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Polarized infrared spectra of single crystals formed in a miniaturized high-pressure cell and the infrared and Raman spectra of polycrystalline films of CH2Cl2 and CH2Br2 have been measured. From their vibrational spectra it is suggested that the CH2Cl2 molecules occupy C2 sites in a hexagonal D3h crystal system and that the CH2Br2 molecules are on Cs sites in a hexagonal C6υ or D6h crystal system. Comparison of the vibrational spectra of the two methylene halides indicates that the intermolecular forces present in the solid phases of the two compounds have different origins. In CH2Cl2 there appears to be a considerable dipole–dipole contribution to the intermolecular forces. Conversely, in CH2Br2 atom–atom interactions (hydrogen–hydrogen repulsions) seem to account for the intermolecular forces. The Raman spectrum of a mixed crystalline sample of CH2Cl2 in an CH2Br2 lattice has been recorded in order to separately assign the components of bands due to the chlorine isotopes from those due to the factor-group splittings.

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Infrared and Raman spectra of solid samples of co-ordination compounds of formula trans-[MX, Y,] where M =Pd" and Pt'l, X = Ci, Br, and I, and Y = Me&, Me,Se, and Me,Te have been recorded over the frequency range 100-500 cm.-l. Assignments of fundamental modes to observed spectra are suggested. The frequencies of the vibrations of the relevant bonds suggest strongly that in bond order M-CI > M-Br > M-l and M-S > M-Se < M-Te.IN Parts I and I1 an account was given of the infrared and Raman spectra of solid samples of a series of platinum(I1) and palladium(11) di-and tetra-ammine complexes. It was concluded that the rigidity of the metal-ligand bond declined in the order M-C1 > M-Br > M-I. A careful analysis of the spectra of the dimethyl chalcogenides has been completed recently 374 and it seemed logical to prepare complexes of these ligands and to examine their vibration spectra. In this Paper, the low-frequency vibrations are reported and discussed with particular reference to the stretching vibrations of the metal-ligand bonds.A few reports are to be found in the literature in which vibrations of platinum-and palladium-to-sulphur, -selenium, or -tellurium bonds are discussed5-' but the only reports to be found on complexes containing dimethyl chalcogenides are those of Greenwood 8 and Lewis and their co-workers.