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The linear vibronic coupling model has been applied to analyze the spectra of six transition metal complexes: [Pd(SCN) 4 ] 2− , [Pt(SCN) 4 ] 2− , [PdCl 4 ] 2− , [PtCl 4 ] 2− , [PdBr 4 ] 2− , and [PtBr 4 ] 2− . Time-dependent density functional theory (TD-DFT) is used to compute the vibronic parameters. We find that TD-DFT and the linear approximation enable one to understand the shape and structure of the electronic spectra of these molecules.

Luminescence spectra are reported for trans-[MoOCl(CN-t-Bu)(4)]BPh(4) and trans-[MoOF(pyridine)(4)]BPh(4). The maxima of the broad luminescence bands are at energies of 12000 and 13000 cm(-1), respectively. Resolved vibronic structure involves the metal-oxo stretching mode with a vibrational frequency of approximately 950 cm(-1) (Raman) in both compounds. The pressure behavior of the luminescence bands shows a distinct difference: a blue shift of +12 cm(-1) kbar(-1) is observed for [MoOCl(CN-t-Bu)(4)]BPh(4), and a red-shift of -8 cm(-1) kbar(-1) is obtained for [MoOF(pyridine)(4)]BPh(4). At pressures above 25 kbar, the luminescence maximum of [MoOCl(CN-t-Bu)(4)]BPh(4) shows a change from a blue-shift to a red-shift and the Raman peak corresponding to the metal-oxo stretching mode at 954 cm(-1) becomes broad and its maximum decreases with increasing pressure, leading to a strong deviation from the linear increase of +0.24 cm(-1) kbar(-1) observed at pressures below 25 kbar. These unusual pressure effects are rationalized in terms of the influence of pressure on the metal-ligand bonds and oxo-metal-ligand angles using DFT calculations.