Synthesis and characterization of new complexes formed between 1-methyllumazine and 1,6,7-trimethyllumazine ligand with transition metal(II) nitrate.: Crystal structure of cobalt(II), copper(II) and cadmium(II) complexes

The structures and spectroscopic properties of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) nitrate complexes of 1-methyllumazine (MLM) and 1,6,7-trimethyllumazine (MLMD) with general formula M(II)(NO3)(2)L-2.nH(2)O are reported. In all the complexes, the lumazine-derived ligands seem to be coordinated in bidentate form through the N5 and 04 atoms. The crystal structures of [Cu(MLM)(2)(H2O)(2)](NO3)(2) (1), [Co(MLMD)(2)(H2O)(2)](NO3)(2) (2) and [Cd(MLMD)(2)(NO3)(2)] (3) have been determined by X-ray crystallographic methods. In compounds I and 2 the nitrate anions are uncoordinated, and the metal ions are surrounded in an octahedral geometry by two bidentate lumazine ligands and two coordinated water molecules. The absolute configuration of the complex I can be described as the 4M stereoisomer, following Bailar's nomenclature, with the two lumazine in a cis arrangement and the complex 2 exhibits the 2L stereoisomer as is usually in this kind of complexes. Compound 3 consists of neutral mononuclear units, the Cd(II) environment being a bicapped octahedral close to the trigonal antiprism due to the two nitrate anions coordinating in a very unsymmetrical bidentate mode. (C) 2002 Elsevier Science B.V. All rights reserved.