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Ranian and infrared spectra have been obtained for the tetrameric molecules [(CI-Is)3PtX]4 where X = OH, C1, and I. For the hydroxide and chloride, single-crystal Raman polarizations provide unambiguous determination of the symmetry species of the observed frequencies. Assignments to internal coordinates were made by intercomparisons of the spectra and comparisons with related molecules. Of particular interest is the observation in each case of a set of three strong low-frequency bands in the Raman spectrum, with frequency ratios close to those predicted for a tetrahedron of like atoms bound to one another in the "simple cluster" approximation. Normal-coordinate analyses were carried out using force fields containing a force constant for metal-metal interaction. Absolute Raman intensities were measured for the totally symmetric modes and used to calculate bond polarizability derivatives and estimate bond orders. The results indicate that bonds between the platinum atoms and the bridging X atoms are weak and highly ionic. The Raman intensities provide evidence for weak interaction between platinum atoms, which decreases with increasing internuclear distance along the series X = OH, C1, and I. The force constants for Pt-Pt stretching decrease in the same order but are much larger than expected in relation to the weakness of the Pt-Pt interaction. The bonding pattern is siniilar to that found previously for the oxygen-bridged complexes Bis(OH)126+, Pb4(0H)d4+, and T14(0C2Hj)a.

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