Substituent effect on the coordination ability of the amide group of N-protected amino acids

The binary system Cu(II)-hydantoic acid (hydaH) and the corresponding ternary systems with 2,2'-bipyridine(bpy) and 1,10-phenanthroline (ophen) were investigated both in the solid state and solution. The crystal and molecular structure of the complex [Cu(ophen)(hyda)2].H2O was also determined. The crystal of the compound C18H20CuN6O7 is monoclinic, space group P2(1)/c, a = 7.601(5), b = 14.647(2), c = 19.714(3) angstrom, beta = 96.57(3), Z = 4, R = 0.049, R(w) = 0.053. The structure consists of discrete [Cu(ophen)(hyda)2] units and lattice water molecules. The Cu(II) atom is coordinated in the equatorial plane by two nitrogens from the ophen molecule and two oxygens from two hydantoate anions; the nitrogen atom of the neutral NH group of a hydantoate anion occupies the more distant fifth position (Cu-N(l) = 2.541(5) angstrom) giving rise to elongated square-pyramidal geometry. In solution the carboxylate species [CuL2] is formed in the binary system and the species [CuAL2], [CuAL(OH)] in the ternary systems with bpy and ophen. Spectroscopic data indicate that any possibility of the NH group being coordinated in solution can be excluded.