New tetranuclear nickel(ll) cubane complexes of a heterodonor (NO) ligand: Synthesis, redox, spectroscopic and magnetic properties

Abstract

A new class of tetrameric cubane complexes of nickeh(ll) has been synthesised using bidentate 1,2- naphthoquinone 2-oxime ligand (HNqo, 1 ) at the peripheral site, and bridging methoxide and azide groups. Terminal solvent alcohol molecules complete the octahedral coordination around each metal centre. The four paramagnetic nickel (II) centres are electronically coupled in this geometrical arrangement (4). In dimethylefonnamide solution, four closely-spaced quasireversible nickel(III)-nickel(ll) redox couples are electrochemically observable by cyclic voltanunetry. These are compared with the oxidation behaviour of mononuclear octahedral nickel(Il) mixed complexes 3 and 4, where at least one N, O chelator is present. The results demonstrate the nonsupportive role of µ3-bridging groups towards sequential well defined electron transfer reactions in the electronically coupled cubane complexes of nickel(II).