Synthesis, crystal structure and magnetic properties of a new dinuclear copper(II) amino acid complex [Cu2(L-arg)2(μ-HPO4-O)(μ-HPO4-O,O′)(μ-OH)]-•(H3O)+•(H2O)6

A novel dinuclear copper(II) complex with the amino acid L-arginine (L-arg), with mono and bidentate HPO42- oxoanions and an OH- anion. [CU2(L-arg)(2)(mu-HPO4-O)(mu-HPO4-O,O')(mu-OH)](-) center dot (H3O)(+) center dot 6H(2)O (1) was prepared and its structure was determined by X-ray diffraction methods. The two independent copper ions are in a distorted square pyramidal coordination, each bonded to one L-arginine molecule. These two CU(L-arg) units are bridged by two monoatomic equatorial-apical oxygen ligands belonging to a monodentate hydrogenphosphate group, and to the hydroxyl group. The copper ions in the dinuclear unit at d = 3.1948(8) angstrom are also connected by two equatorial oxygen belonging to a bidentate hydrogenphosphate. This dinuclear character and bridging scheme, not common for metal-amino acid compounds, is a consequence of the properties of the phosphate anions. The magnetic susceptibility at temperatures between 2 and 300 K and the isothermal magnetization curves at T = 2.29(1) K with applied fields up to 9 T were measured. The magnetic data indicate an antiferromagnetic intradinuclear exchange coupling J/k(B) = -3.7(1) K and using a molecular field approximation we estimated a weaker ferromagnetic, interaction J'/k(B) similar to 0.3 K between neighbour dinuclear units. (C) 2007 Elsevier Ltd. All rights reserved.