The Zinc(II) Coordination Polymer with Mixed-Ligand of 4-Hydroxypyridine-2,6-dicarbolic Acid and Benzene-1,2,4,5-tetracarboxylic Acid in the Presence of Piperazine as a Counter Ion: Synthesis, Crystal Structure and Solution Study

Mixed-ligand zinc(II) complex, {(pipzH(2))[Zn(hypydc)(btc)(0.5)]center dot H2O} (n) , (1) was prepared with 4-hydroxypyridine-2,6-dicarboxylic acid (hypydcH(2)), benzene-1,2,4,5-tetracarboxylic acid (btcH(4)) and piperazine (pipz). This compound is composed of an anionic complex, [Zn(hypydc)(btc)(0.5)](2-), protonated piperazine as a counter-ion, (pipzH(2))(2+) and one uncoordinated water molecule. The three donor atoms of the (hypydc)(2-) and two donor atoms of bridged (btc)(4-) ligands form a distorted square pyramid arrangement around the Zn-II center. In the crystal structure of the title compound, a wide range of non-covalent interactions consisting of hydrogen bonding (of the types of O-H center dot center dot center dot O, N-H center dot center dot center dot O and C-H center dot center dot center dot O with D center dot center dot center dot A ranging from 2.630(2) to 3.347(3) , ion pairing and C-O center dot center dot center dot pi stacking interactions connect the various components into a supramolecular structure. The quaternary complex system including of hypydcH(2)-btcH(4)-pipz and Zn2+ ion, has been investigated. The stoichiometry and stability constants of binary complexes including each of ligands (hypydcH(2), btcH(4), pipz) in presence of Zn2+ ion, ternary complexes including each two of three ligands (hypydcH(2)-btcH(4), hypydcH(2)-pipz, btcH(4)-pipz) in presence of metal ion and finally quaternary systems including three ligands (hypydcH(2)-btcH(4)-pipz) and Zn2+ ion were calculated in aqueous solutions by potentiometric pH titration method. A novel polymeric mixed-ligand zinc(II) complex, {(pipzH(2))[Zn(hypydc)(btc)(0.5)]center dot H2O} (n) containing 4-hydroxypyridine-2,6-dicarboxylic acid, benzene-1,2,4,5-tetracarboxylic acid and piperazine was synthesized and characterized.