Vibrational spectra of the hexafluoroplatinate ion PtF 62− and the question of dπ- dπ bonding in the hexachloro- and hexabromoplatinate ions

Abstract

The complete Raman spectrum of the PtF 6 2− ion is observed in an aqueous solution of the sodium salt, using excitation by the green mercury line 5461 Å. The spectrum does not show the intensity anomaly reported by woodward and creighton for the PtCl 6 2− and PtBr 6 2− ions, and attributed by them to the presence of the six t 2g d-electrons of the central transition-metal atom. It is suggested that the difference is due to the fact that the ligands Cl − and Br − (unlike F −) possess vacant d-orbitals and that these act as acceptors for the t 2 g d-electrons of the Pt atom forming d- d π-bonds in PtCl 6 2− and PtBr 6 2−. Support for this explanation is obtained from considerations of bond-stretching force constants. The infra-red absorption of the PtF 6 2− ion is studied in the CsBr and NaCl regions. The fundamentals ν 3 and ν 4 and a number of combination bands are observed.