Dinuclear Cu^IIM^II (M = Co, Ni, Cu or Zn) and Cu ^IICu^I complexes of a phenol-based dinucleating macrocycle with dissimilar N₂O₂ and N₂O₂S sites

A dinucleating macrocycle H₂L with two 2,6-bis(iminomethyl)-4- methylphenolate entities combined through two lateral chains, CH ₂CH₂ and CH₂CH₂SCH ₂CH₂, at the imino nitrogens has been obtained as a mononuclear copper(II) complex [Cu(H₂L)][ClO₄] 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][ClO₄]₂ and [Cu^IICu ^IL]ClO₄. 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 CH ₂CH₂SCH₂CH₂ 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][ClO₄]₂ and [Cu ^IICu^IL]ClO₄ 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).