Crystallographic studies of metal peptide complexes. IV. (Glycyl-L-histidinato)copper(II) sesquihydrate

Glycyl-L-histidinato)copper(II) sesquihydrate crystallizes from solution at pH 6.5.The blue crystals are tetragonal, space-group P432~2, with a= 11.24+ 0.02, c= 17.84+ 0.04 A, Z= 8.The copper atom has coordination number 5. The four closest donor atoms, which have an approximately square arrangement abou the copper, are the amino-, peptide-and imidazole-1-nitrogen atoms of one peptide molecule and a carboxyl oxygen atom of another.The fifth donor atom, completing a square-pyramidal arrangement, is the oxygen of a water molecule.The copper also interacts weakly with the second oxygen atom of the carboxyl group to which it is bonded.The additional semi-molecule of water indicated by the composition of the complex lies on a twofold axis and participates in the hydrogenbond network.The structure was refined by full-matrix anisotropic least squares, the final reliability index R being 0"086 for the 1341 independent observed reflexions.