Ligand Field Theory of Ni(II) Complexes. III. Electronic Spectra and Solution Paramagnetism of Some Diamagnetic Ni(II) Complexes

Abstract

The observed electronic absorption spectra of six diamagnetic Ni chelates are successfully assigned using ligand field theory with consistent values of the field parameters. The observed solution paramagnetism of some of these diamagnetic chelates is attributed to an equilibrium between solvated molecules of the same symmetry in singlet and triplet states rather than to a change in symmetry of the complex as has previously been postulated. Calculations of the energies of six-coordinated Ni(II) complexes indicate that solution favors a triplet ground state for each symmetry studied. With this model, the extent of solvent-ion interaction determines the separation of singlet and triplet states and hence the distribution of molecules among these states. The proposed equilibrium mechanism and the calculated energy levels of the ion, used together in a consistent manner, give a quantitative explanation of both the paramagnetism and spectra of these complexes in solution.