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

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Colm J. Campbell, Willem L. Driessen, Jan Reedijk, Wilberth Smeets and Anthony L. Spek


Abstract

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. [Cu2(glyim)2Cl2]·6H2O 1, [Cu2(glyim)2Br2]·5H2O 2, [Cu2(glyim)2Cl(H2O)][CF3SO3]·2H2O 3 and [Cu2(glyim)2Cl(H2O)][ClO4]·2H2O 4. The single crystal structure of 1 was determined. It consists of [Cu2(glyim)2Cl2] units and several, mostly disordered, water molecules. The ligands and the anions are grouped in dimers of formula [Cu2(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) Å. A well resolved EPR spectrum of 10–3M 3 in MeOH was obtained at 77 K with geff values for Hz1, Hxy1, Hz2 and Hxy2 at 2.69, 2.26, 1.89 and 1.86 respectively, an A|| 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 10–4M and lower the dinuclear signals break down and the complex decomposes into monomeric species (g|| = 2.27 and g = 2.10).


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