The optical absorption spectra of the complexes IrCl62- and PtCl62- in single crystals of Cs2ZrCl6, Cs2HfCl6 and K2SnCl6, and PdCl62- in Cs2ZrCl6 have been studied at liquid helium temperature. Both molecular orbital theory and ligand field theory are used to interpret the results. The rich vibrational structure observed in many of the bands is analysed in terms of the vibrational modes of the complexes. Several long progressions involving up to twelve quanta of the totally symmetric vibration, ylg, were observed throughout the spectra, indicating that the transitions are to states in which the bond length has changed.

Luminescent bands due to transitions from the triplet states of the 5d6 configuration of Pt4+ in crystals of the type K2PtCl6 have been found in the red and green regions of the spectrum. A study of the temperature dependence of the band width of the red luminescence in K2PtCl6 powder has been made and fitted to a coth function. At liquid helium temperature both bands showed vibrational progressions, involving several quanta of the totally symmetric vibration.