Investigation on coordination ability of N-chloro-acetylglycine towards Cu(II) in solid and solution state

Abstract

The solution and solid state behavior of the binary system Cu(II)- N-chloroacetylglycine (Cl-acglyH) and the corresponding ternary systems with 2,2′-bipyridine (bpy) and 1,10-phenanthroline (ophen) were investigated by means of pH-metric and spectrophotometric titrations. The X-ray crystal structure of the complex [Cu(ophen)(Cl-acgly) 2]·2H 2O (Cl-acgly = N-chloroacetylglycine monoanion) is also reported. The crystals of the compound C 20Cl 2CuN 4O 8H 22 are monoclinic, space group P2 1/ c, a = 17.574(3), b = 7.125(2), c = 25.113(6) Å, β = 130.04(2)°, Z = 4, R = 0.077, R w = 0.088. The structure consists of monomeric [Cu(ophen)(Clgly) 2] units and lattice water molecules. The Cu(II) atom is square planar coordinated by two carboxylic oxygens of two amino acid molecules and two nitrogen atoms of the ophen molecule. Two long contacts involve the uncoordinated carboxylic oxygens. Crystal packing is due to ring-stacking interaction involving ophen molecules and to a strong intramolecular hydrogen bond involving the chlorine atom and the amidic nitrogen of one ligand molecule. In solution the species [CuL 2] and [CuALOH] (A = bpy or ophen) prevail in the binary and ternary system, respectively, both arising from carboxylic-oxygen-metal coordination of the amino acid molecule. The coordination of the OH − group in the ternary species prevents metal hydrolysis up to pH 11. The possibility of forming hydrogen bond interactions involving the chlorine atom seems the to be determinant factor in stabilizing the ternary complexes.