Synthesis and structural studies on metal nitrate complexes with 1,3-dimethyllumazine and 1,3,6,7-tetramethyllumazine: crystal structure of two new cobalt(II) and copper(II) three-dimensionally hydrogen-bonded complexes and a cadmium(II) complex with unusual geometry

Abstract In absolute methanol medium, M II (NO 3 ) 2 (M = Co,Ni,Cu,Zn and Cd) react with 1,3-dimethyllumazine (DLM) and 1,3,6,7-tetramethyllumazine (DLMD) (lumazine = (1 H ,3 H )-pteridin-2,4-dione) to give complexes with general formula M II (NO 3 ) 2 (pteridine) 2 · n H 2 O. These compounds have been characterized by means of the analytical techniques (elemental analysis and thermogravimetry), 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 complexes [Co(DLM) 2 (H 2 O) 2 ](NO 3 ) 2 ·2H 2 O, [Cu(DLMD) 2 (H 2 O) 2 ](NO 3 ) 2 ·2H 2 O and [Cd(NO 3 ) 2 (DLMD) 2 ]. Cobalt and copper complexes crystallize in the monoclinic system (space group P 2 1 / n , Z = 2) with a = 8.746(1), b = 13.584(2), c = 10.997(1) A , β = 94.89(1)°, V = 1301.8(3) A 1 , and R = 0.057 for 3787 independent reflections with l >2 σ (1) and 202 parameters (Co/DLM complex) and a = 8.9929(7), b = 1.0574(9), c = 11.9242(7) A , β = 98.124(5)°, V = 1492.3(2) A 1 , and R = 0.039 for 2612 independent reflections with l >2 σ ( l ) and 230 parameters (Cu/DLMD complex). In both complexes, the metal ion occupies an inversion center and exhibits an octahedral coordination. The Co(II) coordination octahedron is tetragonally flattened, but the Cu(II) coordination is rhombically distorted. The equatorial plane consists of two N(5) and two O(4) atoms of pteridine ligands and the two axial sites are occupied by two oxygen atoms from the coordinated water molecules. The monomeric units together with non-coordinated water molecules and nitrate anions are involved in a complex three-dimensional H-bond network. The cadmium complex crystallizes in the monoclinic system (space group P 2 1 / c , Z = 2) with a = 8.5689(4), b = 18.5279(9), c = 8.6209(3) A , β = 106.894(3)°, V = 1309.6(1) A 3 , and R = 0.030 for 1260 independent reflections with l >2 σ ( l ) and 192 parameters. The structure consists of monomeric centrosymmetric units in which the cadmium atom is eight-coordinated by four nitrate oxygen atoms of two bidentate nitrate anions and two N(5)-O(4) lumazine bidentate ligands. The geometry of the coordination polyhedron could be described as an octahedron whose equatorial plane is formed by two bidentate N(5)-O(4) pteridine ligands and whose apical positions each seem to be split into two coordination positions occupied by bidentate nitrate ligands.