Copper (II) complexes of a macrocyclic binucleating ligand which exhibit two-electron oxidation and two-electron reduction. Structure of [Cu₂(C₂₄H₃₄N₄O₂)(CH₃OH)₂](ClO₄)₂, a macrocyclic dicopper(II) complex involving coordinated methanol

Abstract

The saturated ligand H₂L1, derived by template condensation of 4-methyl-2,6-diformylphenol and 1,3-diaminopropane, followed by borohydride reduction, generates binuclear, antiferromagnetically coupled, copper(II) complexes which exhibit cyclic voltammetry involving two one-electron oxidation steps (E_1/2 = 1.1 to 1.2 V, 1.3 to 1.4 V; Pt/CH₃CN/SCE) and two one-electron reduction steps (E_1/2 = −0.75 to −0.76 V, −0.89 to −0.90 V (GC/DMSO/SCE) with the formation of Cu(III)–Cu(III) and Cu(I)–Cu(I) and mixed oxidation state species. A trinuclear derivative, [Cu₂(L1)(CuCl₄)], appears to contain a spin-coupled binuclear species bound to a magnetically isolated tetrachlorocuprate(II) entity. The complex [Cu2(L1)(CH₃OH)2](ClO₄)2 forms brown crystals with a = 8.6516(7), b = 11.6832(9), c = 16.7205(6) Å, β = 92.596(5)°, P21/_n, Z = 2, R_f = 0.037 and has a copper–copper separation of 3.088(1) Å and two weakly bound trans-axial methanol molecules (Cu—O, 2.413(4) Å). Variable temperature magnetic studies on [Cu₂(L1)(ClO₄)₂] and [Cu₂(L1)](ClO₄)2 indicate strong antiferromagnetic exchange (−2J = 824 ± 5cm⁻¹, 827 ± 7cm⁻¹, respectively) in both cases.