Crystal and molecular structure of D-histidino-L-histidinocobalt(II) dihydrate

Abstract

The structure of D-histidino-L-histidinocobalt(II) dihydrate, Co(C₆H₈N₃O₂)₂,2H₂O has been deterimined from three-dimensional X-ray diffraction data. The crystals are monoclinic with a= 10·04, b= 11·10, c= 15·31 Å, β= 111·6°, and space group P2₁/c. Positional and anisotropic thermal parameters were refined by least-squares methods; the final R for 2342 observed reflections is 0·11. The cobalt atom is octahedrally co-ordinated to the amino-nitrogen, an imidazole nitrogen, and an oxygen atom of each histidine group, at distances between 2·06 and 2·16 Å. One histidine group in the molecule is D and one L; the imidazole groups are cis to each other and the molecule has no symmetry. The two histidine groups differ in conformation, chiefly by a twist of 26° about the C_β–C_γbond, and this be attributed to their very different hydrogen-bounded environments.