The isomers of α-amino acids with copper(II). Part II. The crystal and molecular structure of cis-bis-[D-alaninato]copper(II)

Abstract

The crystal and molecular structure of a new crystalline modification of bis-[D-alaninato]copper(II), Cu(C₃H₆NO₂)₂′ has been determined from three-dimensional X-ray data. The new isomer crystallizes in the space group P2₁2₁2₁(D₂ ⁴) of the orthorhombic system, with Z= 4 in a unit cell of dimensions a= 11·63, b= 8·77, and c= 8·43 Å. 928 independent reflexions were estimated visually from Weissenberg and precession photographs and the structure was refined by least-squares methods to an unweighted R of 0·068. The inner co-ordination sphere around the copper atom is square pyramidal; the two bidentate α-amino acid rings are cis and form the basal plane of the pyramid, the apex being occupied by a carboxylate oxygen atom, from a neighbouring molecule, at a distance of 2·390(7)Å. The molecular structure is built up from parallel chains of molecules, polymerised in the c direction. The chains are formed from molecules joined through the apical bond, and are separated by repulsion between the copper atom and a methyl group in a neighbouring chain, which occupies the sixth position of a severely distorted octahedron around the copper atom at a Cu ⋯ C distance of 3·50(1)Å.