Tetra-co-ordination of nickel (II)–III visible and ultra-violet absorption spectra of NiX2·2PR3 complexes

Visible and ultra-violet absorption spectra have been taken for complexes of the type NiX2·2PR3 (X = NCS, Cl, Br; R = n-propyl, i-propyl, s-butyl, cyclohexyl). An assignment of the various transitions is suggested. Frequency shifts depending on alkyl substitution are shown to be due either to steric effects or to non-bonded group perturbations.