Crystal structures of N-benzenesulphonyl-DL-alanine and aqua-[N-benzenesulphonyl-DL-alaninato(2–)]copper(II) monohydrate: a model for metal ion–sulphonamide binding

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Abstract
The crystal structures of the title complex (1) and the ligand (2) have been determined and refined by full-matrix least squares to residuals of 0.050 (1 965 observed reflections) and 0.041 (1 585 observed reflections), respectively. Complex (1) crystallises in the space group P21/c with a= 13.533(1), b= 7.908(1), c= 12.066(1)Å, β= 111.04(1)°, and Z= 4, while the ligand crystallises in the space group P21/n with a= 5.251(1), b= 16.638(15), c= 12.628(1)Å, β= 99.19(3)°, and Z= 4. In complex (1), which is in a polymeric form, copper has an irregular stereochemistry. The alanine moiety forms a five-membered chelate ring in the equatorial square plane by co-ordinating through one of the carboxy-oxygens and the deprotonated nitrogen, the third and fourth corners of the square being occupied by a water oxygen and the ‘free’ carboxy-oxygen of a screw-related complex; one of the sulphonyl oxygens of a glide-related complex co-ordinates axially, while the oxygen from the chelate ring of the above screw-related complex co-ordinates in an off-axial direction. The co-ordinated water molecule is involved in an interligand hydrogen bond with the unco-ordinated sulphonyl oxygen, forming a six-membered water-bridged chelate ring. In packing, the complex (1) segregates into hydrophobic and hydrophilic regions with the water molecules forming a network of hydrogen bonds. The ligand (2) forms typical carboxylic acid hydrogen-bonded dimers which are linked by N–H O bonds. The major conformational change in the ligand, upon metal co-ordination, is a reorientation of the molecule about the C(carboxy)–Cα and Cα–N bonds to accommodate the metal ion.

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