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 T_N≈ 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 (E_1/2=+0.38 V vs. ferrocenium–ferrocene) corresponding to the couple Ni^IIINi^II–Ni^IINi^II and an irreversible oxidation wave at E_p^ox≈+1.04 vs. ferrocenium–ferrocene.