Crystal and molecular structure of sodium µ-(imidazol-1-yl-NN′)-bis-[(glycylglycinato-NN′O)cuprate(II)] hexahydrate: structure–magnetism relationship in imidazolate-bridged binuclear copper(II) complexes

Abstract

The structure of the title complex, Na[Cu₂(Gly-GlyO)₂(im)]·6H₂O [Gly-GlyO = glycylglycinate(2–), im = imidazolyl), has been determined from X-ray diffractometer data, to give final discrepancy indices of R= 0.0302, and R′= 0.0391. The complex crystallizes in the triclinic space group P with unit-cell dimensions a= 11.246(4), b= 10.464(3), c= 10.858(4)Å, α= 109.99(3), β= 115.05(3), γ= 85.05(3)°, and Z= 2. Each copper(II) atom has square-planar co-ordination by amino-nitrogen, deprotonated amide nitrogen, carboxylate oxygen of the glycylglycinate ligand, and by nitrogen of bridging imidazolate, to form altogether a binuclear copper(II) complex. The complex is almost planar and has an approximate two-fold axis which is coincident with that of the imidazolate ring. Variable-temperature magnetic susceptibility data measured down to 4.2 K show an antiferromagnetic exchange interaction with a coupling constant J=–19 cm^–1. The bridging imidazolate plane and copper(II) co-ordination planes make an angle of 5.8° for Cu(1) and 10.4° for Cu(2). The relative orientation of the bridging imidazolate and the copper(II) co-ordination planes does not seem to be responsible for the magnitude of the magnetic exchange coupling constant (J=–19 cm^–1) in this case. It is concluded that a π-exchange mechanism is not important in the imidazolate-bridged binuclear copper(II) complexes.