Crystal structure and magnetic properties of the alternating chain [Cu2(cdta)]·4H2O

Abstract

The crystal structure of the complex [Cu(OH₂)₄][Cu(cdta)](cdta = cyclohexane-1,2-diamine-NNN′N′-tetra-acetate) has been determined by X-ray methods. It crystallizes in the orthorhombic space group P2₁2₁2₁ with Z= 4 in a cell of dimensions a= 10.863(3), b= 12.074(4), and c= 14.802(6)Å. Least-squares refinement of 1 281 reflections [I > 2.5σ(I)] and 272 parameters gave a final R= 0.039. The complex exhibits a chain arrangement built up from alternating ‘hydrated’ and ‘chelated’ octahedral sites bridged by carboxylate groups. The ferrodistortive one-dimensional structural order observed arises from a co-operative Jahn–Teller effect between the two copper(II) co-ordination polyhedra. Magnetic susceptibility measurements, in the temperature range 4–50 K, are discussed in terms of a Heisenberg model involving alternating g values, the best yielding an antiferromagnetic exchange interaction of J=– 1.1 cm^–1. Such a value is consistent with the proposed exchange mechanism.