)(21 + 3)(2L - 1) ' Kistner and Sunyar Phys. Rev. Letters 1960 4 412. Cohen and Reiff Solid State Physics 1957 5 321. Casimir see ref.25. Bleaney and Stevens Reports Progr. Phvs. 1953 16 108. 44 QUARTERLY REVIEWS n 2 S = 4 2 and L = - (21 + 1 - n). The positive sign in this equation is taken when the shell is less than half-filled and the negative sign when the shell is more than half-filled. For the d5 case Fe" I = 2 and n = 5; thus L = 0 and from the Hamiltonian (9) it follows that dE = 0. However for the d6 case Fe2+ L = 2 and thus dEQ is finite. Therefore ionic paramagnetic iron(rr1) complexes will give a single-peak Mossbauer spectrum but ionic ferrous complexes will show a quadrupole splitting (see below). The relative order of magnitude of the quadrupole interactions expected for octahedral iron complexes can be derived simply from the symmetry and multiplicity of the four possible ground states for d5 and d6 configurations by examining the appropriate Tanabe and Sugano2* diagrams arising from the electrostatic and crystal-field interactions.The ground terms arising from the d5 electronic configuration are 6A for the high-spin (Few) and ,T2 for the low-spin (Fern) complexes. The ds electronic configuration yields 5T2 and lA ground terms for the high- spin (Fe2+) and the low-spin (Fen) complexes respectively. We would expect a zero electric-field gradient from a spherical ground state A but not for non-spherical ground wavefunctions such as T2. In the latter case a greater spin multiplicity would produce a greater electric-field gradient. Hence we obtain a semi-quantitative diagram relating the quadrupole moments expected for the four types of octahedral iron Complexes. Fen Fe2+ As discussed later this type of semi-quantitative argument can be used to determine the type of iron complex in symmetrical octahedral fields.The field symmetry may however also be changed by altering the type of ligand in one or more of the co-ordination positions. For example species like [Fe(CN),NOI2- FeCl 2 Fe(o-phenanthroline),(CN), and FeS0,,7H 2O will all have different electric-field gradients because of the symmetry of the ligands nearest to the iron atom. A relationship has recently been found30 between the spin-spin para- meter D obtained from electron spin resonance measurements and the nuclear quadrupole splitting AEQ obtained from Mossbauer experiments. This can be interpreted by means of the theory developed to explain the Tanabe and Sugano J. Phys. SOC. Japan 1954 9 753.Duncan and Golding I.U.P.A.C. meeting August 1964. so Nicholson and Burns Phys. Rev. 1963 129,2490. DUNCAN AND GOLDING MOSSBAUER STUDIES OF CHEMICAL BONDING 45 zero-field splitting in 3d5 ions. It has been known for some time that the ground state of ions such as Mn2+ and Fe3+ is split even in the absence of a magnetic field (zero-field splitting). This is usually represented by the spin- Hamiltonian 2 = D(S,2 - Q S(3 + 1)) + E(Sz2 - Sy2) (1 1) where D and E are two experimentally determined parameters. Pryce31 suggested that the splitting in Mn2+ arises from spin-spin coupling of unpaired electrons and also from the electric-field gradient. Using these assumptions Chakra~arty~~ has derived expressions for D and E namely D = - !g2p24 (ao3/e)(DD) and E = - 4 g2p2Tq(a,3/e)(EE) (12) (13) where g is the Landk splitting factor 16 the Bohr magneton and a, the Bohr radius.The parameters ( D D ) and (EE) were determined by using hydrogen-like wavefunctions. These expressions lead to the empirical linear relationship discussed by Nicholson and Burns :30 D = Do + keqQlh (14) in which k is an experimentally determined constant. Chakra~arty~~ plotted the variation of D with eqQ/h for Fe3+ ions in several crystal lattices using eqQ/h values determined by Nicholson and Burns.30 This yields D = 0 when q = 0 which is expected when an ion is in a perfect cubic crystal-field. Any deviation from the spherical symmetry of this crystal field is reflected in the magnitudes of D E and q. 2.3 Isomeric or Chemical Shift.-In this section we are interested in small variations in the energy differences between the ground and first excited states arising from the environment of the nucleus.B ~ d m e r ~ ~ showed that this energy difference dE is d E = F(Z) I#s(O) l2 (15) where F(2) is a complex function of a number of nuclear parameters including 2 the nuclear charge Rn is the radius of the equivalent uniform charge distribution; 8Rn is the difference between the radii of the ground and the first excited states ; and I #,(O) I2 is the total s-electron density at the nucleus. d E is thus a measure of the s-electron density which in turn de- pends upon the number of unpaired electrons and the nuclear environ- ment. Mossbauer results are normally related to a reference emitter by defining the isomeric or chemical shift 8 as 8 = F(Z) sRrJRn( I+AO) I i - I #AO> I )s (16) 81 Pryce Phys.Rev. 1950 80 1 107. sa Chakravarty J. Chem. Phys. 1963,39 1004. 33 Bodmer Nuclear Phys. 1961,21 347. 46 QUARTERLY REVIEWS 02- where Il/ls(0)li and ll/ls(0)li refer to the s-electron densities of the absorber and the emitter respectively. Hence both the isomeric shift and the internal magnetic field discussed previously depend upon the total s-electron density at the nucleus. The expected variation in isomeric shifts may be interpreted in a manner similar to that used in discussing AE above. Since [l/ls(0)li is greatest when the number of unpaired electrons is largest we expect the isomeric shift to decrease in the order 6A . . lA and 5T2 . . 2T2. The s-electron density also depends markedly upon the environment of the Mossbauer nucleus (see Tables 3 and 4) and we can expect the effect of the a-induced polarisation of the s shells to be least for a symmetrical ground state.This is observed and we can therefore qualitatively represent the variation in isomeric shift of octahedral iron complexes as follows FeI" Few j o ; i Fe2+ FeII Few 2.4 The S/dEQ Correlation Diagram.-A diagram of 6 plotted against LIE for the same M6ssbauer nucleus has some interesting ,... *. U - Fe "I Fen Fe 2+ Fern Fe 3+ u- FIG. 3. ~/AEQ correlation diagram for a number of iron complexes. The circles indicate the approximate positions expected for iron complexes of octahedral symmetry. Brady Wigley and Duncan Rev. Pure Appl. Chem. (Australia) 1962,12,165. DUNCAN AND GOLDING M~SSBAUER STUDIES OF CHEMICAL BONDING 47 Fig. 3 shows the correlation diagram for a large number of iron complexes ; the small circles indicate the positions expected for the octahedral iron complexes.The areas indicating Fe3+ FerIr Fe2+ Fe" were obtained experi- mentally from results on about twenty different compounds of all types. With the aid of such a correlation diagram it is possible to assign the electronic configuration and to study the influence of different ligands on the nucleus under examination. 2.5 Temperature-dependence.-In a previous section we discussed the difference in Mossbauer spectra above and below the Curie temperature due to the change in the magnetic properties of the material. Below the Curie temperature an atom in a magnetically aligned environment usually shows hyperfine Zeeman splitting. The experimentally determined internal magnetic field (from the Zeeman splitting) in metals is found to be tem- perature-dependent ; this corresponds closely to the temperature-depen- dence of the ~ a g n e t i s a t i o n .~ ~ ~ ~ For there to be a change in the quadrupole splitting with temperature it is necessary to have an electronic excited state close to the electronic ground state. This has been suggested36 as an explanation of the marked temperature-dependence with Fe2+ salts such as Fe(NH4),(S0,),,6H,0. However in 3d iron complexes the first excited electronic state is fre- quently well above the ground electronic state and consequently a temper- ature-independent AE term is obtained. This is not the case with the 4f rare-earth complexes. Here spin-orbit coupling is very large and the weak crystal-field interactions produce low-lying excited states leading to tern- perature-dependent quadrupole splitting.MOssbauer3' observed such a temperature-dependent quadrupole splitting in thulium metal. 2.6 Other Correlations.-Any physical property dependent on the electronic or nuclear states will be related in some way to AEQ and 6. Two examples must suffice. The first is the linear relation between the magnetic susceptibility and dE over a wide range of values for Fe3+ Any deviation from the expected zero value of d EQ for a d5 Fe3+ ion must arise through an electric-field gradient at the nucleus due to the ligands. In such a case the magnetic-susceptibility variations in Fe3+ complexes must similarly depend upon the ligands. A second example39 is the linear relation between the proton magnetic resonance chemical shifts and the 57Fe isomeric shifts for several cyclo- pentadienyl iron complexes.Such correlations relate variations in the electronic ground and excited 36 Meyer-Schutzmeister Preston and Hanna Phys. Rev. 1961 122 1717. s6 DeBenedetti Lang and Ingails Proc. 2nd Mossbauer Conf. Paris Wiley New 37 Mossbauer Proc. 2nd Mossbauer Conf. Paris Wiley New York 1961. 38 Brady Duncan and Mok unpublished results. York 1961. Herber King and Werthcim Inorg. Chem. 1964 3 101. 48 QUARTERLY REVIEWS states from compound to compound. An interpretation is to be sought in the s-electron density and the electric-field gradients in the atom. Since Mossbauer spectra enable these two quantities to be determined un- equivocally at one place in the atom (the nucleus) the method illuminates in a fundamental way the interpretation of results determined by other methods.3. Practical Aspects In this section we summarise those aspects likely to concern the reader who is considering work of this kind Two practical aspects of importance are (a) the nature of the necessary equipment and (b) the number of suitable isotopes. 3.1 The Apparatus.-Spectra may be determined in a number of ways the cost depending on the degree of sophistication employed.34 Either scintillation or proportional counting methods may be used. The moving parts may be either electronically or mechanically driven. The latter is simpler but the former allows errors in the movement to be eliminated by feedback methods. Both require special construction. The electronic method normally requires a wave-form generator transducer (e.g.high- fidelity loud-speaker) to drive the source and associated components. The mechanical technique involves only workshop time and minor ex- penditure on materials but good machining is essential to avoid loss of resonance intensity caused by vibrations. Mossbauer spectra can be recorded in a variety of ways depending on the method used for driving the source (or absorber). There are two general methods. The spectrum can be determined point by point by moving the source at a constant velocity towards or away from the absorber. About ten minutes may be necessary to determine one point with sufficient accuracy and therefore about five hours for a complete spectrum. Each point may be recorded independently either manually or automatically by using a single scaling unit.The method is relatively cheap but is subject to error from electronic drift. A second more satisfactory arrangement is to drive the source with a constant-acceleration cam (ca. 1 rev./min.). The output froin the scintillation spectrometer is recorded against velocity. A convenient method is to employ a pulse-amplitude analyser with channel selection controlled by a potential related to the velocity at which the events are recorded. Anti-coincidence equipment to reject unwanted pulses may be useful. This reduces errors due to stray radiation background fluctuations etc. 3.2 Isotopes.-Even with 67Fe with which most work has so far been done many possible applications of the Mossbauer effect in chemistry remain to be studied. However there are a number of other isotopes which can be used; the situation is rather similar to that for nuclear magnetic resoname spectroscopy.About eighty isotopes which may be suitable have DUNCAN AND GOLDING MOSSBAUER STUDIES OF CHEMICAL BONDING 49 been li~ted,~,~O but not all have been shown experimentally to exhibit the Only l19Sn and 57Fe have been used for any systematic chemical work. In some cases it has been asserted that low temperatures are essen- TABLE 5 . Some suitable Mossbauer Decay Resonant nucleus 57Fe l19Sn 125Te 1291 lZ9Xe scheme energy (kev) 57Co-+67Fe 14.4 (270 day) 119Sn*+119Sn 23.8 (250 day) 129Te-1291 26.8 (70 min.) 1291,129xe 79 (1.6 x lo7 yr.) Mossbauer nuclei. Chemical features Source 5 7 c ~ in copper stainless steel. Absorbers numerous chemical compounds over a wide range of temperatures.Source in SnQ,. Absorbers numerous chemical compounds over a wide range of temperatures. Source 125Sb in copper. Absorbers MnTe CrTe a-TeO,. Source lZgTe in ZnTe. Absorbers iodides io- dates enriched with 1291. Both source and ab- sorber cooled in liquid nitrogen . Source in NaI NaIO,. Absorber clathrate compounds XeF, XeF,. Ref. 47 48 49 50 51 52 42,43 I 44 45 40 Frauenfelder “The Mossbauer Effect,” Benjamin New York 1962. 41 Wertheim Science 1964 144 253. 4a Hien Shapiro and Shpinel’ Soviet Phys. JETP 1962 15 489 (Zhur. eksp. teor. 43 Shikazono J. Phys. SOC. Japan 1963 18,925. 44 de Waard de Pasquali and Hafemeister Phys. Rev. Letters 1963 5 217. 4s de Waard Garrell and Hafemeister Phys. Rev. Letters 1962 3 59. p6 Jha Segnan and Lang Phys. Rev. 1962 128 11 60.47 Bryukhanov Delyagin Opalenko and Shpinel’ Soviet Phys. JETP 1963 16 310 (Zhur. eksp. teor. Fiz. 1962 43 432). Bryukhanov Gol’danskii Delyagin Korytko Makarov Suzdalev and Shpinel’ Soviet Phys. JETP 1963,16,321 (Zhur. eksp. teor. Fiz. 1962,43,448). 4s Aleksandrov Delyagin Mitrofanov Polak and Shpinel’ Soviet Phys. JETP 1963 16,879 (Zhur. eksp. teor. Fiz. 1962 43 1242). so Aleksevskii Hien Shapiro and Shpinel Soviet Phys. JETP 1963 16 559 (Zhur. eksp. teor. Fiz. 1962 43 790). 61 Bryukhanov Gol’danskii Delyagin Makarov and Shpinel’ Soviet Phys. JETP 1962 14,443 (Zhur. eksp. teor. Fiz. 1962,42 637). 62 Boyle Bunbury and Edwards Proc. Phys. Soc. 1962,79,416. 63 Shpinel’ Bryukhanov and Delyagin Soviet Phys. JETP 1962,14,1256 (Zhur. eksp. teor. Fiz. 1961 41 1767). Fiz. 1962 42 703).Perlow and Perlow Rev. Mod. Phys. 1964,36 353. 50 QUARTERLY REVIEWS Mossbauer Decay nucleus scheme 151EU 151Gd,151E~ (140 day) 161Dy 161Dy*+161Dy (7.2 day) (27 hr.) 166Er 166H0+166Er 197AU 197pt+f97AU (18 hr.) TABLE 5-continuqd Resonant Chemical features Ref. energy (kev) 54 55 I 21.7 Source in Nd203 Eu203. Absorber Eu203. 26 Source Gd,03. Absorbers Fe2Er Er 56a Absorber Dy,O,. 80.7 Source HoA1,. ErFe,Mn Er20,. Absorber Au Au in Fe. i'" 77 Source enriched Pt foil. 122 J tial for observing the effect but since the efficiency of recoilless productions and absorption of y-radiation depends on the chemical form of the host material this statement is not generally true. In Table 5 the relevant data are given for the principal isotopes with which the Mossbauer effect has been studied.3.3 Other Experimental Features.-An important feature is the pre- vention of loss in the resonant y-ray energy by nuclear recoil. This is usu- ally accomplished by incorporating the radioactive atom in an ionic lattice so that the whole of the source must recoil for each emission. It is however not satisfactory to choose just any ionic lattice for incorporating the radioactive material since atomic vibrations of the emitting atom which vary from one compound to another can change the y-ray energy sufficiently to preclude resonance. The more tightly bound the radio- active atom is (the higher the vibration frequency and the lower the vibra- tion amplitude) the greater the resonance intensity. Careful source pre- paration is therefore essential. Fortunately several methods for preparing satisfactory sources have already been given.34 The same considerations however also apply to the absorber.Very poor resonances invariably result from poor absorber preparations so that material which easily decomposes or which cannot be easily purified should not be used. Another way of reducing the effect of nuclear vibration is to lower the temperature. This may of course alter the chemical environment owing to phase changes and changes in the electronic ground state. But even if it does not 6 and LIE may be temperature-dependent. However these temperature-dependent variations are small and well-known so that lowering the temperature is a useful method of improving the detection of 64 Shirley Kaplan Grant and Keller Plzys. Rev. 1962 127 2097. 65 Delyagin Shpinel' and Bryukhanov Soviet Pliys.JETP 1962,14,959 (Zhur. eksp. 66 Sklyarevskii Sanioilov and Stepanov Soviet Phys. JETP 1963 16 1316 (Zhur. teor. Fiz. 1961 41 1347). eksp. teor. Fiz. 1961 40 1874). Cohen and Wernick Phys. Rev. 1964 134 B503. DUNCAN AND GOLDING MOSSBAUER STUDIES OF CHEMICAL BONDING 51 y-ray absorption. This is often done by using a foam-plastic vessel in which to keep the refrigerant. 3.4 Experimental Mossbauer Spectra.-The experimental features of a Mossbauer spectrum are quite simple. Figs. 4 and 5 show two typical Mossbauer spectra. The y-ray absorption intensity is recorded against the Doppler-shift velocity (cm./sec.). Since the Doppler-shift energy is Eov'/c (Section I) this can be converted into the usual energy units by remember- ing that for 57Fe 1 cm./sec.= 0.00388 cm.-l. The spectrum is recorded in a pulse-amplitude analyser until several-thousand y-ray quanta have been detected. To record a spectrum over a period of a few hours therefore requires a source of about 2 millicuries. FIG. 4. The Mossbauer spectrum for 57Fe in antiferromagnetic Fe203.24 The positions of the six hyperfine lines-intensity ratio 3 :2 1 1 :2 :3-depend on the magnetic-field and electric-field gradient interactions. The arrows indicate the positions of the six lines if the electric-field gradient interaction were zero. -0.4 -0-2 0 +o-2 0 4 Velocity (cm/sec) FIG. 5. The Mossbauer spectrum of iron(u) sulphate AEQ is the quadrupole splitting; 6 is the isomeric (or chemical) shift; and A and B refer to the energy of the stainless- steel single-line y-ray emission and the centre of the iron(I1) sulphate spectrum respect- ively.52 QUARTERLY REVIEWS The Mossbauer spectrum for 57Fe in antiferromagnetic Fe20324 (Fig. 4) shows the six hyperfine lines arising from the magnetic-field interaction (Section 2.1). When the effective magnetic field is zero only the quadrupole interaction is observed; this is shown in Fig. 5 the Mossbauer spectrum of iron(@ sulphate. The quadrupole splitting AE, is in this case 0.320 cm./sec. (= 0.00124 cm.-l). The isomeric shift 6 the difference between the energy of the stainless-steel single-line y-ray emission (A) and the centre of the iron@) sulphate spectrum (B). Here 6 = 0.131 cm./sec. (G 5-08 x cm.-l). The magnetic-field and quadrupole interactions and the isomeric shift can thus readily be evaluated from a Mossbauer spectrum.In general Mossbauer spectra are never more complicated than these unless two or more species are present to give overlapping spectra. 4. Chemical Applications In this Section we discuss some illustrative examples of typical chemical problems. We have made no attempt to discuss the large number of com- pounds which have been studied (see earlier review^).^,^^,^^ Table 6 gives some recent examples of the use of the Mossbauer effect. 4.1 Magaetic Fields in Alloys.-Included in Table 6 are several cases where chemical interest is centred on the source. This technique has been widely used in studying the magnetic fields of binary metallic compounds and alloys (Table 4). Both the magnitude and the sign of the internal magnetic field can readily be found in this way.The internal magnetic field at a nucleus may be either increased or decreased by an externally applied magnetic field. By convention the internal magnetic field in the first case is taken as negative and in the second case as positive. We have assumed here that the internal magnetic field is not affected appreciably by the domain magnetization. Nuclear magnetic resonance studies yield more accurate measurements of internal magnetic fields at nuclei but normally the resonance is so broad that it is difficult to detect without prior know- ledge of its position. 4.2 Structure of Compounds.-In the complex ferrocyanides Prussian Blue Turnbull's Blue and Berlin Green it has been that in all three cases the cation and the anion are in the oxidized and reduced states respectively and that the compound prepared by precipitation from iron(rr1) sulphate and potassium cyanoferrate(r1) is identical with that pre- pared from iron@) sulphate and potassium cyanoferrate(r1).In the SnX series of compounds a linear relationship between the isomeric shift and both the electronegativity of the X atom and the degree 57 Fluck Kerler and Neuwith Angew. Chern. 1963 2 277. 58 Duncan and Wigley J. 1963 1120. TABLE 6. Recent examples of the use of the Mossbauer efect in chemical work. Source 57Fe/57Co in a single crystal of NaI. 57Fe/57Co in silicon and germanium. 57Fe/57Co in stainleqs steel and l19Sn in SnO,. 57Fe/57Co in stainless steel. 57Fe/57Co in copper. 57Fe/57Co in metallic chro- mium. 57Fe/57Co in metallic chro- mium. 57Fe/57Co in metallic chro- mium. 57Fe/57Co in stainless steel.l19Sn in llSSn-enriched SnO,. Absorber Stainless steel. 57Fe-enriched K,[Fe(CN),] . FeSn as powder on beryllium disc. Oriented FeF,. Glasses of Na20,3SiO with Fe203 incorporated. Fe( PO3) cry st als. Ferrocene-type compounds. Fe(CO) and related com- pounds. K,FeO Single-crystals of white tin cut along various crystal planes. Type of work Change in dE observed for different orientations. Positive-hole vacancies and substitutional incorporation. No difference between n- and p-types. Asymmetric positions for FeO and Fe-1 in Ge lattice. Fe is electrically inactive. Internal magnetic field below Curie point measured and effect of this on l19Sn resonances determined Internal magnetic field in antiferromagnetic state measured. Magnetic hyperfine splitting in absence of external field resulting from long electron-relaxation time.Antiferromagnetic below 1 0 " ~ . Bonding of iron atom not affected by ring substitution. Results for Fe(CO) and Fe,(CO) agree with trigonal bipyramid and 333 structures respectively. Fe,(CO), probably is 3333 structure and is not trigonal as X-ray results suggest. Fe(CO),I is low spin. Data indicate complete covalent bonding between iron atom and n-electron distribution of cyclo-octatetraene ring system. Results interpreted in terms of d3s hybridisation. Large anisotropy studied for various orientations and temperature-dependence. Ref. 69 62 60 64 68 65 63 66 67 50 TABLE 6.-continued Source U9Sn in SnO,. l19Sn in SnO,. l19Sn in SnO,. 125Te/125Sb in copper or iron. 1311/131Xe in NaI. 1291/129Xe in NaI or Na12910, or 129~2.161Eu/151Gd in 151Eu-enriched Eu 203. 197A~/197Pt in 19 metals and semiconductors at 4 . 2 " ~ . } Absorber Type of work Ref. SnO, SnO Sn Sn(NO,),. 55 Tin-organic polymers. Investigation of tin-carbon bonding. 51 compounds. TeO, MnTe CrTe. Resonance intensity measurement and dependence of AE on temperature. (C,H,),SnX and related nEQ and 8 vary with electronegativity of X. 49 Determination of internal field and nuclear moment. 68a 131XeF 12%e clathrate. Study of Xe compounds such as XeO,. Eu(EtHSO,) nEQ suggests mixingof 5p56p1 (lo,) and 5p6 (lS,) states. 61 3 E Gold dEQ correlated with electronegativity differences be- 59 E tween host metal and gold. Barrett Grant Kaplan Keller and Shirley J. Chem. Phys. 1963 39 1035. 6o Nikolaev Shcherbina and Karchevskii Zhur. eksp. teor.Fiz. 1963 44 775. Judd Lovejoy and Shirley Phys. Rev. 1962 128 1733. 62 Noreni and Wertheim J. Phjx and Chem. Solids 1962 23 1 1 11. 63 Herber Kingston and Wertheim Inorg. Chem. 1963 2 153. 64 Wertheim Phys. Rev. 1961 121 63. 65 Wertheim and Herber J Chem. Phys. 1963 38 2106. 66 Wertheim and Herber J. Anzer. Chem. SOC. 1962 84 2274. 67 Wertheim and Herber J. Chem. Phys. 1962 36 2497. 6 8 ~ Shikazano J. Phys. SOC. Japan 1963 18 925. 60 Mullen Phys. Rev. 1963 131 1410; 1415. Kurkjian and Buchanan Phys. and Chem. Glasses 1964 5 63. DUNCAN AND GOLDING MOSSBAUER STUDIES OF CHEMICAL BONDING 55 of ionisation of the bond has been found.’O Such a graph gives insight into the type of bonding in similar tin compounds. Any quadrupole splitting observed in these compounds would indicate a deviation from tetrahedral symmetry.For instance the quadrupole splitting in SnF has been attri- buted71 to a polymeric structure in which each tin atom is bound to six fluorine atoms two of which have no additional bonds while four form bridge bonds between the tin atoms. 4.3 Gas-phase Adsorption and Surface Reactions.-Mossbauer spec- troscopy is also applicable to the study of solid-surface phenomena such as gas-phase adsorption and to surface reactions in liquid solutions. Little work of this type has so far been reported. The potentialitizs of the method can be illustrated by the adsorption of cobalt(r1) ion on precipitates of cobalt(r1) and iron(1r) o x a l a t e ~ . ~ ~ One would expect cobalt(I1) to be ad- sorbed on the surface sites of these precipitates in such a way that the en- vironment of the anions is asymmetric and quite different from that due to cations in the body of the solid.Experimentally however the shape of the Mossbauer spectrum using such a source with a stainless-steel absorber is identical within experimental error with that obtained with a copper- backed source and an iron@) oxalate absorber. It is also very similar to that obtained with a cobalt(r1) oxalate adsorbate; it is not affected by the length of time the precipitate is allowed to stand in contact with the active super- natant liquid; and is indistinguishable from spectra obtained when the precipitate is formed in the presence of radioactive material (it?. the 57Fe was formed by decay from the 5 7 C ~ in lattice sites). From these results two conclusions may be drawn.First the environments of iron atoms in cobalt(Ir) and iron(r1) oxalates are very similar. This implies that the crystal- line structures are similar which is not unreasonable in view of the similar ionic radii of the Co2+ and the Fez+ ions. Secondly the environment of surface-adsorbed ions is similar to that of ions within the lattice. 4.4 Single-crystal Studies.-The majority of Mossbauer spectra have been obtained from microcrystalline powders which give only averaged spectra. Consequently information is lost. By using a single crystal we may observe the y-ray absorption in different crystal orientations. It has been shown (Section 2) that in paramagnetic iron complexes the quadru- pole-split doublet in the y-ray absorption spectrum has an intensity ratio of 3(1 + cos28):(5 - 3cos28) where 8 is the angle between the electric- field gradient and the y-ray direction.Hence from the ratio of the in- tensities of the doublet lines the direction of the electric-field gradient in the single crystal can be determined. We have recently used this technique to determine the electric-field gradient in sodium nitroprusside single 70 Gol’danskii Atomic Energy Review vol. 1 No. 4 p. 3 International Atomic 71 Khaiduk see ref. 70. 72 Brady and Duncan J. 1964 653. 73 Duncan and Golding unpublished results. Energy Agency Vienna 1963. 56 QUARTERLY REVIEWS Single-crystal studies can sometimes readily reveal the presence of more than a single site in the lattice. For example Alff and We~theim,'~ using a single crystal of yttrium iron garnet have shown that there are three non- equivalent sites (one octahedral and two tetrahedral) for the 57Fe atoms in the structure.4.5 Electronic Configurations.-From the internal magnetic field or the isomeric shift 6 we can evaluate the s-electron density at the nucleus from the nucleus-electron interaction represented by the Fermi contact term in the spin Hamiltonian (eqn. 5). This term also accounts for the isotropic hyperfine interaction in electron spin resonance spectroscopy12 and the magnitudes of temperature-dependent shifts in nuclear magnetic resonance spectra of paramagnetic complexes.1o Such measurements are therefore important in order to test the validity of an electronic configura- tion for a molecule. For instance the nai've Aufbau principle implies a zero Fermi contact interaction. However we deduce from experiments that this is not the case.The Fermi term probably arises in three ways,4 namely (i) from mixing of excited electronic states containing unpaired s-electrons with the ground state (ii) by a spin-polarisation effect due to different spin-exchange interactions and (iii) by ligand-field mixing of the appropriate electronic configuration with the ground state. These important features of molecular electronic configuration can readily be investigated by means of Mossbauer spectroscopy. This new technique in chemistry thus provides ways in which basic ideas about molecular structure can be investigated and is a valuable extension to the general field of spectroscopy. This work is supported at the Victoria University of Wellington by the United States Air Force. '* Alff and Wertheim Phys. Rev. 1961 122 1414.

ISSN:0009-2681    

DOI:10.1039/QR9651900036

出版商:RSC    

年代:1965

数据来源: RSC

摘要:

THE STUDY OF COMPLEXED METAL IONS BY POLAROGRAPHIC METHODS By D. R. CROW (WEST HAM COLLEGE OF TECHNOLOGY LONDON) and J. V. WESTWOOD (SIR JOHN CASS COLLEGE LONDON) 1. Introduction THE polarographic reduction wave of a simple (aquo) metal ion is usually shifted in the direction of more-negative potential on addition of a com- plexing agent. Direct measurement of the shift in half-wave potential can serve for the determination of stability constants of complexes in solution provided that reactions at the dropping-mercury electrode occur reversibly. With suitable modifications however irreversible cases can be dealt with in many instances. Comparatively few systems are such that direct application of simpler theory serves for stability constant determination. In many instances reduction waves are both kinetically and diffusion controlled and the rates of dissociation of complex species control to a greater or lesser extent the shapes of the waves.Systems consisting of several complexes are encountered in which both reducible and non-reducible species occur in which equilibria between some species are less mobile than others. The overall kinetics of several such systems have been elucidated and the nature structure and behaviour of each species identified in addition to the calculation of their stability constants. From such applications the polarograhic method has been developed as a useful tool for the deter- mination of the structure of complexes. In the past stability constant data and little more resulted from the study of complex systems. While there is still a lack of such important data work in recent years has more constructively turned to the problem of determining the overall mechanism by which complexes of different known structures undergo reduction.Unknown structures may then be inferred from similar polarographic behaviour or confirmation may be given for structures already indicated by other techniques. 2. Stability Constant Determinations from Reversible Reductions (a) Formation of a Single Complex.-The Heyrovsky-Ilkovic equation1 expresses the half-wave potential (Ei) for the reduction of a metallic species in terms of the diffusion current (id) and the current(i) at any other point on the polarographic wave corresponding to the potential (Ed. e.) applied to the mercury drops. RT i &.e. = Ei - n~ In 1 J. Heyrovsky and D. Ilkovic Coll.Czech. Chem. Comm. 1935 7 198. 57 58 QUARTERLY REVIEWS The validity of this equation has received ample experimental verifica- t i ~ n . ~ ~ Provided that the reductions occur reversibly the E& value of a com- plexed species MXj will have a more-negative value than that of the “simple” (aquo) species M. A measure of this shift serves to determine both the co-ordination number and the stability constant of the complex. It can fairly simply be shown that the shift to a first approximation by ignoring activity coefficients may be expressed in the following relation- ship :4 in which (E& and (Ei) are the half-wave potentials of the simple and complexed species respectively j is the co-ordination number of the complex flj its stability constant and Cx the ligand concentration.Half-wave potentials of complexed metal ions shift with changing activity of the complexing ligand in accordance with Hence the number of ligands j bound in the complex is found from a plot of log, C against (E&c which in the present case should be linear. By the application of eqn. (2) Lingane4 showed the presence of the hydrogen plumbite ion in a strongly alkaline solution of lead hydroxide whose reversible reduction is represented by HPb02- + H20 + 2e + Pb(Hg) + 3 OH- (4) @) Formation of a Series of CompIexes with a Single Ligand Type.-In this category there are essentially two classes of systems viz (i) those in which each complex species exists only within a definite region of ligand concentration (i.e. two or more complexes with different co-ordination numbers are not present together) and (ii) systems which consist of a series of complexes in step-equilibrium (i.e.two or more complexes co-exist but different species predominate at particular ligand concentra- tions). (i) Occasionally a plot of logloCx against (E+) produces a segmented curve indicating the presence of a series of complexes whose stability constants and formulae may be found from the various segments. Such behaviour is shown for example in the ferro-ferri-~xalate,~~~ the zinc- ammonia,6 and cadmium-pyrazole systems. ’ It has been demonstrated a I. M. Koltlioff and J. J. Lingane Chem. Rev. 1939 24 1. J. Tomes Coll. Czech. Chem. Comm. 1937 9 150. J. J. Lingane Chem. Rev. 1941 29 1. M. von Stackelberg and H. von Freyhold Z. Elektrochem. 1940,46 120. R. Cernatescu I. Popescu A.Cracium M. Bostan and N. Iorga Studii si Cercetarj Sti. Chim. (Fil. h i ) 1958 9 1. 7 A. C. Andrews and J. K. Romary Znorg. Chem. 1963,2 1060. CROW AND WESTWOOD COMPLEXED METAL IONS 59 that for the segmentation of the curves to be sufficiently pronounced for the calculation of stability constant data the constants must differ by a power of ten or more. (ii) For a system of complexes in step-equilibrium the plot of log,,C against (E+)c is a continuous curve. The first serious attempt to consider the full implications of step-equilibria in the study of complex-formation by the polarographic method was made by DeFord and Hume8 who obtained the following relation between the change in half-wave potential and the free-ligand concentration [XI for a reversible metal deposition N [a = (Ed* - ( m c l Here IM and Ic are the diffusion-current constants for aquo and complex metal ions respectively the y’s are activity coefficients the P’s are stability constants (Po = 1 for the “zero” complex) and [XI = free-ligand concentration.The current-potential curve for such a deposition has been shown to be:g N RT i ~ nF nF id - i &i.e. = E0 - - In 2 &[X]i - (7) 0 The graphical method due to Ledenlo is then applied. If allmeasurements are made at the same ionic strength and the activity quotients dropped from eqn. (6) the right-hand side may be denoted by Fo[X] indicating that it is a function of free-ligand concentration and written as follows &[XI = P o + Pl[XI + P,[XI2 + * - * 3- P“X1N (8) A new function Fl[X] may then be defined by In a similar manner other functions may be derived giving finally * D.D. DeFord and D. N. Hume J. Amer. Chem. Soc. 1951,73,5321. P. Kivalo and H. A. Laitinen J. Amer. Chem. Soc. 1955 77 5205. lo I. Leden 2. phys. Chem. 1941,188 160. 60 QUARTERLY REVIEWS From eqn. (9) a plot of Fl[X] against [XI gives a curve having a limiting slope of p2 at [XI = 0 and an intercept of pl. Such plots are made for each function until all the complex species are accounted for the penulti- 1 that for the highest com- axis. Fig. 1 is a schematic mate graph being linear with positive slope and plex a straight line parallel to the concentration r 1 I I BI - FIG. 1. Schematic plots of F[X] functions for a system of three complex species in step-equilibrium. representation of a set of graphs expected for such a system with three complex species formed.In the original DeFord-Hume derivation,8 (E#) was designated (E+O) to indicate that it was the half-wave potential of the simple ion when its activity was unity. There is then little justifica- tion for assuming that the first term in eqn. (6) is unity it is in fact p0/.yM. As used above (E& refers to the value obtained in a medium of the same ionic strength as that used in the measurements on the com- plexed cation. For a particular system the ligand number i is definedll by so that a plot of log,J,[X] against loglO[x] gives a curve whose slope at any point gives the value of ii corresponding to a particular value of [XI. i then represents the average composition MX, of the species present in solution. On increasing [XI the composition will approach that of the highest complex MXN and eqn.( 5 ) may be expressed in the form Eqn. (12) is identical with eqn. (2) under these limitingconditions if it is assumed that I = Ic and [XI = Cx. The earliest practical applications of the theoretical work of DeFord and Hume were to the cadmium and l1 H. Irving “Advances in Polarography,” Pergamon London 1960 vol. 1 p. 49. CROW AND WESTWOOD COMPLEXED METAL IONS 61 zinc thiocyanate complexes. Hume et a2.l2 determined the half-wave potentials of the cadmium ion in potassium nitrate-thiocyanate mixtures over a thiocyanate concentration range 0-1-2-0 M at a constant ionic strength of 2 M. The above treatment revealed the presence of four com- plex species CdSCN+ Cd(SCN), Cd(SCN), and Cd(SCN),2- with consecutive stability constants 11 56 6 and 60 respectively.Over this thiocyanate concentration range the half-wave potential was observed to change from -0.5724 v to -0.6646 v [against standard calomel electrode (S.C.E.)] with a corresponding decrease in the diffusion current from 7.56 PA to 7-03 PA. Such small shifts in Ei values demand very careful measurement and this can only satisfactorily be done by the use of manual equipment. In the case of the zinc complexes the overall shift was from -0.9977 v to -1.079 v (against S.C.E.),13 so small that earlier investigators had reported the absence of c~mplex-formation.~~ A recent study of the cadmium-azide system15 revealed the presence of the five complex species GIN,+ Cd(N3)2 Cd(N,),- Cd(N,),,- and Cd(N3)2-. (c) Formation of Mixed-ligand Complexes.-Since the above early applications many other systems have been studied.A notable contribu- tion which seems to have aroused little interest is the extension of the DeFord-Hume approach by Schaap and McMasterP to deal with mixed- ligand systems. For a complexing reaction of the type M + iX +jY + . . . . = MXtYi.. . . (1 3) in which i j . . . . are stoicheiometry numbers and X Y . . . . are different ligands the DeFord-Hume expression for the Fo[X] function may be extended to give a new function Fo0 .... [X,Y . . . .I given by N AEh + log - M As before each term in eqn. (14a) is determinable except for y,,which is included in the resultant equilibrium constants. For a total of three bound ligands of the type X and Y factorisation of the Fo0 function leads to I;~o[XYYI = (180 P01fyI P0zI?12 1803[Y13) [XI0 (810 IBIIIYI P12[YI2IEXI 4- ( 8 2 0 + /%i[Y]>[Xl2 (15) (16) $- 1 P 3 o ) [XI3 or&,IX,Yl = A + B P I + C[X12 + D[XI3 la D.N. Hume D. D. DeFord and G. C. B. Cave J. Amer. Chem. SOC. 1951 73 5323. l3 R. E. Frank and D. N. Hume J. Amer. Chem. SOC. 1953 75 1736. P. R. Stout and J. Levy Coll. Czech. Chem. Comm. 1938 10 136. l6 P. Senise and E. F. de Almeida Neves J. Amer. Chem. Soc. 1961,83,4146. l6 W. B. Schaap and D. L. McMasters J. Amer. Chem. SOC. 1961 83,4699. 62 QUARTERLY REVIEWS where for a given w] A By C and D are constants. The original graphical solution may be applied to the Foo data if the activity of one of the ligands is held constant while that of the other is varied. For the copper- and cadmium-ethylenediamine-oxalate systems the oxalate concentration was held constant (at several fixed values) while that of ethylenediamine was varied.Thus [XI = [en] and [Y] = [ox]. For the Cd-en-ox system in which possible mixed complexes are Cd(en)(ox) Cd(en),(ox) and Cd(en)(ox),2- values of A and D were known from studies of the simple Cd-en and Cd-ox systems. B was obtained graphically from the Flo function defined by Foo - I;;o = [+] = B 4- c[en] + D[enI2 by plotting Flo against [en]. Similarly C is given by the Fzo function With a knowledge of C the mixed-complex stability constant ps1 may be calculated but in order to determine isll and isl2 B must be evaluated for at least two different oxalate concentrations. 3. Stability Constant Data from Irreversible Waves There are two essential approaches to the determination of stability constants from irreversible waves.These involve the use on the one hand of diffusion-current measurements and of half-wave-potential data on the other. In the majority of cases a process of competition for a ligand by the metal studied and an “indicator ion” is used. (a) The Use of Current Measurements.-In all the relations so far given it is usually assumed that the diffusion coefficients of the various species in solution do not differ to any great extent from one another and that the limiting current is therefore independent of ligand concentra- tion. Should there be a measurable difference between the diffusion co- efficients of a metal M and its complex MX the stability constant of the latter species may be determined by observing the change of diffusion current with ligand concentrati~nl~’~~ and applying the relation19 where DM and DMx are the diffusion coefficients of the free and com- plexed metal ions respectively and D is the observed mean coefficient in a solution containing the two species.Eqn. (19) can only be used for systems containing a complex with one bound ligand but since no poten- l7 V. KaCena and L. MatouSek Coll. Czech. Chem. Comm. 1953 18 294. l8 Z . Zabransky Coll. Czech. Chem. Comm. 1959 24 3075. lS J. Koryta “Progress in Polarography,” ed. P. Zuman Interscience New York 1962 vol. 1 p. 291. CROW AND WESTWOOD COMPLEXED METAL IONS 63 tial measurements are needed it may be applied to irreversible processes. Use of the method assumes a rapid attainment of equilibrium between the metal ion and the complex. In the case of very stable complexes for which completely non-labile equilibria may be assumed current measurements may also serve to pro- vide stability constant data by use of a method of competitive complex- formation largely developed by Schwarzenbach and his co-workers.20-22 Suppose that a metal complex MX is irreversibly reduced or is even electro- inactive at the dropping-mercury electrode.In order that the stability constant of MX may be determined it is necessary to have access to a complex NX whose stability constant is known and is of the same order as that of MX. The wave for uncomplexed N must be reversible occur at a more positive potential than that of M and be undetectable in the presence of NX when N and X are present together in equivalent concen- trations. Briefly the experimental procedure is as follows polarograms are obtained for N in both the presence and absence of X.A measured quantity of M is now added which competes for the ligand X some of which it abstracts from the previously formed NX finally setting up the equilibrium By this action ions of N are liberated and reduction waves are observed for both N and NX whose heights are directly proportional to the concentrations (Fig. 2). By observing the above conditions waves for M and X do not interfere; that of MX might well appear after that of hydrogen. The equilibrium constant for reaction (20) is given by M + N X + M X + N (20) Hence when KNX is known KMx is determinable. This technique has been used by Schwarzenbach and S a n d e ~ a ~ ~ in studies of vanadium complexes with ethyleiiediaminetetra-acetic acid (E.D.T.A.) using copper as the indicator ion N MX being NaJOY and NX Na,CuY.Many metals have been employed as the auxiliary cation in this method e.g. manganese zinc cadmium mercury copper and iron in the deter- mination of stability constants of aminopolycarboxylate complexes of many metal ions including the lanthanide~.~~-~~ 2o G. Schwarzenbach and H. Ackermann Helv. Chim. Acta. 1952,35,485. z1 G. Schwarzenbach R. Gut and G. Anderegg Helv. Chim. Acta. 1954 37 937. 22 K. Bril and P. Krumholz J. Phys. Chem. 1953 57 874. 23 G. Schwarzenbach and J. Sandera Helv. Chim. Acta. 1953 36 1089. 24 L. Holleck and G. Liebold Naturwiss 1957 22 582. a5 D. M. H. Kern J. Amer. Chem. SOC. 1959 81 1563. 26 F. H. Spedding J. E. Powell and E. J. Wheelwright J. Amer. Chem. SOC. 1956 78. 34.. - I - 27 G. Schwarzenbach and R. Gut Helv. Chim. Acta. 1956,39 1589. E. J. Wheelwright F. H. Spedding and G. Schwarzenbach J. Amer. Chern. Sac. 1953,75,4196. 64 QUARTERLY REVIEWS t FIG. 2. (a) Polarogram of metal ion N. (6) Polarogram of complex-ion NX. (c) Super- position of wave due to N upon that of NX on addition of metal ion M. (b) The Use of Potential Data.-A method due to S~brahrnanya~~ utilises a modification of the treatment of Lingane by Tamamushi and Tanake30 for an irreversible process i.e. (22) - j x 2.303RT - - A E d log c x an F By using the modified Heyrovsky-Ilkovic equation for an irreversible reduction 2RT anF i.e. Es - Ep = - . In 3 from which an was evaluated. Thus j was solved and the dissociation constant Kc deduced from the expression RT anF an F (Et) - (E& = - In Kc --lEln Cx R.S. Subrahmanya “Advances in Polarography,” Pergamon London 1960 vol. 2 p. 674. a. R. Tamamushi and N. Tanaka Bull. Chem. SOC. Japan 1949 22 227. CROW AND WESTWOOD COMPLEXED METAL IONS 65 The method has been applied to the study of the mono- di- and tri- ethanolamines of iron cadmium nickel cobalt copper lead and zinc at 30” in alkaline media. A few of the mono- and di-ethanolamine compounds are reversible but the triethanolamine complexes are invariably irrevers- ible. In addition at higher pH values OH- NH, and CO2- tend to enter the complex and by variation of the concentration of these species with constant amount of complexing agent in the base solution some of these additional species have been identified and their dissociation con- stants calculated.However the success of the method relies upon the reversibility of the simple ion in eqn. (24) and conditions giving a constant value of a so that it was inapplicable to cobalt and nickel although the formulae of the complexes including the mixed-ligand complexes were deduced. A further technique based on theoretical suggestions of Ringbom and E r i k ~ s o n ~ ~ ~ ~ also uses an indicator ion to compete with the ion studied for the complexing ligand. The method can be used in principle at least for studying systems containing a single complex or a series of complexes in mobile equilibrium which are electro-inactive or which give irreversible waves. If the indicator metal ion N is present in solution with an excess of ligand addition of ions M will decrease the free-ligand con- centration and give a consequent shift of the wave for the N-X system to more-positive values.It is necessary that M should react very rapidly with the ligand and that the complex equilibrium is established almost in- stantaneously. That the latter may not occur is a weak feature of the method A preliminary experiment is performed in which the shift in half-wave potential for the system NX is determined with increasing free-ligand concentration. The position of E+ for the system NX when M has been added then gives directly the free-ligand concentration from the preliminary calibration. The ligand number for the system MX is given by at the half-wave p~tential,,~ where Z‘ is the ligand number of the system NX [XI the free-ligand concentration Cx the total ligand concentra- tion CN the concentration of N and CM the concentration of M.If the activity coefficients are neglected the DeFord-Hume Fl function is expressed by N Fl[X] = KI 4- &D(] -l- &[XI2 -k . . . = z&[x]’-’ (27) 1 A. Ringbom and L. Eriksson Acta. Chem. Scand. 1953,7 1105. 8a L. Eriksson. Acra. Chem. Scand. 1953 7 1146. s3 F. J. Rossotti and H. Rossotti “The Determination of Stability Constants,” McGraw-Hill New York 1961 ch. 8 p. 185. 66 QUARTERLY REVIEWS It was shown by Fronaeou~~~ that N Then the graph of Fl[X] against [XI gives Kl as intercept and K2 as limiting slope. The process is continued up to FN. In this way Zabranskyl* determined the stability constants of the sodium and lithium E.D.T.A. complexes by using thallium as the indicator metal. Plumbic lead has also been used as the auxiliary cation for the determination of the stability constants of the chloro-complexes of nickel and zinc.35 The tedious nature of the technique when a series of complexes is formed and the slow attainment of equilibria in many cases may ac- count for the somewhat limited application and exploitation.4. Limitations of the Graphical Method Graphical solutions of the F[X] functions involve cumulative errors and this is reflected in the increased scattering of points in the graphs for higher complexes. This becomes even more apparent in the case of mixed-ligand complex-formation. Some attempt has been made for example by Irving,36 to use algebraic solutions for the various p’s. If more simultaneous equations of type (8) than there are unknowns can be set up from the polarographic data a least-squares treatment can be employed to find the best set of values.The ultimate equations in the DeFord-Hume and Eriksson techniques possess properties which allow of their being treated by the relaxation method. Examples of the use of the method with data obtained by using the above techniques are given in an excellent Paper by Watkins and Jones.37 Although the preceding refinements are of great importance it should be borne in mind that much improved data can be obtained by correct control of experimental conditions. Approximations valid for some sets of conditions do not hold in others. For example in the original treatment of the Cd-SCN system the total ligand concentration was used as an approximation for that of the free ligand (in terms of which the Leden functions are expressed).In this case the assumption was valid since the thiocyanate concentration was so large compared with those of the com- plexes that in the most dilute solutions with respect to the ligand the 84 S. Fronaeous Acta. Chem. Scand. 1950 4 72. a6 B. Kivalo and R. Luoto Suomen Kern. 1957 30B 163. 36 H. Irving ref. 11 p. 52. 87 K. 0. Watkins and M. M. Jones J. Znorg. Nuclear Chem. 1961,16,187. CROW AND WESTWOOD COMPLEXED METAL IONS 67 greatest error introduced was no more than 0.5 per cent. In cases where this assumption is no longer valid the ligand number n must first be found assuming at this stage that [XI = Cx. Then true (or truer) values of [XI may be calculated by substitution into the relation The fraction IM/Ic [see eqn. ( 5 ) ] should be included in the calculations since although small its neglect produces a significant positive error in the final consecutive stability constants.Many workers have ignored this fraction in their studies. Above all temperature and ionic strength must be maintained strictly constant over the entire ligand-concentration range. Any effect causing a potential shift which can be superimposed on that due to complex-forma- tion must be rigorously excluded. 5. Structural and Kinetic Factors affecting Reduction The overall redox process occurring at the electrode and in its immediate vicinity may be represented diagrammatically (Fig. 3) division into the stages being quite Elect surfa I Structural changes I I influence giving I under electrode I form capable of I ' Electron direct reaction transfer I with electrode 7- I - I+- I - I Structural changes I in primary products a c Edge Dde x dou b '3 Structural changes before entering double layer ___.I Chemical 1 changes of products >f electrode 3 layer Depolarizing particles diffuse in from bulk solution t -+ Products diffuse out t o bulk solution Electrode process -+ I I I+- I I=+ overall redox process - I (a) Structural Factors.-Both the mechanism and rate of the overall electrode process depend on the energy and localization of the lowest unoccupied (or singly occupied) orbital on the reducible species. It is into such orbitals that the electrons provided at the electrode in a reduc- A. A. Vlcek Progr. Org. Chem. 1963,5,216. 68 QUARTERLY REVIEWS tion process are re~eived.~*,~~ Should the depolarizing particle have a high electron affinity direct transfer of electrons to these vacant orbitals may take place.If such a condition does not hold the electronic energy of the complex may change in such a manner that direct reaction with the electrode is made possible.41 The energy necessary to produce this change constitutes an important and sometimes the major part of the activation energy of the electrode process. Configurational changes occurring im- mediately after the electron transfer cannot be directly determined and have to be inferred from the structures of secondary products derived from them.41,42 In attempting to correlate the structure of complexes with polaro- graphic behaviour recent studies have considered cases that reluctantly undergo substitution reactions so that the structure in solution may be assumed to be little different from that in the solid state.The most useful complexes in this respect have proved to be those of trivalent cobalt and chromium. Changes such as aquation which may occur in solution can in fact be of more help than hindrance since they usually take place to a sufficient extent to allow the change in morphology of the waves with time to be followed. Recent studies by V 1 ~ e k ~ ~ s ~ ~ have shown important correlations be- tween polarographic and spectroscopic behaviour. The energy of the “reactive” or “transition” state (capable of taking part in the electron transferences) depends on the energy differences between the ground and excited states of the central metal ion. Thus the energy depends on the ligand-field strength of the complex and if this is too large the complex may well be non-reducible.Any effect which decreases the energy difference leads to easier reduction. Vlcek’s studies involved substitution in octa- hedral cobalt(II1) complexes of the type COX to form CoX,Y. In many cases a Cox,-type complex is non-reducible whereas a substituted form may be reducible owing to the splitting of the e and tzg levels caused by the substituent Y. Should both forms of the complex be reducible the substituted form has the more-positive half-wave potential. The larger the separation of the ligands X and Y in the Spectrochemical Series the larger the potential shift. Similar trends are found for the complexes of chromium(II1) and rhodium(II1). (b) Distinction between Isomeric Species.-A study of cobaltammine isomers by Willis Friend and Mel10r~~ showed that polarographic half- wave potentials may sometimes be used to distinguish between the two structural types in solution.Since this work several studies of both A. A. Vlcek Coll. Czech. Chem. Comm. 1955,20,894. 40 A. A. Vlcek Nature 1956 177 1043. 41 A. A Vlcek Coll. Czech. Chem. Comm. 1957 22,948. 4 2 A. A. Vlcek Coll. Czech. Chem. Comm. 1957,22 1736. d3 A. A. Vlcek Discuss. Faraday SOC. 1958,26 164. 4 4 A. A. Vlcek Coll. Czech. Chem. Comm. 1959 24 181. 46 J. B. Willis J. A. Friend and D. P. Mellor. J. Amer. Chem. SOC. 1945 67 1680, CROW AND WESTWOOD COMPLEXED METAL IONS 69 octahedral and planar isomeric species have been carried out. Holtzclaw and sheet^,^,,^ found that in six-co-ordinated complexes of cobalt(m) containing two negative groups the trans-isomer was reduced at a more- negative potential than was the cis-form.For octahedral cobalt complexes the reductions proceed irreversibly in two main stages viz. cobalt(m)+cobalt(iI) and cobalt(II)-+cobalt. However the first stage cobalt(In)+cobalt(II) is in many cases repre- sented by a doublet wave and in others by a single wave. For example in the case of the isomers of [Co(NH,>,(NO2),]+ a single wave is obtained for the cobalt(rI1) to cobalt(I1) step with Ei values of -0-05 and -0.21 v (against S.C.E.) for the cis- and trans-forms respectively. The same relationship between Ei values and structure occurs with the first waves of the doublets as shown in Table 1. TABLE 1. Comparison of E+ vaIues for cis and trans cobalt(n1) isomers containing two negative groups.47 Complex Reduction cobalt(m)-+cobalt(rr) First wave Second wave -(Ei)i (v) (w.S.C.E.) - ( I 3 2 (v) (w.S.C.E.) [Co(en)2(NO,) I' cis 0.24 cis 0.41 trans 0.27 trans 0.40 CCo(en),(NCS)(No& I+ cis 0.04 cis 0.38 trans 0.12 trans 0.36 The second wave which in each case appears at about -0.4 v may correspond to the reduction of an aquated form of the parent complex the reduction of the parent complex itself being represented by the first wave of the doublet.Slight discrepancies between half-wave-potential values for the second waves in Table 1 would tend to suggest that these correspond to the reduction of different intermediate forms. The aquated species may be a hydroxo-complex of some A study of similar complexes with less than two negative groups was also carried out by the above workers and Ei values are given in Table 2 for two representative pairs.TABLE 2. Comparison of Ei values for cis and trans cobalt(1n) isomers with one negative group.Q7 Complex Reduction cobalt (111)-+co balt (11) First wave Second wave -(Ei)1 v (v3.S.C.E.) -(E+)2 v (v3.S.C.E.) [Co(en),NO2NH3I2+ cis 0.21 cis 0-40 trans 0.20 trans 0.40 [ CO(~~),NH,NCS]~+ cis 0.13 cis 0.39 trans 0.10 trans 0.39 p* H. F. Holtzclaw jun. J. Amer. Chem. SOC. 1951 73 1821. 47 H. F. Holtzclaw jun. and D. P. Sheetz J . Amer. Chem. SOC. 1953,75,3053. 70 QUARTERLY REVIEWS In their original publication the authors stated that in octahedral com- plexes containing only one or no negative groups there was no apparent difference between the polarographic behaviour of isomeric species.However as has been the data tend to suggest that slightly easier reduction of the trans-isomer occurs in such cases. of cis- and tvans-[Rh(en),Cl,]+ have shown that the half-wave potential of the cis-isomer is considerably more-negative than that of the trans-form. This is in contradistinction to the case of cobalt(m) complexes of similar type. (See Figs. 4 and 5 for polarograms of the two Recent FIG. 4. Polavograms of trans (n and cis (11) [Co(en),(NO&]+ (ca. 2.5 X M) in 0.1 M-NaClO,. Both waves start at 0.0 v. FIG. 5. Polavograms oftrans (I) and cis (TI) [Rh(en),Cl,]+ (ca. 2-3 x M) in 0 . 1 ~ - cases.) In our view it seems reasonable to explain the effect in terms of reduction occurring on different sides of the electrocapillary maximum for the cobalt and rhodium cases.In view of the greater internal dipole which exists within the cis-isomer of an octahedral complex containing two negative groups Holtzclawso suggested that in the absence of a supporting electrolyte this isomer on account of its correspondingly greater orientation in the unsymmetrical field around the dropping-mercury electrode should migrate to this electrode at a rate different from that of the trans-form. Investigations of NaC10,. Wave I starts at 0.3 v; wave I1 at 0.5 v. 48 J. R. Hall and R. A. Plowman Austral. J. Chem. 1956,9 14. 49 D. R. Crow and J. V. Westwood to be published. 6o H. F. Holtzclaw jun. J. Phys. Chem. 1955 59 300. CROW AND WESTWOOD COMPLEXED METAL IONS 71 various pairs of isomers in solution under these conditions showed that the different migration effects were not reliable as a means of distinguishing between the two structures.Half-wave-potential data on the other hand have found use in the identification of the different ~ p e c i e s . ~ ~ ~ ~ Similar studies have been carried out on the four-co-ordinated complexes of platinum and p a l l a d i ~ m . ~ ~ ~ ~ Platinum(r1)-tetra-amine ions in which the ligands are ammonia methylamine dimethylamine ethylenediamine pyridine aniline or combinations of these show a polarographic distinc- tion between cis- and trans-isomers. Trans-forms undergo easier reduction than do the cis-forms suggesting the greter thermodynamic stability of the latter. Chakravarty and Bane~jea~~ observed that for platinum(I1) and palladium(@ complexes containing two negative groups there is a signific- ant difference (of the order of 60 mv or more) in the E+ values of the isomeric forms the cis- now being reduced at a more-positive potential than is the trans-form.The general behaviour of such complexes is very similar to that of six-co-ordinated cobalt(m) complexes. For diaquo- and chloroaquo-complexes Ei values are almost identical. A striking difference between the planar and octahedrally co-ordinated structures is that for the former a definite difference between the behaviour of cis- and trans- forms is observed even when all groups are neutral. (c) Kinetic Factors.-Very often the rate of dissociation of a complex as well as the rate of diffusion controls the limiting current. It has proved possible to determine stability constants from the half-wave potentials and kinetic limiting currents obtained from dissociation-rate-controlled waves.The half-wave potential of the kinetic wave is less negative than that of the hypothetical diffusion-controlled wave and the difference can be used to compute consecutive stability constants in the normal way provided that the dissociation reaction is followed by a reversible dis- charge process. The relation for a diffusion-controlled deposition [see eqn. (7)] has been modified by K ~ r y t a ~ * - ~ ~ and Matsuda and Ayabe5’ to 0 Here i k replaces id of eqn. (7) and a new term is added. This in effect “corrects” the half-wave potential of the kinetic wave for the slowness of dissociation relative to the diffusion rate of a particular complex. Then 61 Z. E. Gol’braikh Zhur. neorg. Khim. 1956,1 1739. s3 B. Chakravarty and D.Banerjea J. Inorg. NucZear Chem. 1961,16 288. 64 J. Koryta Coll. Czech. Chem. Comm. 1958 23 1408. 65 J. Koryta Coll. Czech. Chem. Comm. 1959 24 2903. s6 J. Koryta Electrochim. Acta 1959 1 26. 67 H. Matsuda and Y. Ayabe Bull. Chem. SOC. Japan 1956,29 134. E. A. Maksimyuk and G. S. Ginzburg Doklady Akad. Nauk S.S.S.R. 1959 124 1069. 72 QUARTERLY REVIEWS and RT id + - I n nF i k (33) The method involves an estimated id value based on a reasonable value for D and a knowledge of n. These equations have found important uses for the determination of stability constant data for several systems. After “correcting” for the half-wave potential the procedure follows the DeFord-Hume graphical method.55p58p59 It is rare especially if faced with several step-wise equilibria to be able to know precisely the nature of the species present in solution.Not only are there often many species but added complications may arise due to binuclear complex-formation and also the low mobility of equilibrium between some species in the step complexes. Further not all the com- plexes may be electro-active at the mercury electrode. In some cases it has proved possible to determine both the chemical reaction controlling the overall rate and its rate constant. KorytaS0 studied the cadmium- cyanide system ([CN] = 0-005-0-1 M) and obtained a limiting kinetic current ik related to id the limiting (diffusion) current for rapid dis- sociation by use of the expression. = constant x (p - N - 8)ln[X] (34) where p and N represent the composition of the complex whose dissocia- tion is rate-determining and that of the highest complex present respect- ively.Experimental determination of the quotient d{ In [ik/(id - ik)]}/ d{ln[X]} yields a value for p when N is known. In the system quoted N = 4 and the quotient was found to have the value -3/2. Hence p = 3 and the reaction is rate-controlling. Should there be in a mobile system of complexes a species whose reduction (electrode reaction proper) controls the overall rate the com- position of this species may be found by a similar treatment. If p again represents the composition of the unique species and r p the rate constant of its reduction process the current relationship is Cd(CN),- = Cd(CN) + CN- (35) i id - i - . - 0.886 rD t ) D-5 ( k ~ . . . . kp+l.[X]N-p)-l (36) J. Koryta Coll. Czech. Chem. Comm. 1959 24,3057.69 D. Konrad and A. A. Vlcek Cull. Czech. Chem. Comm. 1963,245,808. 6o J. Koryta 2. Efektrochem. 1957,61,423. CROW AND WESTWOOD COMPLEXED METAL IONS 73 where t and D have the usual significance and the k’s are stability con- stants. Again p is found from the change in current with ligand concen- tration. In cases of more-complex behaviour both equations above have to be combined to take account of the two effects. 6. Solvent Variables In studies of complex-formation which involve measurements of half- wave-potential shifts it is necessary that care be taken to ensure that the observed shifts are due to complex-formation-especially that involving the required ligand-without interference arising from other ligands. It has already been shown that the nature of the complexes present in solution can differ widely with changing concentrations of the complexing ligand.If indifferent electrolytes with good co-ordinating ability are used these can have a pronounced effect on both half-wave potentials and diffusion currents. For example HoltzclaW46 investigated the behaviour of cis- and trans-dinitrotetramminecobalt(1ir) chloride with increasing concentrations of chloride tartrate and citrate and Laitinen et carried out similar studies on hexamminecobaltic chloride. Half-wave potentials were shifted in the negative-potential direction and diffusion-current constants were at the same time reduced. Such behaviour is attributed to “supercomplex” formation due to clustering of base electrolyte anions by ion-dipole and electrostatic attraction about the central complex.The formation of supercomplexes is closely allied with the phenomenon of ion-pairing the nature of which has been largely clarified by the work of BjerrumGa and Fuoss and K r a u ~ . ~ ~ Tur’yan and Bondarenkoe4 studied the effect of non-aqueous solvents on the polarographic behaviour of many complexes. The main feature of this work was the use of various concentrations of methanol or ethanol in water. The dielectric constant was found to have a pronounced effect on the stability of cadmium thiocyanate complexes; the stability con- stants varied inversely as the dielectric constant. In such mixed-solvent systems lower members of the Cd-SCN series of complexes are formed preferentially with a lower concentration of higher complexes and a general increase in stability with increasing coiicentration of non-aqueous solvent.Solutions of ethanol 2-methoxymethanol and dioxan in water have been used as polarographic solvents for copper chelates of 1,3-dike- tonesG5 and for copper and cadmium complexes with thiourea and its homologues. 66 Nightingale and HoltzclawG5 derived the expression 61 H. A. Laitinen J. C. Bailar H. F. Holtzclaw jun. and J. V. Quagliano J. Amer. Chem. SOC. 1948 70 2999. 62 J. Bjerrum Kgl. danske Videnskab. Selskab. Mat.-fys. Medd. 1926 7 No. 9. 83 R. M. Fuoss and C. A. Kraus J. Amer. Chem. SOC. 1933,55,1019,2387. 64 Ya. 1. Tur’yan and N. I. Bondarenko Zhur. neorg. Khim. 1959,4,1070. 66 E. R. Nightingale and H. F. Holtzclaw jun. J. Amer. Chem. Soc. 1959,81 3523. 66 T. J. Lane J. W. Thompson and J. A. Ryan J. Amer. Chem. SOC. 1959,81,3569. 74 QUARTERLY REVIEWS dE+ = constant x A k) (37) relating the half-wave-potential change and the corresponding change in dielectric constant E .Experimentally the value of the constant was found to be -3.5 in fair agreement with the calculated value of -4.09. The same workers investigated the effect of viscosity changes on the reduction of the ketone chelates and found that the Stokes-Einstein relation was in general obeyed. Values of diffusion coefficients needed for computation of the Stokes-Einstein product DT were obtained from the Lingane- Loveridge m~dification~~ of the Ilkovic equation which had not been rigorously tested for non-aqueous-solvent systems until this study. In a more recent study the effects of solvent isotopes have been ex- amined. Light and heavy water were used as solvents for the polarographic determination of stability constants of cadmium and copper oxalate complexes.6s The constants were found to be greater in heavy water than in the more-strongly-solvating light water.Increase in the ionic strength of an electrolytic solution shifts the half- wave potentials to more-negative values. In using the DeFord-Hume method activity coefficients are assumed to remain constant and inde- pendent of the concentration of the complexing agent by holding the ionic strength at a constant value. This assumption is not always justifiable in cases where concentrated solutions of mixed electrolytes are used. The polarographic method indeed has been applied to the determination of formation constants in LiN03-KN03 melts at 180°.69 In this way the chloro-complexes of nickel cadmium and lead were studied by the DeFord-Hume method.A similar application involved the formation of the species AgCI AgCI,- and Ag,C1+ in molten KN03.70 7. Thermodynamic Quantities Evaluation of AGO AHo and ASo is in principle possible from measurements of the formation constants at various temperatures al- though relatively few of such studies have been made polarographically. Earlier work on the complexes of nickel and copper with glycine and valine over the range 25-40' gave results in reasonable agreement with those obtained from potentiometric studies. 71 The AHo values varied from -14.0 to -21-0 kcal. but the ASo values varied considerably with both positive and negative results. A more recent study of cadmium-pyrazole complexes7 confirmed the presence of 1 1 1 :2 and 1 3 meta1:complex 67 J.J. Lingane and B. A. Loveridge J. Amer. Chem. SOC. 1950 72 438. 68 D. L. McMasters J. C. Raimondo L. H. Jones R. P. Lindley and E. W. Zelt- 6 9 J. H. Christie and R. A. Osteryoung J. Amer. Chem. SOC. 1960 82 1841. 'O J. Braunstein M. Blander and R. M. Lindgren J. Amer. Chem. SOC. 1962 84 mann J. Phys. Chem. 1962 66 249. 1529. N C. Li J. M. White and R. L. Yoest J. Ainer. Chem. SOC. 1956 78 5218. CROW AND WESTWOOD COMPLEXED METAL IONS 75 ratios with mean values of AHo of -3.94 -8.10 and -12.14 kcal. respectively for the overall reactions over the temperature range 0-45’. A regular increase of AHo thus occurs with each ligand attachment with a corresponding negative entropy increase. The variability in entropy values for complex-formation is well shown by the values obtained for the mercury(Ir) cadmium and zinc complexes with ethylenediamine with values of -5 +3.4 and +10.7 e.u.re~pectively,~~ and more recently by the cadmium complexes of histamine and related compounds 73 where ASo varied from -19 e.u. for antistine to +4 e.u. for benadryl. The loss of translational degrees of freedom by ligand attachment would suggest a greater degree of order and hence a negative entropy value but this may be offset by a loss of hydration of the metal ion. The latter may in fact be sufficient to swing the value over to the positive side. The field force due to the central ion may still be sufficient to maintain some degree of order- ing of the solvent outside the sphere of the ligand (the “iceberg” concept of Frank and Wen74).With a multidentate ligand more water tends to be displaced from the metal ion and the entropy changes are greater. The entropy values give some indications as to the nature of the complex and show whether inner-sphere or outer-sphere complexes are formed. FIG. 6. Plots of loglo kj against (j - 1) for several systems of complexes. 0 Cu-F I3 (ref. 5). Cd-OX*- (ref. 16). a Cd-N8+ (ref. 15). 0 Cd-thiourea (T. J. Lane “Advances in Polarography,” Pergamon London. 1960 vol. 2 p. 797). 0 Pb- thiourea (ref. as for Cd-thiourea). 72 D. K. Roe D. B. Masson and C. J. Nyman Analyt. Chem. 1961,33 1464. 73 A. C. Andrews and J. Kirk Romary J. 1964,405. 74 H. S . Frank and W. Y . Wen Discuss. Fmaaby Soc. 1957 24 133. 76 QUARTERLY REVIEWS The values of the stability constants for step-wise complexes show an interesting correlation.Van Panthaleon van E c ~ ' ~ suggested a relationship of the form where X is an empirical parameter for each system. This however appears to have been little exploited. Accordingly values for some of the systems which have been reported have been calculated from the overall step constants and are shown in the form of a graph of log, Kj against ( j - 1) (see Fig. 6). These systems give reasonably linear graphs and this suggests an equal change in free energy at each increase in ligand. How- ever in some systems e.g. cadmium thiocyanate,12 the results are not so encouraging. 8. Conclusion Few methods are available for studying step-wise complex-formation in solution and of these the polarographic method has some advantage over spectral methods since the identification and the determination of the properties of more species is possible simultaneously.However it must be admitted that since the measurement of very small differences in half-wave potentials is often involved the accuracy in the determination of the higher stability constants so far obtained is often not as great as is desired. This is unfortunate since the potentialities for obtaining thermo- dynamic data are considerable. There are however indications that recent workers are realising these advantages and greater care is being observed over solution factors. More information is required for families of compounds of similar composition to relate general electrode behaviour with structure. So far only cobalt compounds have been studied in considerable detail particularly by Vlcek but other elements e.g. chromium rhodium and iridium would be interesting. In particular there is wide scope for studying the electrode mechanisms of complex species. This is not an easy field being somewhat bedevilled by the complications arising from the electrical double layer but is a fascinating and rewarding one. 75 C. L. van Panthaleon van Eck Rec. Trav. chim. 1953 72 529.

ISSN:0009-2681    

DOI:10.1039/QR9651900057

出版商:RSC    

年代:1965

数据来源: RSC

摘要:

CUMIUTATI'VE INDEXES VOLUMES I-XIX (1 947-1 965) CUMULA Abel E. W. 17,133 Abrahams S. C. 10,407 Abrikosova I. I. 10 295 Addison C. C. 9 115 Ahrland S. 12 265 Albert A. 6 197 Allen G.. 7 255 Amphlett. C. B. 8 219 Anderson J. E. 19 426 Anderson J. S. 1 331 Angyal S . J. 11 212 Ansell M. F. 18 211 Arotsky J. 16 282 Amstein H. R. V. 4,172 Atherton F. R. 3 146 Avison A. W. D. 5 171 Bacon R. G. R. 9 287 Baddeley G. 8 355 Baddiley J. 12 152 Badger G. M. 5 147 Bagnall K. W. 11 30 Baker W. 11 15 Baltazzi E. 9 150 Barker S. A. 7 58 Barltrop J. A. 12 34; Barnartt S. 7. 84 Barrer R. M. 3 293 Barton D. H. R. 3 36; 10,44; 11 189 Bassett H. 1 247 Bateman L. 8 147 Battersby A. R. 14 77; Baughan E. C. 7 103 Baulch D. L. 12 133 Bawn C. E. H. 16. 361 Bayliss N. S. 6 319 Beattie I. R. 17 352 Bell R.P. 1 113; 2 132; 13 169 Bentley R. 4 172 Bergel F. 2 349 Berry M. 17 343 Bethell D. 12 173 Bevington J. C. 6 141 Birch A. J. 4 69; 12 17 Bircumshaw L. L. 6 Bockris J. O’M. 3 173 Bolland J. L. 3 1 Bond G. C. 8 279 Bourne E. J. 7 58 19,95 16 117 15 259 I57 TIVE INDEX OF Bowen E. J. 1 1 ; 4,236 Bradley R. S.. 5 315 Braude E. A. 4 404 Brernner J. G. M. 2 1 Brink N. G. 12 93 Brown B. R. 5. 131 Brown D. 17 289 Brown R. D. 6 63 Buchanan 3. G. 12,152 Buckingham A. D. 13 Bu’Lock J. D. 10 371 Bunnett J. F. 12 1 Burkin A. R. 5 1 Burnett G. M. 4 292 Burton H. 6 302 Cadogan J. I. G. 8,308; Caldin E. F. 7 255 Capon. B. 18,45 183 16,208 Carrington A. 14,427; 17.67 Challenger F. 9 255 Chatt J. 12 265 Child W. C. jun. 18 32 1 Clark J. 18 295 Clayton R. B. 19 168 Coates G. E. 4 217 Collins C. J. 14 357 Collinson E.9 31 1 Colton R. 16 299 Cook A. H. 2 203 Cook J. W. 5 99 Cookson R. C. 10 44 Cooper C. F. 13 71 Cottrell T. L. 2. 260 Coulson C. A. 1 144 Cowdrey W. A. 6 358 Cox E. G. 7 335 Crawford V. A. 3,226; Croft R. C. 14 1 Crofts P. C. 12 341 Crombie L. 6 101 Cross A. D. 14. 317 Crow 19. R. 19 57. Cruickshank D. W. J. Curran S. C. 7 1 Cuthbert J. 13 215 Dainton F. S. 12 61 Dalgliesh C. E. 5 227 442 20 I 14 378 7 335 AUTHORS Davies A. G. 9 203 Davies D. S. 6 358 Davies M. 8 250 Davies N. R. 12 265 Davies R. 0.. 11. 134 Dawton R. H. V. M. De Heer J. 4 94 de la Mare P. B. D. 3 Delpierre G. R. 19 de Mayo P. 11 lS9; Derjaguin B. V. 10,295 Dickens P. G. 11 291 Downing D. F. 16 133 Doyle W. T. 14 62 Dubinin M. M. 9 101 Duncan J. F. 2 307; 12 133 19 36 Dunning W. J. 9 23 Eastham J.F. 14 221 Edwards P. A. 19 369 Eley D. D. 3 181 Emelkus H. J. 2 132 Errede L. A. 12 301 Evans M. G. 4 94; 6 Evans R. M. 13 61 Fensham P. J. 11 227 Ferrier R. J. 13 265 Field B. O. 18 361 Fish A. 18 243 Flowers M. C. 18 122 Fluendy M. A. D. 16 Foster A. B. 11 61 Fowles G. W. A. 16 19 Freidlina R. Kh. 10 Gascoigne R. M. 9,328 Gaydon A. G. 4 l Gee G. 1 265 Gent W. L. G. 2 383 Gibson D. T. 3 263 Gillespie R. J. 2 277; Gilman H. 13 116 Glasser F. P. 16 343 Glasser L. S. Dent 16 Glenn A. L. 8 192 991 126 329 15 393 156 24 1 330 8 40; 11 339 343 CUMULATIVE INDEX 443 Goehring M. 10 437 Gold. V. 9 51; 12 173 Golding R. M. 19 36 Gowenlock B. G. 12 Gray P. 9 362; 17,441 GrdeniC D. 19 303 Green J. H. S. 15 125 Greenwood N. N. 8 1 Griffith J. S.. 11. 381 Griffith W. P. 16 188 Grove J. F.15,56; 17,l Gruen D. M. 19 349 Gundry P. M. 14 257 Gunstone F. D. 7 175 Gutmann v. 10 451 Halpern J. 10 463; 15 Halsall T. G. 16 101 Hamer F. M. 4 327 Hardy C. J. 18 361 Hardy D. V. N. 2 25 Harman R. E. 12 93 Harris M. M. 1 299 Hartley G. S. 2 154 Hartley S. B. 17 204 Hassel O. 7 221; 16 1 Hawkins E. G. E. 4 Hawkins J. D. 5 171 Haynes L. J. 2 46; 14 Heaney H. 11 109 Hey D. H. 8 308 Hickling A. 3 95 Hill H. A. O. 19 95 Hochstrasser R. M. 14 Hodson H. F. 14,77 Hoffman C. J. 18 113 Holmes W. S. 17 204 Holt R. J. W. 13 327 Hughes E. D. 2 107; 5 245; 6 34 Hulett J. R. 18 227 Hush N. S. 6 186 Ingold C. K. 6 34; Irving H. M. 5 200 Ivin K. J. 12,61 Jacobs P. W. M. 6,238 Jacques J. K. 17,203 Jain A. C. 10 169 321; 14 133 19,254 207 25 1 292 1 46 11 1 Janz G. J. 9 229; 17 JeRrey G. A. 7 335 Jenkins E.N. 10 83 Jennings K. R. 12 116; Jones D. G. 4 195 Kapustinskii A. F. 10 Katritzky A. R. 10 Kenyon J. 9 203 Khorana H. G.. 6 340 Kipling J. J. 5,60; 10 1 Kiselev A. V. 15 99 Kitchener J. A. 13 71 Lagowski J. J. 13 233 Lamb. J. 11 134 Lamberton A. H. 5 75 Lamchen M. 19 329 Law H. D. 10 230 Lea F. M. 3 82 Ledwith A. 16 361 Leech H. R. 3 22 Leisten J. A. 8 40 Levy N. 1 358 Lewis E. S. 12 230 Lewis J. 9 115 Lifshitz E. M. 10 295 Linnett J. W. 1 73; 11 291 ; 12,116 Lister B. A. J. 2,307 Lister M. W. 4 20 Livingston R. 14 174 Livingstone S. E. 19 Long L. H. 7 134 Longuet-Higgins H. C. 11 121; 14 427 Loudon J. D, 5,99; 18 389 Luttke W. 12 321 Lythgoe B. 3 181 Maccoll A. 1 16 McCoubrey J. C. 5 364; 11 87; 17 204 MacDiarmid A. G. 10 208 McGrath W. D. 11 87 McKenna J. 7 231 McLaughlin E.14,236 Maddock A. G. 5,270; Maitland P. 4 45 225 15 237 283 395; 13 353 386 17,289 Manners D. J. 9 73 Marsh J. K. 1 126 Martin F. S. 13 327 Martin R. L. 8 1 Mason S. F. 15 287; Megson N. J. L. 2 25 Mellor J. M. 18,270 Millar I. T. 11 109 Millen D. J. 2 277 Mole M. F. 17 204 Morgan K. J. 8 123; Morrison A. L. 2 349 Munavalli S. 18 270 Murrell J. N. 15 191 Musgrave W. K. R. 8 Nancollas G. H. 14 Nelson Smith R. 13 Nesmeyanov A. N. 10 Newth F. H. 13 30 Nicholls D. 36 19 Norrish R. G. W. 10 Nyholm R. S. 3 321; 7 377; 11,339 Ollis W. D. 11 15 Orgel L. E. 8 422; 11 Orville-Thomas W. J. Overend W. G. 11 61; Owston P. G. 5 344 Paddock N. L. 18 168 Page J. E. 6 262 Palmer M. H. 18 211 Paneth F. A. 2,93 Parker A. J. 16 163 Parsonage N G. 13 Pauson P. L. 9 391 Payne D. S. 15 173 Peacock R.D. 16 299 Pepper D. C. 8 88 Percival E. G. V. 3 369 Perrin D. D. 18 295 Phillips F. C. 1 91 Pilcher G. 17 264 Plimmer J. R. 14 292 17. 20 12,34 33 1 402; 18 1 287 330 149 38 1 11 162 13,265 306 444 QUARTERLY REVIEWS Pople J. A. 11 273 Porter G. B. 14 146 Praill P. F. G. 6 302 Pritchard H. O. 14 46 Purdie N. 18 1 Rabinovitch B. S. 18 Reid C. 12 205 Reid D. H. 19 274 Reid S. T. 15 393 Richards R. E. 10,480 Ridd J. H. 15 418 Riddiford A. C. 6 157 Riley H. L. 1,59; 3 160 Roberts H. L. 15 30 Roberts L. E. J. 15,442 Roberts M. W. 16.71 Rsmming Chr. 16 1 Rogers N. A. J. 16 117 Rose J. D. 1 358 Rowlinson J. S. 8 168 Satchel] D. P. N. 9,51; Saxton J. E. 10 108 Schofield K. 4 382 Scott A. I. 19 1 Sehnan. S. 14 221 Seshadri T. R. 10 169 Sexton W. A. 4,272 Sharpe A. G. 4 115; Shchukina L.A, 10 Sheldon J. C. 14,20@ Shemyakin M. M. 10 Sheppard N. 6 l 7 19 Shooter K. V. 19 369 Siegel B. 19 77 Sillen L. G. 13 146 Simes J. J. H. 9 328 Simons P. 13. 3 Simpson D. M. 6 1; 7 122 17 160 11,49 26 1 261 19 Skinner H. A. 17 264 Smales A. A. 10 83 Smith B. C. 14 200 Smith E. B. 16 241 Smith H. 12 17 Smith J. A. S. 7 279 Smith M. L. 9 1 Springall H. D. 10 230 Stacey M. 1 179 213 Staveley L. A. K. 3,65; Steele D. 18 21 Stephens R. 16 44 Stem E. S. 5 405 Stone F. G. A. 9 174 Stothers J. B. 19 144 Sutton L. E. 2 260 Swallow A. J. 9 3 11 Symons M. C. R. 12 230; 13 99; 14 62; 16 282 Synge R. L. M. 3 245 Szwarc M. 5 22; 12 13,306 301 Tatlow J. C. 16 44 Taylor A. W. C. 4 195 Taylor M. F. W. 16 Tedder J. M. 14 336 Tennant G. 18 389 Theobald D. W. 16 Thomas J. M. 19 231 Thomas S. L.7 407 Thomson R. H. 10,27 Thrush B. A. 10 149 Tipper C. F. H. 11,313 Tompkins F. C. 6 238; Topley B. 3 315 Trapnell B. M. W. 8 Trippett S. 17. 406 343 101 14,257 404 Trotman-Dickenson A. Truter E. V. 6,390 Turner A. B. 18 347 Turner E. E. 1 299 Turner H. S. 7 407 Ubbelohde A. R. 4 356; 5,364; 11,246 Ulbricht T. L. V. 13,48 Uri N. 6 186 Vainshtein B. K. 14 Wait S. C. 17 225 Walsh A. D. 2 73 Walton G. N. 15 71 Walton R. A. 19 126 Warburton W. K. 8,67 Warhurst E. 5 44 Waters W. A. 12 277 Weale K. E. 16 267 Weedon B. C. L. 6 380 Wells A. F. 2 185; 8 Wells R. A. 7 307 Westwood J. V. 19 57 Whiffen D. H. 4 131; White E. A. D. 15 1 Whytlaw-Gray R. 4 Wilkins R. G. 16,316 Wilkinson S. 15 153 Williams A. 17 243 Williams B. R. 19 231 Williams F. 17 101 Wilson H. N. 2 1 Wittenberg D. 13 116 Wood J.L. 17 362 Woodward L. A. 10 Woolf A. A. 15 372 Yoffe A. D. 9 362 Zakharkin L. I. 10,330 F. 7 198 105 3 80 12,250 153 185 CUMULATIVE INDEX OF TITLES Absorption spectra molecular elec- tronic 15 287 Acceptor properties of quadripositive silicon germanium tin and lead 17 382. Acetylenes as natural products 10 371 Acetylenes infrared and Raman spectra of 6 1 Acid use of the term 1 113 Acids carboxylic anodic syntheses with 6 380 Acids carboxylic association of 7 255 Acids straight-chain fatty natural and synthetic recent developments in the preparation of 7 175 Acids tetronic 14 292 Acid-base reactions simple rates of Actinide oxides 15.442 Acylation an outline of 17 160 Addition polymerisation at high pres- sures 16 267 Addition polymerisation stereo- regular 16 361 Addition reactions free-radical of olefinic systems 8 308 Adsorption energy adsorption equili- bria and surface chemistry 15 99 Adsorption of non-electrolytes from solution 5,60 Affinities relative of ligand atoms for acceptor molecules and ions 12,265 Age geological determination of by radioactivity 7 1 Aldehydes polymerisation of 6,141 Aliphatic compounds saturated inter- action of free radicals with 14 336 Alkaloid biosynthesis 15 259 Alkaloids of calabash-curare and Strychnos species 14 77 Alkaloids ergot 8 192 Alkaloids indole excluding harmine and strychnine 10 108 Alkaloids steroidal 7 23 1 Alkaloids veratrum 12 34 Alkanes infrared and Raman spectra Alkanes tetra- and tri-chloro- and Analgesics synthetic 2 349 Analysis conformational principles 13 169 of 7 19 related compounds 10 330 of 10 44 Analysis inorganic applications of solvent extraction to 5 200 Analysis radioactivation 10 83 Anionotropy 4.404 Anions in dipolar aprotic solvents effects of solvation on the proper- ties of 16 163 Anodic syntheses with carboxylic acids 6,380 Antibiotics newer chemistry of 12,93 Antibiotics macrolide 17 343 Aromatic reactions promoted by cop- per 19 95 Arrhenius equation deviations from 18,227 Arrhenius factors (frequency factors) in unimolecular reactions 14,133 Aspects physicochemical of some recent work on photosynthesis 14 174 Association of carboxylic acids 7,255 Asymmetry the non-conservation of parity and optical activity 13 48 Atoms in the gaseous phase produc- tion detection and estimation of 15 237 Attraction molecular direct measure- ment of between solids separated by a narrow gap 10,295 Azicles inorganic chemistry of the 17 441.Base use of the term 1 1 13 Benzilic acid and related rearrange- ments 14 221 Biological reactions r81e of phosphoric esters in 5 171 Biosynthesis alkaloid 15 259 Biosynthesis of sterols steroids and terpenoids. Part 1. Biogenesis of cholesterol and the fundamental steps in terpenoid biosynthesis. Part 2. Phytosterols terpenes and the physiologically active steroids 19 168 201 Bond aromatic 5 147 Bond chemical in crystals applica- tion of electron diffraction to the study of 14 105 Bond-cnergy term values in hydro- carbons and related compounds 17 264 Bonding chemical and nuclear quad- rupole coupling 11,162 445 446 QUARTERLY REVIEWS Bonds dissociation energies of 5 22 Bonds interpretation of properties of 2 260 Bonds weak charge-transfer in solids containing chemically saturated molecules direct structural evi- dence for 16 l Borazoles the 14 200 Boron hydrides chemistry of 9 174 Boron hydrides and related com- Boron trifluoride co-ordination com- pounds 2.132 pounds of 8 1 Carbides of iron 3 160 Carbohydrate epoxides 13 30 Carbohydrate phosphates 11 61 Carbohydrate sulphates 3. 369 Carbohydrates newer aspects of stereochemistry of 13 265 Carbon amorphous and graphite 1 59 Carbon-l 3 nuclear magnetic resonance spectroscopy 19 144 Carbon-carbon bonds oxidative hydrolysis of in organic molecules 10 261 Carbon-carbon double bonds geo- metrical isomerism about 6 101 Carbon-hydrogen bond polarity of 2 383 Carbon-hydrogen bonds mechanism of breakage of 12 230 Carbon-oxygen surface compounds of 13,287 Carbon-phosphorus bonds com- pounds containing 12 341 Carbonitrides of iron 3 160 Carbonium ions structure of 12 I73 Carbons active study of porous structure of by a variety of methods 9 101 Carbons adsorbent properties and nature of 10 1 Carbonyls.metal 17 133 Carbonyls of metals chemistry of 1 33 1 Catalysis by metals specificity in 8 404 Catalysis of reactions involving hydro- gen mechanisms of 3,209 Catalysis and semiconductivity 11,227 Catalysts redox initiation of poly- merisations by 9 287 Cations halogen 16 282 Cations organic reactions of 6 302 Charcoals active study of porous structure of by a variety of methods 9 101 Charge-transfer bonds weak in solids containing chemically saturated molecules direct structural evidence for 16 1 Charge-transfer spectra theory of 15 191 Chemical activation 18 122 Chemical bonding Mossbauer studies of 19 36 Chemisorption of gases on metals 14 257 Chromatography inorganic 7 307 Chromium mechanisms of oxidation by compounds of 12 277 Clathrates molecular interactions in a comparison with other condensed phases 18 321 Collisions in gases energy transfer in 11 87 Colloidal electrolytes state of solution of.2 154 Colour and constitution 1 16 Colour centres in alkali halide crystals 14 62 Combustions slow in the gas phase elementary reactions in 11 313 Complex compounds stabilities of 5 I Complexed metal ions polarographic study of 19 57 Complexes cyanide of the transition metals 16 188 Compounds containing sulphur- fluorine bonds chemistry of 15 30 Conductance ionic in solid salts 6 238 Configuration of flexible organic molecules 5 364 Conformational analysis principles of 10 44 Conjugated compounds free-electron approximation for 6 319 Co-ordination compounds of boron trifluoride 8 1 Co-ordination compounds kinetics and mechanism of replacement reactions of.16 31 6 Copper-promoted reactions in aro- matic chemistry 19 95 Coupling oxidative of phenolic com- pounds 19 1 CUMULATIVE INDEX 447 Crystal growth kinetics of 18 1 Crystal structure and melting 4 356 Crystal structures of salt hydrates and complex halides 8 380 Crystal line transit ion- metal com- pounds electron resistance in 14,427 Crystals alkali halide colour centres in 14 62 Crystals chemical bonds in applica- tion of electron diffraction to the study of 14 105 Crystals location of hydrogen atoms in 10 480 Crystals ionic lattice energy of 10 283 Cyanide complexes of the transition metals 16 188 Cyanides alkyl reactions with metal halides 19 126 Cyanine dyes 4 327 Cyclohexane stereochemistry of 7 22 1 Cyclisation of olefinic acids to ketones and lactones 18,211 Deamination nitrosation and di- Decarboxylation thermal mechanism azotisation 15,41 S of 5 131 Degradation biological of trypto- Dhan.5. 227 Densities,’limiting 4 153 Deoxyribonucleic acid macro- molecular structure and properties of 19 369. Di- and tri-terpenes synthesis of 16 117 Diazotisation nitrosation and de- amination 15 418 Dielectric absorption. 8 250 Dihalogen compounds Grignard and organolithium compounds derived from 11 109 Disproportionation in inorganic corn- pounds 2 1 Diterpenoids chemistpj of 3 36 Dyes effect of light on 4 236 Dyes cyanine 4 327 Dyes organic and their constitution 1 16 Earth distribution of the elements in Electrode processes in aqueous solu- the 3 263 tions mechanism of 3 95 Electrolytes effects of ultrasonic waves on 7 84 Electrolytes colloidal state of solu- tion of 2 154 Electromagnetic separation of stable isotopes 9 1 Electron correlation and chemical consequences 11 29 1 Electron resistance in crystalline trans- ition-metal compounds 14 427 Electron-spin resonance spectra of aromatic radicals and radical-ions 17 67 Electron transfer and related processes in solution mechanism of 15 207 Electronic absorption spectra mole- cular 15 287 Electrons structures of molecules deficient in 11 121 Elements terrestrial distribution of 3 263 Elements heavy radioactivity of 5 270 Elements of Group VITI recent stereochemistry of 3 321 Elements of Groups IVB and IV comments on the thermochemistry of 7 103 Elements of the rare-earth series separation of 1 126 Elements transuranic chemistry of 4 20 Elements vapours of the 19 77 Energy adsorption and adsorption equilibria in surface chemistry 15 99 Energy transfer of in gaseous collisions 11 87 Enzymes degradation of polysacchar- ides by 9 73 Enzymes synthesis of polysaccharides by 7 58 Epoxides of sugars 13 30 1,2-Epoxides naturally-occurring the chemistry of 14 317 Equilibria adsorption and adsorption energy in surface chemistry 15 99 Equilibria hydrolytic quantitative studies of 13 146 Equivalent-orbital approach to mole- cular structure 11 273 Ergot alkaloids structure of 8 192 Esters carboxylic and related com- pounds alkyl-oxygen heterolysis in 9,203 448 QUARTERLY REVDEWS Exchange reactions of hydrogen iso- topes in solution principles of 9 51 Extraction liquid-liquid in inorganic chemistry 13 327 Far-infrared spectroscopy 17 362 Ferrocene and related compounds 9 Fission nuclear 15 71 Flames emission spectra of 4 1 Flames methods of studying chemical kinetics in 17 243 Flash photolysis and kinetic spectro- scopy 10 149 Flavones nuclear methylation of 10 169 Fluorine-sulphur bonds compounds containing 15 30 Fluorescence and fluorescence quench- Fluorine laboratory and technical production of 3 22.Fluorine compounds general aspects of the inorgdnic chemistry of 11,49 Fluorine compounds laboratory and technical production of 3 22 Fluorine compounds organic reac- tions of 8 331 Fluorocarbon chemistry.Part 1. Fluorination of organic com- pounds 16,44 Foaming current concepts in theory of 13 71 Force constants 1 73 Forces intermolecular and the pro- perties of matter 8 168 Free-electron approximation for con- jugated compounds 6 319 Friedel-Crafts reaction modern aspects of 8 355 Furans some aspects of the chemistry of 4 195 Fused-salt spectrophotometry 19 349 Gases adsorbed infrared spectra of 14,378 Gases chemisorption of on metals 14,257 Gases elementary reactions in slow combustions in 11 313 Gases energy transfer in collisions in 11,87 Gas-phase oxidation and related pro- cesses radical rearrangement in 18 243 Gemstones synthetic 15,l 39 1 ing,. 1 1 Germanium acceptor properties of Gibberellins 15 56 Graphite and amorphous carbon 1 Graphite lamellar compounds of Grignard reagents derived from di- Griseofulvin 17 1 quadrispositive 17 382 59 14 1 halogen compounds l l 109 Halide alkali crystals colour centres in 14 62 Halides of the phosphorus group elements (P As Sb Bi) 15 173 Halides complex crystal structures of 8 380 Halides reactions of in solution 5 245 Halogens kinetics of thermal addition of to olefins 3 126 Heats of formation of simple in- organic compounds 7 134 Heteroaromatic compounds infrared spectra of 13 353 Heterogeneous reactions transport control in 6 157 Heterolysis alkyl-oxygen in carb- oxylic esters and related compounds 9,203 Hydrocarbons and related compounds bond-energy term values in 17 264 Hydrocarbons infrared and Raman spectra of.Part I acetylenes and olefins 6 1. Part 11 paraffins 7 19 Hydrocarbons radiation chemistry of 17 101 Hydrogen molecular homogeneous reactions of in solution 10 463 Hydrogen atoms location of in crystals 10 480 Hydrogen catalysis mechanisms of 3 209 Hydrogen isotope exchange reactions in solution principles of 9,51 Hydrogen peroxide its radicals and its ions energetics of reactions involving 6 186 Hydrogenation catalytic and related reactions mechanism of 8 279 Hyperconjugation 3,226.Ice structure of 5,344 Immunochemistry aspects of 1 179 a* * L13 CUMULATI'vE INDEX 449 Indole alkaloids excluding harmine Induction asymmetric and asym- Infrared absorption bands absolute Infrared spectra of adsorbed gases 14 Inorganic azides chemistry of the 17 Inorganic chemistry and magnetism Inorganic compounds disproportiona- Inorganic compounds Raman spectra Inorganic compounds stereochemistry of 11,339 Inorganic compounds simple heats of formation of 7 134 Inorganic nitrates and nitrato-com- pounds 18 361 Inorganic oxy-compounds topotactic reactions in 16 343 Inorganic reactions in liquid am- monia 16 19 Inositols 11 212 Insecticides synthetic structure and activity in 4 272 Intensities absolute of infrared ab- sorption bands 18 21 Interaction of free radicals with saturated aliphatic compounds 14 336 Interactions molecular in clathrates a comparison with other condensed phams 18 321 Interactions substituent in ortho- substituted nitrobenzenes 18,389 Interhalogen compounds and poly- halides 4 1 15 Intermolecular forces and some pro- perties of matter 8 168 Iodine compounds inorganic some reactions of 8 123 Ion association in aqueous solution thermodynamics of 14 402 Ion exchange 2 307 Ionic melts vibrational spectra of 17 225 Ionisation potentials and far ultra- violet spectra their significance in chemistry 2 73 Ions complexed metal studied polaro- graphically 19 57 and strychnine 10 108 metric transformation 1 229 intensities of 18 21 378 44 1 7,377 tion in 2 l of 10 lS5 Iron carbides nitrides and carbo- nitrides of 3 160 Isoflavones 8 67 Isomerism.geometrical about carbon- carbon double bonds 6 101 Isotopes exchange of between different oxidation states in aqueous solution. 8 219 Isotopes synthesis of organic com- pounds labelled with 7 407 Isotopes tracer techniques involving 4 172 Isotopes stable electromagnttic separation of 9 1 Kinetics and mechanism of replace- ment reactions of co-ordination compounds 16 316 Kinetics in flames methods of study- ing chemical 17 243 Kinetics of crystal growth 18 I Lactones physiologically active un- saturated 2 46 Lamellar compounds of graphite 14 1 Lanthanons separation of 1 126 Lattice energy of ionic crystals 10 283 Lead acceptor properties of quadri- positive 17 382 Ligand atoms relative affinities of for acceptor molecules and ions 12 265 Ligands metal complexes of contain- ing sulphur selenium or tellurium as donor atoms 19 386 Ligand-field theory 11 381 Light absorption of and photo- chemistry 4 236 Liquids transitions in 3 65 Liquids transport properties of in relation to their structure 14 236 Liquids ultrasonic analysis of relaxa- tion processes in 11 134 Macrolide antibiotics 17 343 Macromolecular structure and pro- perties of deoxyribonucleic acid 19 369 Magnetic resonance absorption nuclear 7 279 Magnetism and inorganic chemistry 7 377 Manganese mechanisms of oxidation by compounds of 12,277 450 QUARTERLY REVIEWS Manganese dioxide oxidations by in neutral media 13 61 Mass spectrometry application of to chemical problems 9 23 Mass spectrometry of free radicals 13 215 Mechanisms of electron transfer and related processes in solution 15 207 Melting and crystal structure 4.356 Mercury structural chemistry of 19 Meso-ionic Compounds 11 15 Metal carbonyls 17 133 Metal complexes of ligands con- taining sulphur selenium or tellur- ium as donor atoms 19,386 Metal halides reactions with alkyl cyanides 19 126 Metal oxidation 16 71 Metal-amine solutions reduction by; applications in synthesis and deter- mination of structure 12 17 Metal-ammonia solutions reduction of organic compounds by 4 69 Metal-transition compounds crystal- line electron resistance in 14 427 Metals chemisorption of gases on 14 257 Metals nature of solutions of 13 99 Metals specificity in catalysis by 8 Methyl radicals reactions of 7 198 Methylation biological 9 255 Methylation nuclear of flavones and related compounds 10 169 Mossbauer studies of chemical bond- ing 19 36 Molecular electronic absorption spectra 15 287 Molecular interactions in clathrates a comparison with other condensed phases 18 321 Molecular-orbital approach to mole- cular structure 11 273 Molecular-sieve action of solids 3 293 Molecules determination of structure of by X-ray crystal analysis modern methods and their accuracy 7,335 Molecules molecular-orbital and equivalent-orbital approach to structure of 11 273 303 404 Molecules electron deficient struc- tures of 11 121 Molecules electronically excited reac- tions of in solution 13 3 Molecules flexible organic configura- tion of 5 364 Molecules organic oxidative- hydro- lysis of carbon-carbon bonds in 10 26 1 Molecules simple representation of by molecular orbitals 1.144 Monte Carlo methods application of to physicochemical problems 16 24 1 Morphine synthetic approaches to structure of 5,405 Muscarine history and chemistry of 15 153 Neighbouring group participation 18 45 Nitramines some aspects of the chemistry of 5 75 Nitrates inorganic and nitrato-com- pounds 18,361 Nitration of aromatic compounds 2 277 Nitration of heterocyclic nitrogen compounds 4,382 Nitrides of iron 3 160 Nitrobenzenes ortho-substituted sub- stituent interactions in 18,389 Nitro-compounds aliphatic 1 358 Nitrogen active 12 116 Nitrogen compounds heterocyclic nitration of 4 382 Nitrogen dioxide-dinitrogen tetroxide system structure and reactivity of 9 362 Nitrones 19 329 Nitrosation diazotisation and de- amination 15 418 C-Nitroso-compounds structure and properties of 12 321 Nitrosyl group chemistry of 9 115 Non-electrolytes adsorption of from Non-electrolytes theories of solutions Nuclear chemistry quantitative 12 Nuclear fission 15 71 Nuclear magnetic resonance absorp- solution 5 6 0 of 13 306 133 tion 7,279 CUMULATIVE INDEX 45 1 Nuclear quadrupole coupling and chemical bonding 11 162 Nucleation.in phase changes 5 3 15 Nucleotide coenzymes recent develop- ments in biochemistry of 12 152 Oceans salt deposits from 1 91 Olefinic acids cyclisation of to ketones and lactones 18 211 Olefinic systems free-radical addition reactions of 8,308 Olefins infrared and Raman spectra of 6 1 Olefins kinetics of oxidation of 3 l Olefins kinetics of thermal addition of halogens to 3 126 Olefins oxidation of 8 147 Optical activity and non-conservation of parity 13,48 Optical rotatory power 17 20 Orbitals molecular approach to mole- cular structure through 11 273 Orbitals molecular and organic reactions 6 63 Orbitals molecular representation of simple molecules by 1 144 Organic bases prediction of the strengths of 18 295 Organic compounds action of ionising radiations on 9 3 11 Organic compounds behaviour of in sulphuric acid 8 40 Organic compounds estimation of thermodynamic properties for 9 229 Organic compounds fluorination of 16 44 Organic compounds isotopically labelled synthesis of 7 407 Organic Compounds polarography of 6 262 Organic compounds reduction of by metal-ammonia solutions 4.69 Organic compounds tervalent of phosphorus oxidation of 16 208 Organic oxygen compounds thermo- dynamic properties of 15,125 Organic reactions and molecular orbitals 6 34 Organolithium reagents derived from dihalogen compounds 11 109 Organometallic compounds of the first three periodic groups 4 217 Organosilylmetallic compounds for- mation and reactions of 13 116 Osmium and its compounds 19 254 5-Oxazolones chemistry of 9.150 Oxidation by compounds of chro- mium and manganese mechanisms of 12 277 Oxidation metal 16 71 Oxidation of olefins 3 1; 8 147 Oxidation of tervalent organic com- pounds of phosphorus 16 208 Oxidation-reduction potential of quinones relation of to chemical structure 4 94 Oxides actinide 15 442 Oxides of metals structures of 2 185 N-Oxides aromatic heterocyclic chemistry of 10 395 Oxy-compounds inorganic topotactic reactions in 16 343 Oxygen compounds organic thermo- dynamic properties of 15 125 Oxygen and carbon surface com- pounds of 13,287 Parity non-conservation of 13 48 Penicillins chemistry of 2 203 Peptides methods of synthesis and terminal-residue studies of 10 230 Peptides naturally occurring 3 245 Peptides structural investigation of Pe~fluoroalkyl derivatives of metals Peroxides organic and their reactions Phase changes nucleation in 5 315 Phenalenes the chemistry of 19 274 Phenolic compounds oxidative coupl- Phenols tautomerism of 10 27 Phosphates of carbohydrates 11 61 Phosphates condensed 3 345 Phosphoni trilic derivatives and related compounds 18 168 Phosphoric esters r6le of in biological reactions 5 171 Phosphorus compounds thermo- chemical properties of 17 204 Phosphorus group elements (P As Sb Bi) halides of 15 173 Phosphorus oxidation of tervalent organic compounds of 16,208 Phosphorus oxyacids some aspects of the organic chemistry of derivatives of 3 146 6,340 and non-metals 13,233 4,251 ing of 19 1 452 QUARTERLY REVIEWS Photochemical rearrangements and Photochemistry and light absorption Photography cyanine dyes in 4 327 Photo-oxidation primary processes in 14 146 Photopolymerisation 4 236 Photosynthesis physicochemical aspects of some recent work on 14 174 Phthalocyanines semiconductivity of 18 113 Physicochemical problems application of Monte Carlo methods to 16,241 Pinacol rearrangement 14 357 Polarity of the carbon-hydrogen bond 2 383 Polarography of organic compounds 6,262 Polonium chemistry of 11 30 Polyhalides and interhalogen com- pounds 4 115 Polymerisation of aldehydes 6 141 Polymerisation addition at high pressures 16 267 Polymerisation addition some thermodynamic and kinetic aspects of 12 61 Polymerisation addition stereo- regular 16 361 Polymerisation induced by light 4 236 Polymerisation initiation of by redox catalysts 9 287 Polymerisation ionic 8 88 Polymerisation radical rate constants in 4 292 Polymers based on silicon chemistry of 2 25 Polymers high thermodynamic pro- perties of and their molecular interpretation 1 265 Polysaccharides enzymic degradation of 9 73 Polysaccharides enzymic synthesis of 7 58 Portland cement constitution of 3 82 Processes primary in photo-oxidation 14 146 Production detection and estimation of atoms in the gaseous phase 15 237 Protactinium 17 259 related transformations 15 393 4.236 Proteins structural investigation of 6 Psychotomimetic substances 16 133 Pteridines 6 197 Purines some aspects of the chemistry of 3 181 Pyrans some aspects of the chemistry of 4 195 Pyrimidines some aspects of the chemistry of 3 181 Pyrrole pigments biogenetic origin of 4 45 Quadrupole coupling nuclear and chemical bonding 11 162 Quadrupole moments molecular 13 183 Quenching of fluorescence 1 1 Quinone methides 18 347 Quinones relation between the oxida- tion-reduction potential and chem- ical structures of 4 94 Radiation chemistry of hydrocarbons 17 101 Radiations ionising action of on organic compounds 9,3 1 1 Radical rearrangement in gas-phase oxidation and related processes 18 243 Radicals aromatic and radical-ions electron-spin resonance spectra of 17 67 Radicals free electron resonance spectroscopy of 12 250 Radicals free interaction of with saturated aliphatic compounds 14 336 Radicals free mass spectrometry of 13 215 Radioactivation analysis 10 83 Radioactivity determination of geo- logical age by 7 1 Radioactivity of the heavy elements 5 270 Keaction Wittig.17,406 Reactions copper-promoted in aro- matic chemistry 19 95 Reactions inorganic in liquid am- monia 16 19 Reactions unimolecular Arrhenius factors (frequency factors) in 14 133 Reactions of metal halides with alkyl cyanides 19 126 Rearrangement pinacol 14 357 340 CUMULATIVE INDEX 453 Rearrangement radical in gas-phase oxidation and related processes 18 243 Rearrangements aromatic 6 34 Rearrangements benzilic acid and related 14 221 Rearrangements photochemical and related transformations 15 393 Redox potentials of quinone relation of to chemical structure 4 94 Reduction by metal-amine solutions; applications in synthesis and deter- mination of structure 12 17 Reduction by metal-ammonia solu- tions of organic compounds 4 69 Relaxation processes molecular in liquids ultrasonic analysis of 11 134 Replacement reactions of co-ordina- tion compounds kinetics and mechanism of 16 3 16 Rhenium chemistry 15 372 Ring inversions the study of by nuclear magnetic resonance spectro- scopy 19,426 Salt hydrates crystal structures of 8 3 80 Salts basic structure of 1,247 Salts deposits of from oceans 1 91 Salts solid ionic conductance in 6 Sandmeyer reactions 6 358 Semiconductivity and catalysis 11,227 Semiconductivity of the phthalo- Sesquiterpenes synthesis of 18 270 Sesquiterpenoid chemistry 16 101 Sesquiterpenoids recent advances in chemistry of 11 189 Shock waves 14,46 Silicon acceptor properties of quadri- positive 17 382 Silicon chemistry of polymers con- taining 2 25 Silyl compounds 10 208 Sodium “flame” reactions 5 44 Solids molecular-sieve action of 3 293 Solids thermal transformations in 11 246 Solids transitions in 3 65 Solids separated by a narrow gap direct measurement of molecular attraction between 10 295 238 cyanines 18 113 Solution aqueous thermodynamics of ion association in 14,402 Solutions aqueous mechanism of electrode processes in 3 95 Solutions of non-electrolytes theories of 13.306 Solvation effects of on the properties of anions in dipolar aprotic solvents 16 163 Solvation ionic 3 173 Solvent extraction and its applications to inorganic analysis 5 200 Solvents ionising non-aqueous mc- tions in 10 451 Specificity in catalysis by metals 8 404 Spectra charge-transfer and related phenomena 8,422 Spectra charge-transfer theory of 15 191 Spectra electron-spin resonance of aromatic radicals and radical-ions 17 67 Spectra emission of flames 4 1 Spectra far ultraviolet ionisation potentials and their significance in chemistry 2 73 Spectra infrared and Raman of hydrocarbons. Part I acetylenes and olefins 6 1. Part 11 paraffins 7 19 Spectra infrared of heteroaromatic compounds 13 353 Spectra Raman of inorganic com- pounds 10 185 Spectra rotation.4 131 Spectra vibrational of ionic melts 17 225 Spectrophotometry fused-salt 19 349 Spectroscopy carbon-1 3 nuclear mag- Spectroscopy electron resonance of Spectroscopy far-infrared 17 362 Spectroscopy kinetic and flash photo- Stabilities of complex compounds 5 1 Stereochemistry of cyclohexane 7,221 Stereochemistry of elements of Sub- group VIB of the Periodic Table 10 407 Stereochemistry of elements of Group VIIl of the Periodic Table 3 321 Stereochemistry of inorganic com- pounds 11 339 netic resonance 19 144 free radicals 12 250 lysis 10 149 454 QUARTERLY REVIEWS Stereoregular addition polymerisa- Steric hindrance 2 107; 11 1 Steroidal alkaloids 7 231 Sterols steroids and terpenoids bio- genesis of.Part 1. Biogenesis of cholesterol and the fundamental steps in terpenoid biosynthesis. Part 2. Phytosterols terpenes and the physiologically active steroids 19 168 201 Strengths of organic bases prediction of 18 295 Structure of liquids in relation to their transport properties 14 236 Substituent interactions in ortho- substituted nitrobenzenes 18 389 Substitutions aroma tic nucleoph ilic mechanism and reactivity in 12 1 Sugar epoxides 13 30 Sulphur-fluorine bonds compounds containing 15 30 Sulphur nitride and its derivatives 10,437 Sulphuric acid behaviour of organic compounds in 8 40 Surface chemistry adsorption energy and adsorption equilibria 15 99 Surface compounds the chemistry of carbon-oxygen 13,287 Sydnones 11 15 Synthesis of sesquiterpenes 18,270 Synthetic gemstones 15 1 tion 16 361 Tautomerism of phenols 10 27 Technetium chemistry an outline of 16 299 Terpenes di- and tri- synthesis of 16 117 Tetronic acids 14 292 Theory of charge-transfer spectra 15 191 Thermochemical properties of phos- phorus compounds.17,204 Thermochemistry of the elements of Group IVB and IV comments on 7 103 Thermodynamics of ion association in aqueous solution 14 402 Thermodynamic properties estima- tion of for organic compounds and chemical reactions 9 229 Thermodynamic properties of high polymers and their molecular inter- pretation 1 265 Thermodynamic properties of organic oxygen compounds 15 125 Tin acceptor properties of quadri- positive 17 382 Topotactic reactions in inorganic oxy-compounds 16,343 Tracers radioactive preparation of 2 93 Transformation asymmetric and asymmetric induction 1 299 Transformations related and photo- chemical rearrangements 15 393 Transformations thermal in solids 11 246 Transition metals cyanide complexes of the.16 188 Transition-metal compounds crystal- line electron resistance in 14. 427 Transitions in solids and liquids 3 65 Transport control in heterogeneous reactions 6 157 Transport properties of Iiquids in relation to their structure 14 236 Triplet state 12 205 Triterpenes tetracyclic 9 328 Tropolones 5 99 Tryptophan biological degradation of 5 227 Ultrasonic analysis of molecular relaxation processes in liquids 11 134 Ultrasonic waves effects of on electrolytes and electrolytic pro- cesses 7 84 Vacuum microbalance techniques theory and applications of 19 231 Vapours of the elements 19,77 Veratrum alkaloids 12 34 Vibrational spectra of ionic melts 17 Wittig reaction 17.406 Wool wax constitution of 5 390 X-Ray crystal analysis modern methods of determination of mole- cular structure by and their ac- curacy 7,335 p-Xylylene chemistry of and of its analogues and polymers 12 301 225

ISSN:0009-2681    

DOI:10.1039/QR9651900441

出版商:RSC    

年代:1965

数据来源: RSC