Spin Exchange Coupling in Heterobimetallic MIIVIVO (M = Cu, Ni, Co, Fe, Mn) Macrocyclic Complexes. Synthesis, Structure, and Properties

A series of heterobimetallic complexes [(V IV O)L1Cu II (μ-OAC)(MeOH)](ClO 4 ) (1) and [(V IV O)L1M II (μ-OAc)(H 2 O)](ClO 4 )·H 2 O (M = Ni (2), Co (3), Fe (4), Mn (5)) derived from a symmetric tetraaminodiphenol macrocyclic ligand H 2 L1 have been synthesized and characterized. The crystal structure of 1 has been determined. The complex (C 27 H 41 N 4 O 10 ClCuV) crystallizes in the monoclinic space group P2 1 /c with a = 13.227(3) A, b = 14.932(3) A, c = 17.019(3) A, 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) A), while that of the vanadium by the oxo oxygen (V-O = 1.627(4) A). The metal centers are separated by 3.066(1) A, 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 IV O)L2Cu II (μ-OAc)(H 2 O)](ClO 4 ) (6) (where H 2 L2 is an asymmetric tetraaminodiphenol macrocyclic ligand) have been made and treated with the spin-Hamiltonian H = -2JS 1 ·S 2 . 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 II V IV O complexes.