Synthesis, structural and magnetic properties of macrocyclic aza-amido binuclear copper(II) complexes

Abstract

Binuclear, antiferromagnetically coupled, macrocyclic copper(II) complexes, [Cu₂(C₂₈H₃₂N₄O₄)]•H₂O (II) and [Cu₂(C₃₆H₃₂N₄O₄)]•CH₃CN•H₂O (III), involving asymmetric ligands with two deprotonated amide, two azomethine nitrogen, and two phenoxide donors at the binuclear centre, have been synthesized and characterized by single-crystal X-ray diffraction and variable temperature magnetic studies. Complex II crystallizes in the monoclinic system, space group P2₁/n, with a = 16.4854(9) Å, b = 7.6005(13) Å, c = 21.1617(11) Å, β = 104.090(5)°, Z = 4, R_f = 0.068 for 2062 significant reflections. The two copper(II) centres have square planar N₂O₂ donor sets with two phenoxide oxygen atoms bridging the copper centres with a copper-copper separation of 2.898(2) Å. A long copper-oxygen (amide) contact (2.808(10) Å) forms a weak dimer association. Complex III crystallizes in the triclinic system, space group P1^-, with a = 8.7771(9) Å, b = 12.3983(16) Å, c = 15.7299(16) Å, α = 85.003(11)°, ß = 84.574(8)°, γ = 76.838(10)°, Z = 2, R_f = 0.041 for 2966 significant reflections. The two copper(II) centres have distorted square-pyramidal geometry involving an N₂O₂ in plane donor set and two phenoxide oxygen bridges with a copper-copper separation of 3.018(1) Å. The fifth coordination site at each copper centre involves an amide oxygen from a neighbouring molecule (Cu(1)-O 2.371(4), Cu(2)-O 2.413(3) Å) in a staggered intermolecular array. Very strong antiferromagnetic exchange is observed in both cases (-2J = 689 ± 7 cm^-1 (II), -2J = 816 ± 8 cm^-1 (III)).