Vibronic structure in the luminescence spectra of tetragonal d2 and d8 complexes analyzed by wavepacket dynamics on two-dimensional potential surfaces

The luminescence spectra of the tetragonal trans-ReO2(vinylimidazole)4+ complex and the square planar Pd(SCN)42? and Pt(SCN)42? complexes all show vibronic progressions in two predominant vibrational modes. In the first complex, the vibronic progressions involve high-frequency and low-frequency metal?ligand modes. In the square planar complexes, the two vibrational modes have similar frequencies. At the intermediate resolution, often observed experimentally, these compounds provide an example of the missing mode (or MIME) effect. Wavepacket dynamics on two-dimensional surfaces explain in a visual and intuitively appealing way the spectroscopic features. The distinct effects are caused by the different frequency ratios between the two modes of the two-dimensional models describing each complex. The emitting state structure determined from the spectra reveals similar changes along a bending normal coordinate for Pd(SCN)42? and Pt(SCN)42?