Synthesis and structural studies on new M IIX 2L 2 dihalocomplexes of 1,3-dimethyllumazine and 1,3,6,7-tetramethyllumazine. Crystal structure of the monodimensionally hydrogen-bonded dichloro-bis (1,3-dimethylpteridine-2,4 (1H,3H)-dione-O 4,N 5) copper (II) dihydrate

Abstract

In order to understand the metal–pterin cofactor interactions in living systems, a number of complexes with general formula M IIX 2 (pteridine) 2AnH 2O have been obtained by reacting M IIX 2 (M=Ni, Cu, Cd and Pd ) and 1,3-dimethyllumazine (DLM) and 1,3,6,7-tetramethyllumazine (DLMD) (lumazine= (1 H,3 H)-pteridin-2,4-dione) in aqueous solution. These compounds have been characterized by means of analytical techniques (elemental analysis and TG), spectral methods (IR, 13 C and 1 H NMR, UV–VIS–NIR, EPR) and magnetic measurements (77–290 K). Single-crystal X-ray diffraction studies have been made on the complex [CuCl 2 (DLM) 2]·2H 2O. The metal ion occupies an inversion center and exhibits a distorted octahedral coordination. The coordination octahedron is elongated, the equatorial plane consists of two N(5) atoms of pteridine ligands and the two chlorine atoms; the two axial sites are occupied by the two O(4) atoms of the pteridine ligands. The monomeric unit is completed with two non-coordinated water molecules hydrogen-bonded to the chlorine ligands, making zig-zag chains parallel to the [110} direction in which the pteridine planes are roughly perpendicular to the c axis. The polymeric chains are linked to each other through Van der Waals interactions.