Synthesis of dinuclear metal complexes of a macrocyclic ligand with multi-ligating pendant-arms. Crystal structures of its manganese(II) and cadmium(II) complexes

Abstract

A series of dinuclear metal complexes, [M 2L](ClO 4) 2 (M=Mn 2+, Ni 2+, Zn 2+ and Cd 2+), of a pendant-arm macrocyclic ligand (H 2L) have been prepared via the cyclocondensation between sodium 2,6-diformyl-4-chlorophenolate and N-(2-methylenepyridinyl)tris(2-aminoethyl)amine and the subsequent transmetallation with metal perchlorates, and characterized spectroscopically. Among these, the crystal and molecular structures of [Mn 2L](ClO 4) 2 and [Cd 2L](ClO 4) 2 have been determined by X-ray diffraction. The structure of the manganese complex indicates that each pendant-arm is bonded bidentately to the adjacent metal atom and both arms are on the same side of the resulting tetra-imine macrocycle. The six-coordinated manganese ion has a distorted octahedral configuration in which an uncommon eight-membered chelating ring has been formed due to the non-bonding tertiary nitrogen. In the structure of the cadmium complex, the pendent arm binds in the same manner to the metal as in the manganese complex. Each metal atom is coordinated by all the donor atoms including the tertiary nitrogen atom in one chamber of the macrocycle, and the cadmium ion is seven-coordinated with a geometry of a highly distorted pentagonal bipyramid. The manganese(II) ions in the macrocycle are both essential high spin, with only a very weak antiferromagnetic interaction. The manganese compound showed only a moderate activity in the catalytic decomposition of hydrogen peroxide.