Electronic structures of square-planar complexes

Electronic spectra of several square-planar complexes of the type (MXJZ (M = Pd(II), Pt(II), Au(II1); X = C1-, Br-, CN-, NHJ are reported in nonaqueous media at room and liquid nitrogen temperatures. In most cases the spectral resolution is considerably enhanced in the rigid, low-temperature glasses. Detailed assignments of spectra measured under carefully controlled conditions allow a comparison of electronic structures and energy levels in the various square-planar systems. The halide complexes show strong Iigand+metal charge-transfer absorptions, the cyanides show metakligand bands, whereas the ammine complexes exhibit allowed d + p tran- sitions. Trends in d-d and charge-transfer energies are discussed.