Comment on “optical properties of Ni[t-bu2P(O)NR]2. A paramagnetic d8 complex with planar structure”

The origin of the triplet ground state in the recently synthesized paramagnetic, planar-coordinated complexes of nickel(II), Ni[t-bu2P(O)NR]2; R = i-propyl, c-hexyl, is ascribed to the small chelate bite angle in these molecules. The nature of the singlet-triplet crossover in planar d8 complexes is addressed as are the roles of the steric activity of the open d shell and of ligand-field stabilization energies in achieving it. The paramagnetic moment and its temperature variation for the green form of the c-hexyl derivative are reproduced, together with the reported electronic spectrum, within the cellular ligand-field model.