Spin exchange coupling in heterobimetallic M^IIV^IVO (M = Cu, Ni, Co, Fe, Mn) macrocyclic complexes. Synthesis, structure, and properties

Abstract

A series of heterobimetallic complexes [(V^IVO)L1Cu^II(μ-OAC)(MeOH)](ClO₄) (1) and [(V^IVO)L1M^II(μ-OAc)(H₂O)](ClO₄)·H₂O (M = Ni (2), Co (3), Fe (4), Mn (5)) derived from a symmetric tetraaminodiphenol macrocyclic ligand H₂L1 have been synthesized and characterized. The crystal structure of 1 has been determined. The complex (C₂₇H₄₁N₄O₁₀ClCuV) crystallizes in the monoclinic space group P2₁/c with a = 13.227(3) Å, b = 14.932(3) Å, c = 17.019(3) Å, β = 112.29(1)°, and Z = 4. Both the metal centers in 1 are six-coordinated and are triply bridged by the two phenolate and the acetate oxygens; the sixth coordination site of the copper atom is occupied by a distantly placed methanol oxygen (Cu-O = 2.452(5) Å), while that of the vanadium by the oxo oxygen (V-O = 1.627(4) Å). The metal centers are separated by 3.066(1) Å, and the dihedral angle (Δ) between the metal planes is 32.0°. Variable-temperature (4-300 K) magnetic susceptibility measurements of 1-5 and of [(V^IVO)L2Cu^II(μ-OAc)(H₂O)](ClO₄) (6) (where H₂L2 is an asymmetric tetraaminodiphenol macrocyclic ligand) have been made and treated with the spin-Hamiltonian H = -2JS₁·S₂. All the complexes, except 5, exhibit ferromagnetic exchange interaction with the following values of J (in cm^-1): 42.5 (1), 12.0 (2), 4.4 (3), 4.4 (4), and 46.0 (6); complex 5 behaves antiferromagnetically with J =-14.2 cm^-1. A linear correlation between J and Δ has been proposed for Cu^IIV^IVO complexes.