Dinuclear CuIIMII(M = Co, Ni, Cu or Zn) and CuIICuIcomplexes of a phenol-based dinucleating macrocycle with dissimilar N2O2and N2O2S sites

Abstract

A dinucleating macrocycle H2L with two 2,6-bis(iminomethyl)-4-methylphenolate entities combined through two lateral chains, CH2CH2 and CH2CH2SCH2CH2, at the imino nitrogens has been obtained as a mononuclear copper(II) complex [Cu(H2L)][CIO4]2. It reacted with a second metal ion under alkaline conditions to form dinuclear complexes [CuIIMIIL(NCS)2]·H2O (M = Co, Ni or Zn), [CuIICuIIL][CIO4]2 and [CuIICuIL]CIO4. The crystal structure of the dimethylformamide adduct, [CuZnL(NCS)2]·dmf, reveals the discrete CuZn dinuclear structure bridged by the two phenolic oxygens of (L)2–. The CuII resides at the site with the CH2CH2 lateral chain and assumes a square-pyramidal geometry together with an isothiocyanato nitrogen at the apex. The ZnII is at the site with the CH2CH2SCH2CH2 chain and assumes a similar square-pyramidal geometry with an isothiocyanato nitrogen at the apex. The sulfur on the lateral chain is not co-ordinated but disposed to the ZnII with the Zn ⋯ S separation of 3.48 A. An antiferromagnetic spin exchange operates in the CuIIMII(M = Co, Ni or Cu) complexes (J=–32 cm–1 for M = Co, –90 cm–1 for M = Ni and –440 cm–1 for M = Cu based on H=–2JS1S2). In cyclic voltammograms of [CuIICuIIL][CIO4]2 and [CuIICuIL]CIO4 the copper ion at the site with the CH2CH2SCH2CH2 lateral chain shows a reversible CuII–CuI redox couple at ≈+0.08 V (vs. saturated calomel electrode).