Ds-Block metal ions catalyzed decarboxylation of pyrazine-2,3,5,6-tetracarboxylic acid and the complexes obtained from hydrothermal reactions and novel water clusters

Abstract

The factors that influence the decarboxylation of pyrazine-2,3,5,6-tetracarboxylic acid (H4pztc) under hydrothermal conditions were investigated. Higher temperature and lower pH are very effective promoters for the decarboxylation of H4pztc in the presence of ds-block metal ions. Four novel complexes of H4pztc and four complexes from the decarboxylation of H4pztc, [Zn2(pz25dc)(phen)4](NO3)2·10H2O (1), [Zn2(pztc)(phen)4]·12H2O (2), {[Zn2(pztc)(bpy)2(H2O)2]·2H2O}n (3), [Cu2(pz25dc)(phen)4](NO3)2·10H2O (4), {[Cu2(pztc)(bpy)2 H2O]·4H2O}n (5), [Cu2(H2pztc)(bpy)2(H2O)2](NO3)2·2H2O (6), [Cd(pz26dc)(phen)(H2O)2] (7) and [Cd(pz26dc)(bpy)(H2O)2] (8) (pz25dc = pyrazine-2,5-dicarboxylate, pz26dc = pyrazine-2,6-dicarboxylate, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridyl) have been synthesized and characterized by X-ray single crystal diffraction, elemental analysis, IR, thermal gravimetric analysis (TGA) and fluorescence measurement. 1, 2, 4 and 6 are dinuclear complexes bridged by pztc or pz25dc, 3 and 5 are 1D coordination polymers. In 6, the Cu(II) ions are bridged by bis-tridentate H2pztc2−. 7 and 8 are mononuclear Cd(II) complexes. The 2D or 3D supramolecular structures of 1–8 were built up by hydrogen bonds and π⋯π interactions. Notably, a novel T5(0)A0 water tape and a S-shaped (H2O)10cluster are observed in 2 and 5, respectively.