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That part of the field of single-crystal vibrational spectroscopy which is devoted to acquisition of well-proven assignments in terms of symmetry species is first placed within the wider context of solid state spectroscopy as a whole. Theoretical and practical factors which limit the size of crystal with which meaningful polarisation data can be obtained are then considered. Finally, brief summaries are given of selected areas of recent significant activity: chain and layer structures, silicates, and complexes with donor ligands.

A summary account is given of the phase transitions found at high pressure for several inorganic carbonyl and cyanide complexes: M(CO)6, (M = Cr, Mo, W); Re(CO)5Br; M2(CO)10, (M = Mn, Re) and MnRe(CO)10; Hg(CN)2; K2M(CN)4, (M = Zn, Cd, Hg); and K3Cu(CN)4. The structures of some of the phases have been deduced using group theoretical methods.

IR and Raman spectra of MCl2(meso-2,3-diaminobutane), (M = Pd, Pt), have been recorded down to liquid nitrogen temperature or lower. It is shown that correlation coupling occurs between closely spaced hydrogen-bonded pairs of molecules, which form a “super molecule,” but not between all eight molecules in the unit cell. The lattice mode region is also understood in outline on the basis of motions of the “super molecules” Methyl torsional modes appear to be near 140 cm−1.

Raman spectra of NaNO2 have been studied as a function of hydrostatic pressure to 40 kbar at 295 and 348 K. Slight changes in slope of mode frequency versus pressure plots support the view that a structural anomaly exists at 9 ± 1 kbar. The absence of qualitative changes in the Raman spectra allow the space group of NaNO2 IV to be specified as one of P1, P2, B2, Pm or Bm. The Raman spectrum of NaNO3 has been studied to 87 kbar. The changes observed are fully consistent with a second-order transition to a phase with symmetry C63v, as indicated by previous X-ray work, although the transition is sluggish.

The far-infrared spectra of platinum(IV) complexes of the types cis- and trans-[PtX4L2](X = Cl, Br, or I; L = donor ligand) are assigned and discussed. For the trans complexes the halogen-sensitive modes occur near those of the related [PtX4]2– species whilst the ν(Pt–X) pattern for the cis complexes covers a wide range which includes that of ν(Pt–X) in bridging situations in platinum(II) compounds. Assignments are given for ν(Pt–P), ν(Pt–As), ν(Pt–S), and for the associated bending modes.

Raman and far-i.r. spectra are reported and assigned for the solid complexes Cr(CO)3(π-arene)(arene = benzene, aniline, toluene, methyl benzoate, anisole, and hexamethylbenzene) and M(CO)3(π-mesitylene)(M = Cr, Mo, or W). For the benzene complex, discussion is based upon the factor group, but in the other cases the molecular point-symmetry proves to be an adequate approximation. C3v local symmetry is an inadequate approximation when discussing the skeletal modes of complexes of monsubstituted arenes.

Raman and i.r. spectra of the title compounds are reported and assigned for both solids and solutions. ν(C–H) modes show correlationsplitting, but the remainder of the internal modes of the π-allyl ligands can be discussed in terms of Cs local symmetry. ν(C–C–C) modes of the allyl skeleton are placed ca. 1383 and 1020 cm.–1 in the parent complex.

The O—H stretching frequency for methanol in the system methanol + dichloromethane + tetra-alkylammonium perchlorate is almost equal to that for a band which appears when perchlorate salts are dissolved only in methanol. The band is therefore assigned to methanol molecules hydrogen-bonded to perchlorate anions. A band which appears in the spectrum of HOD in H2O when perchlorates are added is, by analogy, similarly assigned. Other arguments against a previous theory that, for aqueous solutions, this band is due to free OD groups, are advanced. The influence of the cation upon the band for solvent molecules not associated with perchlorate ions is discussed.

The far-infrared spectra (70–400 cm.–1) of 36 thiourea and ethylenethiourea (imidazolidine-2-thione) complexes, embracing several different stereochemical types, are assigned and discussed. Metal–sulphur stretching frequencies, v(M–S), lie in the range 298–205 cm.–1 for the transition-metal complexes, and vary with co-ordination number and electron configuration in the manner now familiar from the behaviour of metal–hylogen stretching frequencies, v(M–X). For Group metals v(M–S) has been found as low as 170 cm.–1. The similarity between the spectra of thiourea complexes and those of thiocyanates has led to an assignment of the published data for thiocyanates. Some interesting variations in halogen-sensitive vibrations have been encountered.

I.r. spectra (70–4000 cm.–1) of nickel complexes of the type [Ni(S2C2R2)2]n–(R = H, CF3, or CN) and of [M(S2C2(CN)2)2]n–(M = Co, Cu, Zn, Pd, or Pt) are discussed. Vibrations containing a large (ν(M–S) contribution are found in the range 465–295 cm.–1. Frequency and intensity variations are consistent with the molecular orbital description of the bonding.For dithiophosphate complexes of three types of stereochemistry ν(M–S) is assigned in the region 330–220 cm.–1; the variation is mainly due to the differing masses of the metal.These results, together with other published work, lead to correlations for ν(M–S) for various ligands in the range 504–205 cm.–1.

The far-infrared spectra of some halogenocuprates of the types [CuX4]2–(planar and tetrahedral), [Cu2X6]2–, CsCuX3, and M2ICuCl4,2H2O have been studied. Complexes of the type CuX2L2(X = Cl or Br; L = donor ligand) are also considered. v(Cu–Cl) lies in the range 368—222 cm.–1 and v(Cu–Br) between 278 and 168 cm.–1. The spectra admit of a consistent interpretation without the need to postulate the presence of v(Cu–X) modes in the normal region due to stretching of copper–halogen “long” bonds. Bridging v(Cu–X) frequencies have been assigned but the range is severely overlapped by that of terminal v(Cu–X).

The ν(CO) spectra of Mo(CO)4 bipy (bipy = 2,2′-bipyridyl), cis-[W(CO)2{o-C6H4(PEt2)2}2],Cr(CO)3(π-mesitylene), and Cr(CO)3(π-C6H5·CO2Me) are examined in solution in n-hexane–chloroform or –nitrobenzene mixtures; the ν(NO) spectrum of Fe(NO)(S2CNMe2)2 is studied in benzene–nitromethane mixtures. Structure observed on the ν(CO) bands is discussed in terms of formation of solvent–solute complexes.

Raman and i.r. spectra are reported and assigned for X2Sn[Co(CO)4]2,X2Sn[Fe(CO)2(π-C5H5)]2(X = Cl, Br, and I), and M-SnCl3, (M = Mo(CO)3(π-C5H5); Rh(NBD)2; Ir(COD)2), and for a number of related compounds. Metal–metal stretching frequencies are in the range 165–235 cm.–1 and are intense in the Raman spectra.

Spectroscopic Properties of Inorganic and Organometallic Compounds provides a unique source of information on an important area of chemistry. Divided into sections mainly according to the particular spectroscopic technique used, coverage in each volume includes: NMR (with reference to stereochemistry, dynamic systems, paramagnetic complexes, solid state NMR and Groups 13-18); nuclear quadrupole resonance spectroscopy; vibrational spectroscopy of main group and transition element compounds and coordinated ligands; and electron diffraction. Reflecting the growing volume of published work in this field, researchers will find this Specialist Periodical Report an invaluable source of information on current methods and applications. Specialist Periodical Reports provide systematic and detailed review coverage in major areas of chemical research. Compiled by teams of leading experts in their specialist fields, this series is designed to help the chemistry community keep current with the latest developments in their field. Each volume in the series is published either annually or biennially and is a superb reference point for researchers. www.rsc.org/spr

Vibrational frequencies and force constants are reported for the ions [MCl6]2–(M = Ti, Zr, or Hf). An error in the early literature is corrected.

Raman and far-i.r. spectra for single crystals of tetrakis(thiourea)nickel(II) dichloride have been obtained at ca. 120 K and at ambient temperature. The results allow unambiguous assignment to A, B, and E species (in C4 symmetry). Descriptions of many of the internal modes are also offered.

Vibrational spectra of the ions [MCl6]2–(M = Cr, Mn, Fe, In, or lr) and [MCl6]3–(M = Mn or Ce) are assigned. The ν3 values show the effect of the differences in electronic structure of the metal atoms, being very low for M = Fe (t2g3eg2) and high for M = MnIII(Jahn–Teller distorted). Further spectra of tetrahalogenothallates are reported and show some differences at low frequencies from those previously published.

Far-infrared (60—4000 cm.–1) and laser-Raman spectra of solid complexes MI2[MCl6](M = Sn and Pb) are reported. Force constants are calculated on the basis of a modified Urey–Bradley force field and show a general decrease with increase in cation size. Some cation lattice modes are reported and found to decrease with increase in cation mass.

The far-infrared spectra (70–400 cm.–1) of tellurium tetrachloride show that its structure in the solid state differs from that in benzene solution, in which a molecular form is most probable. The solid bromide has a similar structure to the chloride.

An outline is given of an Algol computer programme for normal co-ordinate analysis. Some improvements in the force-constant refinement process are reported. The spectra of diborane, and of six halides of the formula M2X6(M = Al, Ga, or ln), have been analysed. In each case the force field is built up from the SVFF by adding interaction terms one by one, only those that are determined by the data being accepted. Force fields for all of the M2X6 molecules can be constructed by choosing 10 or more force constants from a set of 13; the force field for diborane differs considerably from these. A B–B force constant of 2·511 mdynes/A was found for diborane. In contrast, calculations for the M2X6 molecules became unstable when an M–M force constant was included, contrary to a previous report. An error in our previous calculations on auric chloride is corrected.

Copper(II) halides form complexes of the type CuX2L2(L is 2,3-diphenyl- and 2-methyl-quinoxaline) and CuX2L (L is 2,3-dimethylquinoxaline) with substituted quinoxaline. The 2,3-diphenylquinoxaline complexes appear to be monomeric whereas the others are polymeric. The 2-methylquinoxaline complexes have halide bridges and the 2,3-dimethyquinoxaline complexes are square-planar with organic ligand bridges. These structures are deduced from reflectance and far-infrared spectra and an examination of molecular models. Some copper(II) nitrate complexes of these ligands are described.

Partial or complete Raman and i.r. spectra are reported for WOCl4, WOBr4, MoO2Cl2, MoO2Br2, and WO2Cl2 as solids. A full assignment is given for WOCl4, and possible structures for the dioxide dihalides are discussed. A normal-co-ordinate analysis of WOCl4 is made.

A simple modification of the Bhagavantam–Venkatarayudu method is used to calculate the contribution of each atom in a unit cell to a representation of the factor group. Results have been computed for all sites in all 230 space groups, but only a few are given here in illustration of the method. The use of these data is illustrated for ionic, complex ionic, and molecular crystals as well as for polymers and layer structures. By its nature the method also yields the results of equivalent analyses for 32 of the point groups.

Raman spectra are reported for single crystals of the title compounds together with single-crystal i.r. reflectance data for the tetrakis-complex. The bis-complex is discussed on the basis of a factor-group analysis, but for the more complex unit cell of the tetrakis-complex a molecular model provides an adequate basis for assignment.

I.r. (and a few Raman) spectra are reporeted for the series M2I[MX5(H2O)], M2I[MX4(H2O)2], MX2,2H2O, and MX2,6H2O. From shifts in frequency with change of cation, metal, and halogen (X) the wagging mode of coordinated water is assigned at higher frequency than the rocking mode, contrary to currently accepted wisdom. Use of deuteriation has enabled identification of ν(Mâ†�OH2) and δ(M–O) modes in many cases. It is suggested that CoBr2,6H2O has the structure [CoBr2(H2O)4],2H2O and does not contain the hexa-aquo ion.

Raman and far-infrared spectra of solid halogenotellurates, M2I[TeX6], are reported and discussed. ν3 Is unusually broad and sometimes split, but the splitting is not different in origin from those shown by other [MX6]2– ions. It is concluded that there is no static distortion due to the lone pair but that the breadth of ν3 is associated with its presence in a symmetric orbital, as suggested by Urch. His description also accounts for the anomalous ratio of the bond-stretching force constants, K(Te–Br)/K(Te–Cl), which we find.

Infrared and partial Raman data are reported and assigned for the title compounds. A normal-co-ordinate analysis has been made for auric chloride. The most significant result of the calculation is that the bridge bond stretching force constant in auric chloride is 73% that of the terminal bond, whereas it is approximately 50% in aluminium chloride; this difference is rationalised and generalised.

The i.r.- and Raman-active fundamentals in the spectra of K2PtCl4 are unambiguously assigned from measurements on single crystals.

Single-crystal Raman spectra have enabled the identification and assignment to be made of nearly all the predicted factor-group fundamentals derived from internal modes of the anion in potassium chromate. Single-crystal i.r. and Raman methods were also used to study the lattice modes of this compound.

Nearly all the unit cell modes predicted by a factor-group analysis of tetrakis(thioacetamido)copper(I) chloride have been observed for single crystals in both Raman and i.r. spectra. The results show that the very simple i.r. spectrum of the Nujol mull is produced by the overlap of a large number of bands of different symmetry and similar frequency.

Single-crystal Raman spectra are reported and assigned for (NMe4)CdCl3, NH4CdCl3, (NH3Me)MnCl3, CsCuCl3, CsMnCl3,2H2O, and CsMnCl3,2D2O. Polarised far-i.r. studies have been made for (NMe4)CdCl3. Cscucl3, CsMnCl3,2H2O, and CsMnCl3,2D2O. With the exception of NH4CdCl3, which has a complicated double-chain structure, the results are discussed in terms of factor group analysis. Line group analysis suffices for NH4CdCl3.

The complexes Fe(CO)3L2, (L = Ph3P, Ph3As, Ph3Sb), react with mercuric halides to form 1 : 1 adducts; spectroscopic and conductivity evidence suggests their formulation as metal–donor complexes L2(CO)3Fe → HgX2. A 1 : 2 complex is formed by Fe(CO)3{(PhO)3P}2 and consists of a 1 : 1 compound plus a molecule of mercuric halide. Analogous structures are suggested for Fe(CO)5,nHgX2, (n= 1, 2).Features of the low-frequency spectra of the parent compounds and the adducts are discussed. Mercury–halogen frequencies are correlated with various structural situations.

Almost all the optically active modes of K2CuCl4(H2O)2 predicted by factor group analysis have been observed and assigned using single-crystal Raman and far-i.r. techniques. Less complete data are reported for K2CuCl4(D2O)2 and (NH4)2CuCl4(H2O)2. The spectrum of the trans-CuCl2(H2O)2 molecules present is strikingly similar to that reported for CuCl2,2H2O single crystals by Beattie, Gilson, and Ozin, showing that the effect of the ‘long-bonded’ interactions in both compounds is similar.

An assignment for the vibrational spectrum of the anion in K[PtCl3(NH3)],H2O is deduced from single-crystal Raman measurements. Evidence from Raman spectra of powder samples of K[PtCl3(ND3)],D2O and of both the protiated and deuteriated anhydrous materials (Cossa's salt) is also discussed.

IN a previous publication1 Adams and Gebbie reported the far-infra-red absorption spectra of some transition metal complex halides containing regular octahedral ions of the type MX6n−, X = halogen. We have now extended our observations to a series of halides of molybdenum and tungsten recently prepared by Edwards, Kennedy, Peacock and Said2.

Infrared and laser-Raman spectra of WF5Cl are reported and assigned on the basis of C4v symmetry. A tungsten–chlorine bond distance of 2·10 A is estimated from the P–R separation of ν1. This, and the high value of ν1, suggests the presence of some π-contribution to the W–Cl bond.

New Raman data for solutions, powders, and oriented single crystals are reported which allow a consistent assignment of the vibrational spectra of the title compounds. The four Raman-active ν(CO) modes for Mn2(CO)10 are at 2116(a1), 2024(e2), 1997(a1), and 1981(e3) cm–1. Low-frequency spectra of considerably improved quality are also presented. All of the a1 bands have been located for Re2(CO)10 and all but one for Mn2(CO)10 for solutions.

Infrared spectra have been obtained over the range 70–4000 cm.–1 for complexes of the types InX3L3 and InX3L2, where X = Cl, Br, and I and L = donor ligand. The evidence indicates a pentaco-ordinate monomeric structure for the InX3L2 series [L = Ph3PO, Ph3P, or ½(Ph2P·C2H4·PPh2)] in the solid state, the trans-octahedral form for InX3(dimethyl sulphoxide)3, and the cis-octahedral structure for InX3py3.

Far-infrared spectra (60–400 cm.–1) of the ions [M2X6]2–(M = Pd, Pt; X = Cl, Br, or I), are assigned. Normal-co-ordinate analyses have been made for the in-plane infrared-active modes. Bond-stretching force constants for the bridge bonds vary from 75 to 100% of those for terminal bonds.

The observation of Raman and far-i.r. spectra of oriented single crystals of [Et4N]2[InCl5] has enabled a probable assignment to be given for the anion.

Raman and i.r. spectra are reported and assigned for the compounds Mn2(CO)10, Mn(CO)5X (X = Cl or Br), and Hg[Mn(CO)5]2.

Far-i.r. reflectance spectra of M2IMCl6 complexes where M = Sn, Pt, or Te, have been used to estimate the half-bandwidths of the v3 vibration of the [MCl6]2– ions. The values are substantially lower than those found from absorption spectra of powdered samples but those for the tellurates are greater than those for the platinates and stannates. An earlier interpretation of the mull i.r. spectra is supported by these results.