Reductive and oxidative electrochemical study and spectroscopic properties of nickel(II) complexes with N2O2 Schiff bases derived from (±)-trans-N,N′-bis(salicylidene)-1,2-cyclohexanediamine

Abstract

Cyclic voltammetry, chronopotentiometry, chronocoulometry, controlled potential electrolysis and UV VIS were used in investigation of ligands and Ni(II) complexes with (±)-trans-N,N′-bis(salicylidene)-1,2-cyclohexanediamine substituted in orto- and/or para- positions of phenolate anions with tert-butyl and/or methoxy groups. Irreversible reduction and oxidation of ligands were shown. No influence of solvent on reduction of complexes, which results in Ni(I) complexes, was observed, however, an effect of solvent and substituents of phenolate anions on oxidation processes was proved. Anodic process in (CH3)2SO always results in appropriate Ni(III)-phenolate complex. Oxidation of orto- and para- substituted complexes in CH2Cl2 results in Ni(II)-mono-phenoxyl radicals, which undergo delocalisation and subsequently are oxidised to Ni(II)-bis-phenoxyl radicals. Last oxidation step of radicals produce long-lived Ni(II)-bis-phenoxonium cations. Complexes without substituents in para-and/or orto- position having formed Ni(II)-mono-phenoxyl radicals undergo dimerization. Mechanisms of electrode processes were studied and D and Ef values for processes of reduction and Ist step of oxidation of complexes were calculated.