Dinuclear CuIIMII(M = Co, Ni, Cu or Zn) and CuIICuI complexes of a phenol-based dinucleating macrocycle with dissimilar N2O2 and 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 [Cu^IIM^IIL(NCS)₂]·H₂O (M = Co, Ni or Zn), [Cu^IICu^IIL][CIO₄]₂ and [Cu^IICu^IL]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 Cu^II resides at the site with the CH₂CH₂ lateral chain and assumes a square-pyramidal geometry together with an isothiocyanato nitrogen at the apex. The Zn^II 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 Zn^II with the Zn ⋯ S separation of 3.48 Å. An antiferromagnetic spin exchange operates in the Cu^IIM^II(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 [Cu^IICu^IIL][CIO₄]₂ and [Cu^IICu^IL]CIO₄ the copper ion at the site with the CH₂CH₂SCH₂CH₂ lateral chain shows a reversible Cu^II–Cu^I redox couple at ≈+0.08 V (vs. saturated calomel electrode).