A novel coordination polymer of zinc(II) atom, [(pipzH2)[Zn(pyzdc)2].6H2O]n (1) (H2pyzdc and pipz are pyrazine-2,3- dicarboxylic acid and piperazine, respectively), was successfully synthesized under hydrothermal conditions and structurally characterized by means of elemental analysis, FTIR, TGA and SEM. Polymer 1 was further structurally characterized by single crystal X-ray diffraction consisting of 1D-polymeric units. The crystal structure of the title polymer consisted of polymeric Zn complex anions and discrete piperazindiium cations. The Zn cation, located on the inversion center, was N,O-chelated by two (pyzdc)2- anions in the basal plane, and was further coordinated by two carboxyl O atoms from the adjacent pyzdc anions in the axial directions with a longer Zn-O bond distance of 2.1746(15) Å, forming a distorted ZnN2O4 coordination geometry. The pyzdc anions bridged the Zn cations to the one-dimensional polymeric chains running along the crystalographic b axis. The (pipzH2)2+ linked with the complex chains via kinds of hydrogen bonds. The polymer 1 crystallized in the monoclinic space group P21/n with Z = 2. The cell parameters of the title polymer were a = 6.5318(16) Å, b = 17.492(4) Å, c = 10.688(3) Å and

= 100.841(4)°. The polymer 1 bears ion-pairing interactions, O-H…O, N-H…O, and C-H…O hydrogen bonds as main factors in the formation of its 1D supramolecular architecture. Obtained results from TGA showed that the title polymer was thermally quite stable, and so its framework possessed remarkable thermal stability up to 700 °C. The SEM analysis verified that layers present in 1 were formed in Nano-sized particle. The protonation constants of acridine (Acr), H2pyzdc, and pipz as the building blocks of the proton transfer systems including pyzdc-Acr in mixed 20% dioxane-80% water (V/V) solvent and pyzdc-pipz in aqueous solvent, and the corresponding stability constants of these systems were determined by potentiometric study. The stoichiometry and stability of complexation of these systems with Zn2+ ion were investigated by potentiometric pH titration method. The stoichiometry of the most complex species in the solution was compared with the corresponding crystalline metal ion complexes.

Keywords