SYNTHESIS AND STRUCTURAL STUDIES ON 1 1 METAL-COMPLEXES WITH 1,3-DIMETHYLLUMAZINE AND 1,3,6,7-TETRAMETHYLLUMAZINE - CRYSTAL-STRUCTURE OF 2 DICHLORO COPPER(II) AND MERCURY(II) COMPOUNDS AND A POLYMERIC CHLORO-NITRATO BRIDGED-MERCURY(II) COMPLEX/

In absolute methanol medium, eight new 1:1 metal complexes of general formula (MX2L)-X-II . nH(2)O have been isolated (L = 1,3-dimethyllumaz ine (DLM) or 1,3,6,7-tetramethyllumazine (DLMD); M = Cu, Cd, Hg, Pd an d Pt; X = Cl- or NO3-). The experimental techniques used for their str uctural characterization were thermal (TG and DSC) and spectral method s (IR, C-13 and H-1-NMR and EPR) and magnetic measurements (77-290 K). Single-crystal X-ray diffraction studies have been performed on the c omplexes [CuCl2(DLMD)(H2O)]. H2O (1), [HgCl2(DLMD)] (2) and [HgCl(NO3) (DLMD)] (3). In all the complexes, the lumazine-derived ligands seem t o be coordinated in bidentate form through the N5 and O4 atoms. The co mplex 1 shows a monomeric five-coordinated structure in which the coor dination polyhedron can be best described as a trigonal bipyramid. The equatorial plane is occupied by two chlorine atoms (Cu-Cl 2.268 and 2 .261 Angstrom) and an oxygen O(4) from the organic ligand (Cu-O(4) 2.2 94 Angstrom), whereas the apical positions were designed by a coordina ted water molecule and the N(5) atom-of the bidentate pteridine ligand (Cu-O(1W) 1.950 Angstrom and Cu-N(5) 2.038 Angstrom). The crystal str ucture is conformed by an extense hydrogen bonds scheme in which the n on-coordinated water molecule plays an important role. In the compound 2, the pteridine ligand interacts only weakly with the Hg(II) ion (Hg -O(4) 2.772 Angstrom and Hg-N(5) 2.675 Angstrom); the structure must b e described as an adduct between the HgCl2 and the organic ligand in w hich the molecules of metallic salt retain their identity (Hg-Cl 2.284 and 2.288 Angstrom). These units are weakly paired through long inter actions;of each metal centre with chloride ions of a neighbour molecul e (Hg ... Cl 3.664 Angstrom). The mixed complex 3 displays a polymeric structure in which the nitrate groups act as bridging bifurcate ligan ds between two Hg(II) ions through only one of their three oxygen atom s. The coordination polyhedron around the Hg(II) ion must be described as a trigonal bipyramid in which the metal is surrounded by the O(4), O(1N) and O(1N') atoms in the equatorial plane at distances of 2.551. 2.563 and 2.618 Angstrom, respectively. In the axial positions, a ter minal chloride ligand (Hg-Cl(1) 2.307 Angstrom) and the N(5) atom of p teridine ligand (Hg-N(5) 2.208 Angstrom) can-be found. (C) 1998 Elsevi er Science Ltd. All rights reserved.