Glycine coupled to a bis(imidazole): a tetradentate ligand rendering dinuclear copper(II) compounds through ligand sharing

摘要

The tetradentate ligand (carboxymethylamino)bis(imidazole-2-yl)methane (Hglyim), obtained through the reaction of glycine with bis(imidazol-2-yl)nitromethane, rendered several dinuclear copper(II) compounds, viz. [Cu-2(glyim)(2)Cl-2]. 6H(2)O 1, [Cu-2(glyim)(2)Br-2]. 5H(2)O 2, [Cu-2(glyim)(2)Cl(H2O)][CF3SO3]. 2H(2)O 3 and [Cu-2(glyim)(2)Cl(H2O)][ClO4]. 2H(2)O 4. The single crystal structure of 1 was determined. It consists of [Cu-2(glyim)(2)Cl-2] units and several, mostly disordered, water molecules. The ligands and the anions are grouped in dimers of formula [Cu-2(glyim(-))(2)(Cl-)(2)] in which the two copper(II) ions are entangled by two ligands. Each copper is in a square pyramidal N3OCl environment with the chloride ion occupying the apical position. Two of the co-ordinating nitrogens are from the imidazole groups of one ligand, while an amine nitrogen and a carboxyl oxygen are donated by the other ligand. This 2+2 ligand-sharing arrangement imposes a rather short distance on the two copper(II) ions, i.e. 3.249(2), 3.357(2) and 3.373(2) Angstrom. A well resolved EPR spectrum of 10(-3) M 3 in MeOH was obtained at 77 K with g(eff) values for H-z1, H-xy1, H-z2 and H-xy2 at 2.69, 2.26, 1.89 and 1.86 respectively, an A(parallel to) value of 87 G and a half-field signal at g = 4.24, indicating the preservation of the dinuclearity in solution (D = 0.047 cm(-1)). At concentrations of 10(-4) M and lower the dinuclear signals break down and the complex decomposes into monomeric species (g(parallel to) = 2.27 and g(perpendicular to) = 2.10). [References: 19]