OPTICAL-PROPERTIES OF NI[T-BU(2)P(O)NR](2) - A PARAMAGNETIC D(8) COMPLEX WITH PLANAR STRUCTURE

The origin of the triplet ground state in the recently synthesized par amagnetic, planar-coordinated complexes of nickel(II), Ni[t-bu(2)P(O)N R](2); R = i-propyl, c-hexyl, is ascribed to the small chelate bite an gle in these molecules. The nature of the singlet-tripler crossover in planar d(8) complexes is addressed as are the roles of the steric act ivity of the open d shell and of ligand-field stabilization energies i n 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-fiel d model.