Synthesis, structure and thermal stability of ternary metal complexes based on polycarboxylate and N-heterocyclic ligands

The reactions of metal salts with pyrazine-2,3-dicarboxylic acid (H2pzdc), pyridine-2,5-dicarboxylic acid (H2pydc), pyrazine-2,3,5,6-tetracarboxylic acid (H4pztc), 4,4′-bipyridine (bipy) and 1,10-phenanthroline (phen) afforded four new ternary complexes, namely [Co2(pzdc)2(bipy)(H2O)2]n·3nH2O (1), [Zn2(pzdc)2(bipy)(H2O)2]n·3nH2O (2), [Co(pydc)2(H2O)2](H2bipy) (3) and [Cu2(pztc)(phen)2(H2O)2]·2HNO3·2H2O (4). The metal centers are all six-coordinated. Compounds 1 and 2 are 2D coordination polymers exhibiting wave-like polymeric networks. The 2D layers are stacked in an interpenetrating mode to form double-layered frameworks, which possess ∼8 Å×6 Å tunnels occupied by (H2O)6 clusters. Compound 3 is a mononuclear supramolecular compound in which 4,4′-bipyridine is protonated and acted as a cationic building block. Compound 4 is a centro-symmetric binuclear complex. Pztc4− as a hexadentate ligand coordinates to two Cu(II) ions to form four chelating rings. Phen are arranged in an ABAB parallel fashion to form a supramolecular architecture incorporating HNO3 lattice molecule. The thermal stabilities of 1−4 and luminescence of zinc complex 2 were also investigated.