Spectroscopic and electrochemical studies of Ni-II, Cu-II, Pd-II and VOII complexes with naphthoquinonic ligands

The electron transfer complexes of general type [M(L(1))(2)], [M(L(2))(2)] and [M(L(3))(2)] with M = Ni-II, Cu-II, Pd-II and VOII ions have been investigated using 2-hydroxy-3-methylmercaptan-1,4-naphthoquinone (HL(1)), 2-amino-3-methylmercaptan-1,4-naphthoquinone (HL(2)) and 2,3-diamino-1,4-naphthoquinone (HL(3)) as ligands. Polarographic results confirmed that some the these neutral compounds underwent reversible or quasi-reversible one-electron reduction processes, and the reduction potentials for the [M(L(1))(2)] and [M(L(3))(2)] complexes were lower than those of the corresponding [M(L(2))(2)] complexes. EPR spectra of the prepared compounds, except the [Pd(L(2))(2)] complex, show that they are paramagnetic and some of them behave as free radicals stabilized through the cation. An attempt to correlate spectroscopic and redox parameters has been made. Copyright (C) 1996 Elsevier Science Ltd