Copper(II) Azido Complexes: Synthesis, X-ray structures, thermal and magnetic properties

Licentiate thesis, 2009

This thesis focuses on the synthesis and X-ray structure analysis of seven copper(II) and one cobalt(II) azido coordination polymer with quinoline and pyrazine derivatives as bridging co-ligands. The synthesis of these complexes were done by direct mixing of the metal salt (Cu(NO3)2 and CoCl2) and the organic ligand (pyrazinecarbonitrile, quinoxaline, quinoline-4-carboxylic acid and 2,5-dimethylpyrazine) solutions followed by the dropwise addition of aqueous sodium azide (NaN3) with continuous stirring. Crystals were obtained upon slow evaporation of the resulting clear solutions. X-ray crystal structure analysis revealed four monomeric Cu(II) pyrazinetetrazolate structures: [Cu(pyzt)2H2O] (1), [Cu(pyzt)2(H2O)2] (2), [Co(pyzt)2(H2O)2] (3) and [Cu(pyzt)2(H2O)2]H2O (4), one 1D Cu(II) nitrate quinoxaline structure [Cu(Qux)(NO3)2] (5), two 2D Cu(II) azido quinolinecarboxylate structures [Cu(quCOO)(N3)-(H2O)]n (6) and [Cu(quCOO)(N3)(H2O)]n0.87MeOH (7) and one 2D Cu(II) azido 2,5-dimethylpyrazine structure [Cu(mepyz)(N3)4]n (8). Complexes 1-4, (paper I) were obtained as a result of 2+3-cycloaddition of the azido group to the CN group of pyrazinecarbonitrile ligand. Hydrogen bonds connect the monomeric units of complexes (2), (3) and (4) forming rtl and fsh network topologies, respectively. The thermal stabilities for these complexes were measured by TGA which showed that although tetrazolate complexes are potentially explosives, the Cu(II) complexes (1), (2) and (4) are stable up to 130°C while the Co(II) complex (3) shows higher stability and starts to decompose only around 225°C. In complex (5), (paper II), no azido groups are found in the crystal structure, the 1D chains are formed via bridging µ-N,N’-quinoxaline ligand and the two terminal nitrate groups are forming square planar coordination geometry around the Cu(II) ions. Complexes (6) and (7), (paper II), have both bridging µ1,1–N3 groups and bridging µN,O-quinolinecarboxylate co-ligand forming 2D square grid sheets which are further form six-connected pcu 3D net via hydrogen bonds between sheets. Complex (8), (paper III), has the same azido bridging mode as (6) and (7) µ1,1–N3 and µN,N’-2,5-dimethylpyrazine co-ligand which forms (6,3) 2D net structure. The magnetic susceptibility measurements for (8) shows dominant ferromagnetic interactions between Cu(II) ions through both the azido and the co-ligand bridges.