Synthesis and structural characterization of L-histidinato-D-penicillaminatochromium(III) monohydrate

Abstract

The novel chromium(III) amino-acid complex L-histidinato-D-penicillaminatochromium(III) monohydrate, [Cr(L-his)(D-pen)]·H₂O (his = histidine, pen = penicillamine), has been prepared by the reaction of D-penicillamine with an aqueous solution containing chromium(III) chloride (or nitrate) and L-histidine. The crystal structure of the complex has been determined from three-dimensional X-ray counter data. The complex crystallizes in the monoclinic space group P2₁, Z= 2, in a cell of dimensions a= 7.235(4), b= 12.150(8), c= 8.929(6)Å, β= 6.00(3)°. Full-matrix least-squares refinement of the structure. using 1 635 intensities, yielded a final R of 0.035. The complex is monomeric, the distorted octahedral geometry at the chromium giving rise to cis bond angles in the range 79.8(2)–102.2(2)°. The tridentate D-penlcillamine moiety co-ordinates as the dianion, being deprotonated at S and O, with Cr–S, Cr–N, and Cr–O bond lengths of 2.332(2), 2.094(5), and 1.989(4)Å, respectively. The histidine monoanion is also tridentate, co-ordlnating through N(amino), N(imidazole), and O, with associated chromium–ligand bond lengths of 2.063(4), 2.057(5), and 2.013(4)Å, respectively. The geometry of this complex is, therefore, quite similar to that found for the corresponding cobalt(III) complex: in both cases, the isomer isolated has S trans to O(his) and N(pen)trans to N(imidazole).