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Far-i.r. spectra of A2[PdCl4] and A2[PtCl4](A = K, NH4, or ND4) have been investigated at temperatures below 100 K for the first time. Several new bands occur in the 200–360 cm–1 region on cooling to ca. 20 K. These and other features are discussed with the aid of single-crystal polarised-transmission measurements on [NH4]2[MCl4](M = Pd or Pt) in the range 60–180 cm–1, which yield evidence for the positions of the translatory modes. A theoretical analysis is given of the space groups to which these solids might transform at low temperatures. Among the structural possibilities considered are out-of-plane distortions of the anions.

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.

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.

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.

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