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(μ-HPO4-O)(μ-HPO4-O,O′)(μ-OH)]− · (H3O)+ · 6H2O (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) Å 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/kB = −3.7(1) K and using a molecular field approximation we estimated a weaker ferromagnetic interaction J′/kB ∼ 0.3 K between neighbour dinuclear units.

Graphical abstractThe synthesis, characterization and crystal structure of a novel dinuclear copper compound with l-arginine, mono and bidentate HPO42− oxoanions and an OH− anion are reported. The dinuclear character and bridging scheme, rare for metal–amino acid compounds, is attributed to the bonding characteristic of the phosphate anions. The magnetic properties and EPR spectra indicate an antiferromagnetic intradinuclear interaction J/kB = −3.7 K and a ferromagnetic coupling between these dinuclear units of J′/kB ∼ 0.3 K.Figure optionsDownload full-size imageDownload as PowerPoint slide