The crystal and molecular structures of the nickel(II) complexes of malonamide-derived unsubstituted 14-and 13-membered tetraazamacrocycles and NMR study of the complexes in aqueous solution

The crystal structures of the nickel(II) complexes of the 14- and 13-membered malonamide-derived macrocycles [NiL1]. 6H(2)O and [NiL2]. 5H(2)O (H2L1 = 1,4,8,11-tetraazacyclotetradecane-5,7-dione, H2L2=1,4,7,10-tetraazacyclotridecane- 11,13-dione) have been determined. Two deprotonated amide and two amine donors form the approximately square planar environment of the metal in both complexes. The averaged Ni-N-amide and Ni-N-amine bonds are longer in the complex of the 14-membered macrocycle as compared to the 13-membered one (1.889 vs. 1.839 Angstrom and 1.941 vs. 1.889 Angstrom for [NiL1] and [NiL2] respectively). Water molecules do not co-ordinate but form an extended network of hydrogen bonds in the crystal lattices. The ligand in [NiL1]. 6H(2)O has the N-meso and in [NiL2]. 5H(2)O the N-rac configuration of the secondary amino groups. The analysis of H-1 NMR spectra reveals that the solid state conformation of both the 14- and 13-membered co-ordinated ligands is retained in aqueous solution though a substantial amount of the N-meso isomer is also detected for the latter.