SYNTHESIS AND STRUCTURAL STUDIES ON METAL NITRATE COMPLEXES WITH 1,3-DIMETHYLLUMAZINE AND 1,3,6,7-TETRAMETHYLLUMAZINE - CRYSTAL-STRUCTURE OF 2 NEW COBALT(II) AND COPPER(II) 3-DIMENSIONALLY HYDROGEN-BONDED COMPLEXES AND A CADMIUM(II) COMPLEX WITH UNUSUAL GEOMETRY

In absolute methanol medium, M-II(NO3)(2) (M = CO, Ni, Cu, Zn and Cd) react with 1,3-dimethyllumazine (DLM) and 1,3,6,7-tetramethyllumazine (DLMD) (lumazine = ( 1H,3H)-pteridin-2,4-dione) to give complexes with general formula M-II(NO3)(2)(pteridine)(2) . nH(2)O. These compounds have been characterized by means of the analytical techniques (element al analysis and thermogravimetry), spectral methods (IR, C-13 and H-1 NMR, W-Vis-NIR, EPR) and magnetic measurements (77-290 K). Single-crys tal X-ray diffraction studies have been made on the complexes [Co(DLM) (2)(H2O)(2)] (NO3)(2) . 2H(2)O, [Cu(DLMD)(2)(H2O)(2)] (NO3)(2) . 2H(2) O and [Cd(NO3)(2)(DLMD)(2)]. Cobalt and copper complexes crystallize i n the monoclinic system (space group P2(1)/n, Z = 2) with a = 8.746(1) , b = 13.584(2), c = 10.997(1) Angstrom, beta = 94.89(1)degrees, V = 1 301.8(3) Angstrom(3), and R = 0.057 for 3787 independent reflections w ith I > 2 sigma(I) and 202 parameters (Co/DLM complex) and a = 8.9929( 7), b = 14.0574(9), c = 11.9242(7) Angstrom, beta = 98.124(5)degrees V = 1492.3(2) Angstrom(3), and R = 0.039 for 2612 independent reflectio ns with I>2 sigma(I) and 230 parameters (Cu/DLMD complex). In both com plexes, the metal ion occupies an inversion center and exhibits an oct ahedral coordination. The Co(II) coordination octahedron is tetragonal ly flattened, but the Cu(II) coordination is rhombically distorted. Th e equatorial plane consists of two N(5) and two O(4) atoms of pteridin e ligands and the two axial sites are occupied by two oxygen atoms fro m the coordinated water molecules. The monomeric units together with n on-coordinated water molecules and nitrate anions are involved ln a co mplex three-dimensional I-I-bond network. The cadmium complex crystall izes in the monoclinic system (space group P2(1)/c, Z = 2) with a = 8. 5689(4), b = 18.5279(9), c = 8.6209(3) Angstrom, beta = 106.894(3)degr ees, V = 1309.6(1) Angstrom(3), and R = 0.030 for 1260 independent ref lections with I > 2 sigma(I) and 192 parameters. The structure consist s of monomeric centrosymmetric units in which the cadmium atom is eigh t-coordinated by four nitrate oxygen atoms of two bidentate nitrate an ions and two N(5)-O(4) lumazine bidentate ligands. The geometry of the coordination polyhedron could be described as an octahedron whose equ atorial plane is formed by two bidentate N(5)-O(4) pteridine ligands a nd whose apical positions each seem to be split into two coordination positions occupied by bidentate nitrate ligands. (C) 1998 Elsevier Sci ence S.A. All rights reserved.