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 (E1/2 = 1.1 to 1.2 V, 1.3 to 1.4 V; Pt/CH3CN/SCE) and two one-electron reduction steps (E1/2 = −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, Rf = 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.