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Raman spectra of Mn2(CO)10 and Re2(CO)10 have been studied to 27 and 98 kbar respectively, and the infrared (IR) spectrum of Re2(CO)10 to 30 kbar at ambient temperature. Both materials undergo a first-order structural phase transition at high pressure (Mn at approximately 8 kbar, Re at approximately 5 kbar) which is accompanied by dramatic changes in all regions of their vibrational spectra. These data are interpreted in terms of a change of molecular geometry from D4d to D4h. In the new high-pressure phases the M to carbonyl backbonding is increased significantly for the axial but not the equatorial carbonyls. The molecular torsion is implicated in the phase change but is not thought to drive it.

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.

Phase transitions have been observed in mercury (II) cyanide near 2.5, 89, 19 and 60 kbar. The I/II transition appears to be of second order with the structure of phase II closely related to that of the parent molecular type. Using Landau theory, three possible structures have been identified for the new phase II, of which S24 is marginally better in accord with the evidence. A major reconstruction of the lattice occurs at the II/III transition; the coordination number of mercury appears to increase to four, and the structure becomes covalently bonded, rather than molecular. Phase IV has a spectrum consistent with it having the cubic anti-cuprite structure adopted at STP by Zn(CN)2 and Cd(CN)2. Above 60 kbar, brown polymeric Hg(CN)2V is formed irreversibly. It has a single IR absorption

Raman spectra of CH3Hg (X=Cl,Br,I) have been studied as a function of pressure using diamond anvil cells. Phase transitions were discovered in the chloride at 1.5+or-0.3 and 5.9 kbar, with an almost immediate further transition near 6 kbar to a phase stable to at least 40 kbar. CH3HgBr shows a single transition at 12.5 kbar. Soft modes were found for all three materials. That for the bromide was followed by change of temperature as well as of pressure. The crystal structure of CH3HgBr was found to be like that of the chloride, but of a different space group (P421m, Z=4), allowing slight nonlinearity of the C-Hg-Br skeleton. On the basis of this structural evidence a phase diagram is proposed. A very narrow (about 0.1 kbar) phase in CH3HgCl may be incommensurate. Preliminary studies of CH3HgI show that its behaviour parallels that of its congeners, but that the crystallography is different in detail.

Infrared reflectance spectra are reported for oriented single crystals of MAMC and PAMC with the electric vector parallel to the anionic sheets for temperatures from 50 to 295K. Single-crystal Raman spectra were also obtained at similar temperatures. The main features of the spectra, particularly for the ambient temperature phases, are assigned with the aid of a factor group analysis. This phase for MAMC, although orthorhombic, behaves spectroscopically as pseudo-tetragonal, but PAMC is plainly orthorhombic. Modes above 260 cm-1 are attributed to cation internal modes, including torsions. The phase III (tetragonal) to phase IV (monoclinic) transition is distinguished in the Raman spectra by disappearance of an intense broad features at about 35 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.

Raman spectra have been obtained for HgCl2 to 145 kbar and HgBr2 to 100 kbar and phonon pressure dependencies established. The phase transition in HgCl2 said to be at 6.5 kbar, on NQR evidence, has been located at 2.2 kbar. A new first-order phase change has been found in HgCl2 at 79.0 kbar. Also in HgCl2, there are two bands that pressure scan differentially such that one overtakes the other, but they do not appear to be in resonance. Improved values for the phase transitions in HgBr2 are 4.0, 26.0 and 41.0 kbar. It is suggested that there are no structural equivalences between the two series of four polymorphs based upon the chloride and bromide respectively.

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.

A new design of diamond anvil high pressure cell suitable for use in infrared and Raman spectroscopy is described. Its performance is demonstrated with particular reference to the pressure dependence of the infrared spectrum of K2PtCl6 and the Raman spectrum of W(CO)6. In contrast to earlier reports, in which forward scattering geometry was used, this design of cell is shown to be very suitable for Raman use in the 180° excitation mode. However, severe limitations are imposed by the fluorescence emission of diamond and of sapphire. Conditions under which the cell can be used for Raman work are summarized. New fluorescence and Raman features are reported for diamond. In particular, a band at 1730 cm−1 is characteristic of type I stones and may be due to C to N bond stretching at defect centers.

Raman single-crystal spectra are reported for eight hydrates and deuteriates [MCl5(H2O)]2–(M = In or Fe). Many fewer lattice modes were found than predicted, but for the anion internal modes factor-group predictions accord well with observation. A complete assignment in terms of anion C4v symmetry is deduced. Deuteriation enabled identification of all skeletal modes associated with oxygen-atom motions. The most unusual feature of the assignments is that π(MCl4) modes come above δ(MCl4) modes. Comparison with single-crystal assignments for [InCl5]2– show that the largest change is in the A1π(InCl4) mode which is raised upon aquation of the complex.

Diamonds intended for use as anvils in high-pressure devices for Raman and infrared spectroscopy must be selected carefully. For Raman use it is suggested that a useful criterion is whether or not the second-order spectrum of diamond can be seen above the accompanying fluorescence. Some type IIa stones are also suitable for Raman use and are superior to IIb stones in the infrared region above 2000 cm-1.

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.

All the Raman-active modes of [Fe(CN6)]3– have been observed in aqueous solution. For single-crystals (ambient and ca. 160 K) the predictions of factor-group analysis are largely borne out by experiment, as is most of the Raman spectrum calculated by Nakagawa and Shimanouchi. Bonding in the crystal is discussed.

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.

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.

Raman spectra of hexamethylenetetramine and several substituted benzophenones have been studied in situ on thin layer chromatography plates. Success depends upon the nature of the substrate (Kieselgel HR was the best found), the eluant, the retention factor, fluorescence of both plate and sample, and the scattering efficiency of the sample itself. It is concluded that the method is viable within the restrictions discussed, but that an instrument with rapid spectrum accumulation facilities would be necessary for routine analytical application.

The complex Raman and i.r. spectra of ruthenocene at ambient and liquid-nitrogen temperatures have been interpreted with the aid of solution and Raman single-crystal data to yield a complete assignment, including inactive modes. The polarisation property of the π(C–H) modes in ferrocene has been determined for the first time. Contrary to the accepted order, the i.r.-active ring ‘tilt’ mode of ruthenocene comes at lower frequency than the M–ring bond stretch.

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.

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.

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.

The long-sought ν4(a1′) mode of (PNCl2)3 has been located at 172 cm–1 in solution and its symmetry species confirmed by a Raman Study of an oriented single crystal. Experimental evidence from the crystal spectra also allowed distinction between e′ and e″ species. A reassignment of the spectrum is offered.

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.

New Raman spectroscopic evidence for solutions and oriented single crystals is presented from which a reassignment is made for the ν(CO) frequencies of the title compounds.

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.

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.

A detailed Raman study of the title compounds, together with new far-i.r. data, has permitted a more complete assignment than previously available.