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.