Mixed-ligand zinc(II) complex, {(pipzH 2 )[Zn(hypydc)(btc) 0.5 ]·H 2 O} 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···O, N–H···O and C–H···O with D···A ranging from 2.630(2) to 3.347(3) Å, ion pairing and C–O···π stacking interactions connect the various components into a supramolecular structure. The quaternary complex system including of hypydcH 2 –btcH 4 –pipz and Zn 2+ ion, has been investigated. The stoichiometry and stability constants of binary complexes including each of ligands (hypydcH 2 , btcH 4 , pipz) in presence of Zn 2+ 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 Zn 2+ ion were calculated in aqueous solutions by potentiometric pH titration method.
Graphical Abstract
A novel polymeric mixed-ligand zinc(II) complex, {(pipzH 2 )[Zn(hypydc)(btc) 0.5 ]·H 2 O} n containing 4-hydroxypyridine-2,6-dicarboxylic acid, benzene-1,2,4,5-tetracarboxylic acid and piperazine was synthesized and characterized.