EPR AND ELECTROCHEMICAL STUDY OF NICKEL(III) COMPLEXES OF BIS(3,5-DICHLOROSALICYLALDEHYDE) ORTHO-PHENYLENEDIIMINE - EVIDENCE FOR ADDUCT FORMATION WITH PYRIDINES

Electrochemical oxidation of [bis(3,5-dichlorosalicylaldehyde) o-phenylenediiminato]nickel(II), [Ni(3,5-Cl2saloph)] (1), was performed in DMF and (CH3)2SO. In these strong donating solvents (S) the Ni(ll) complex is oxidized to a Ni(III) complex (low-spin d7 electron configuration), which can be formulated as [Ni(3,5-Cl2saloph)-S2]+. Upon addition by pyridines to freshly electrolyzed solutions of compound 1, novel electron paramagnetic resonance (EPR) spectra indicate the formation of new paramagnetic species, the species formed depending on the basic strength of the pyridines added. Thus, for the weaker bases, the EPR spectra indicate the presence of new Ni(lII) species (gav = 2.12) with the bases (B) coordinated axially ([Ni(3,5-Cl2saloph)-B2]+), whereas for the more strongly basic pyridines, the unpaired electron is transferred into the equatorial ligand, forming Ni(ll) ligand radical complexes (g = 2.00). The analysis of the EPR parameters of Ni(III)—pyridine adducts suggests that the adducts have a dz2 (2A1) ground state and also accounts for the observed g, values, in excess relative to that of the free electron, as being due to the influence of low lying quartet states. The application of the same model to the analysis of the spin Hamiltonian parameters of the EPR spectra of [Ni(3,5-Cl2saloph)-S2]+, shows that it has a dz2 ground state and yields values of E(dxz.dyz-dz2) in good agreement with those obtained from the electronic spectra. © 1990, American Chemical Society. All rights reserved.