Synthesis, X-ray crystal structure, thermal and solution studies of a centrosymmetric metal-organic polymer based on proton transfer methodology

A 3-D metal-organic coordination polymer based on pyrazine-2,3-dicarboxylic acid (pzdcH2) formulated as {[Mn(pzdc)(H2O)2] center dot 2H2O}n (1), was obtained by the treatment of MnCl2 center dot 6H2O with pzdcH2, 8-hydroxy quinoline (8-HQ), and 2-amino-4-methyl pyridine (ampy). In this study, we describe the synthesis, elemental analysis, IR spectroscopy, TG analysis, and single X-ray diffraction. The X-ray single crystal structure reveals that the chemical environment around each Mn(II) is a distorted octahedral by participating one nitrogen, five oxygens from three (pzdc)2- and two water molecules, O5MnN. The centrosymmetric 1-D ladder-like structure of 1 is bridged by oxygens of (pzdc)2-, and Mn-pzdc-Mn bonds are the rungs for our ladder structure. In the crystal structure, intermolecular O-H center dot center dot center dot O hydrogen bonds result in the formation of a supramolecular structure, effective for the stabilization of the structure. The thermal decomposition of 1 indicates that it is quite thermally stable. The protonation constants of ampy, 8-HQ and pzdcH2 as the building blocks of proton transfer systems including pzdcH2-ampy and pzdcH2-8-HQ and the corresponding stability constants of these systems were determined by potentiometric study. The stoichiometry and stability constants of complexes of pzdcH2-ampy and pzdcH2-8-HQ with Mn2+ were investigated by this method in aqueous solution. The results obtained from solution study are comparable with the solid state results.