OXALATE-BRIDGED DINUCLEAR NICKEL AZACYCLAM MACROCYCLIC COMPLEXES - SYNTHESIS AND ELECTROCHEMICAL STUDY

New dinuclear nickel(II) complexes of formula [(NiL)(2)ox](ClO4)(2) (o x(2-)-oxalate anion, L = 3-methyl-1,3,5,8,12-pentaazacyclotetradecane, complex 1; L = droxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane, com plex 2; and L = 1,4,8,11-tetraazaundecane, complex 3 have been synthes ized and characterized by means of absorption and IR spectroscopy. Ele ctrochemical studies of 1-3 in DMF and DMSO indicated high stability o f the mixed-valence species (Ni-II-Ni-III). The values of K-com and De lta G(com) of the comproportionation equilibrium (Ni-II-Ni-III) + (Ni- III-Ni-III) = 2(Ni-II-Ni-III), were determined by cyclic voltammetry, and compared with those for the complex [(NiL4)(2)ox](2+) (L-4 = 1,4,8 ,11-tetraazacyclotetradecane, cyclam). The main factor contributing to the stabilization of the mixed-valence state was ascribed to the elec tronic delocalization through the bridging oxalate ligand. The influen ce of the structure of amine ligands on the values of K-com was discus sed. The electrochemical behaviour of dinuclear complexes was compared with that of the parent mono-valent species. Polynuclear transition m etal complexes represent an interesting class of coordination compound s which often display intriguing spectroscopic, magnetic and electroch emical properties. Such compounds attract much attention because of th eir functions associated with metal-metal interactions [1] and as mode ls for metal biosites [2]. The complexes of linear and macrocyclic pol yamines serve as convenient building blocks for the construction of su ch polynuclear tin the simplest case dinuclear) aggregates. These comp ounds possess very high thermodynamic stability, kinetic inertness and the ability to change easily the oxidation state of the coordinated m etal ions.(C) 1998 Elsevier Science S.A. All rights reserved.