Electronic band assignments of high- and low-spin Ni[R′2P(NR)2]2

Absorption spectra in the VIS and NIR region of the title compounds have been measured from KBr discs at temperatures down to 2 K. The paramagnetic complexes (R′=phenyl,R=ipropyl or methyl3Si) have pseudo-tetrahedral coordination in the crystal and the similar diamagnetic complex Ni[ipr2P(Nmethyl)2]2 is almost planar. All chelates have a small bite angle (76–78°). The electronic spectra are close to what is expected from distorted tetrahedral and quadratic Ni(II) complexes, respectively. Angular overlap model calculations, carried out using valence angles from the X-ray structure analysis, allow assignments of the measured peaks to electronic levels in D2d or D2 point symmetry. The model parameters obtained compare well with those of other NiN4 complex chromophores.