Ligand Field Theory of Ni(II) Complexes. I. Electronic Energies and Singlet Ground-State Conditions of Ni(II) Complexes of Different Symmetries

Abstract

A parametric method of calculating the electronic energies of an ion of configuration 3d⁸ (3d² positrons) when placed in a ligand field of point charges or dipoles is described. The method is applicable with a change of sign of the energy matrix elements to ions with a 3d² electronic configuration. By use of the experimentally determined free ion term energies for the Ni(II) ion the calculations are made specific. The final energy eigenvalues obtained here are for the Ni(II) ion in four and six coordinated complexes of tetragonal, octahedral, cis‐, and trans‐planar symmetries. All free ion states of the same multiplicity and symmetry arising from the ground‐state configuration were allowed to interact. An effective interelectron distance, dipole moment, and point charge were used as parameters. Some of the numerical results for specific values of the parameters are given as examples. The remainder of the energy calculations are tabulated in the dissertation. Minimum field strength conditions necessary for a four coordinated complex to become diamagnetic are determined using the calculated energies. The relative ease of conversion to a singlet ground state in the different symmetries is noted and the effect of an axial field on the change in multiplicity is obtained from the results of the calculations for the six‐coordinated complexes. The results will also be used subsequently to assign the low intensity electronic spectra obtained for a series of Ni(II) chelates of appropriate symmetries and to explain the effect of solvent on the spectra and magnetic moments of these chelates.