SYNTHESIS, X-RAY STRUCTURE AND PROPERTIES OF A NEW NITRITE-BOUND COPPER(II) COMPLEX WITH 2-(3,5-DIMETHYLPYRAZOL-1-YLMETHYL)PYRIDINE IN A CUN4(O) COORDINATION

Synthesis and characterization of a nitrile-bound copper(II) compound [Cu(L-4)(2)(ONO)]ClO4 have been achieved (L-4 = 2-(3,5-dimethylpyrazol -1-ylmethyl)pyridine]. The bidentate ligand L-4 provides a pyridine an d a pyrazole donor site; however, they are separated by a methylene sp acer. The complex has been structurally characterized and it belongs t o only a handful of complexes having nitrito-bound mononuclear copper( II) centre. The metal atom has a distorted square pyramidal geometry w ith the copper atom displaced from the equatorial plane by 0.25 Angstr om. In MeCN solution the green complex exhibits a broad ligand-field t ransition at 655 nm with a shoulder at 675 nm and in dichloromethane-t oluene glass (80 K) it exhibits an EPR spectral feature characteristic of the unpaired electron in the d(x)2-(y)2 orbital Variable-temperatu re (80-300 K) magnetic susceptibility measurements in the solid stale as well as room temperature measurement in MeCN solution reveal mononu clear magnetically dilute copper(II) centre. When examined by cyclic v oltammetry (MeCN solution) it displays electrochemically irreversible Cu-II-Cu-I response [cathodic peak potential, E-pc (V vs saturated cal omel electrode (SCE)): -0.32]. An oxidative response is observed at 1. 14 V, probably due to bound-nitrite oxidation and is partially removed to generate a solvated complex at the electrode surface. The latter s pecies gives rise to a reversible Cu-II-Cu-I redox response [E-1/2 = 0 .41 V vs SCE]. (C) 1997 Elsevier Science Ltd.