Remarkably Intricate Raman Spectra of Platinum(II)–Ligand Skeletal Modes in Diamminedihalido Complexes

More than 100 calculations of vibrational frequencies for cis-[Pt­(NH3)2X2] (X = Cl–, Br–) and trans-[Pt­(NH3)2Cl2] have been published over the past 25 years. The high-quality Raman spectra presented here have sufficient resolution in the crucial region of metal–ligand modes to permit an assessment of frequency calculations. The peaks for symmetric and antisymmetric Pt–Cl stretching modes νs and νa are resolved in the 312–333 cm–1 region. Frequency variations due to 35Cl and 37Cl isotopes are shown to be comparable in size to the differences between νs and νa. Peaks corresponding to the two Pt–Br stretching frequencies are observed at 213 and 218 cm–1 and Pt–N stretching frequencies for all compounds between 485 and 540 cm–1. The crystal structures of trans-[Pt­(NH3)2Cl2] and cis-[Pt­(NH3)2Br2] at 300 and 120 K are reported and complement the variable-temperature vibrational frequencies.