Synthesis, magnetic properties, redox behaviour, and crystal structure of the bridged binuclear nickel(II) complex [Ni2(µ-OH)(µ-CH3CO2)2L2]ClO4·H2O

Abstract

Reaction of Ni(CH3CO2)2·4H2O with N,N′,N″-trimethyl-1,4,7-triazacyclononane(L) in methanol and addition of solid NaClO4·H2O yielded a blue-green binuclear nickel(II) complex containing a hydroxo and two acetate groups as bridging ligands. The crystal and molecular structure of the compound has been established by X-ray diffraction. It consists of binuclear cations [LNi(µ-OH)(µ-CH3CO2)2NiL]+, unco-ordinated perchlorate anions, and water of crystallization. Variable temperature (4–300 K) magnetic susceptibility measurements show a weak antiferromagnetic exchange coupling (J=–4.5 cm–1, 〈g〉= 2.17) between nickel centres with TN≈ 7.1 K. The electronic spectra, measured both in the solid state and in solution, yielded the Racah parameter B(873 cm–1) and the spin–orbit coupling constant λ(–208 cm–1). The cyclic voltammogram of the compound in acetonitrile revealed a quasi reversible one-electron transfer (E1/2=+0.38 V vs. ferrocenium–ferrocene) corresponding to the couple NiIIINiII–NiIINiII and an irreversible oxidation wave at Epox≈+1.04 vs. ferrocenium–ferrocene.