A Proton Transfer and a Nickel(II) Compound Including Pyridine-2,6-dicarboxylate and Phenylhydrazinium Ions: Synthesis, Characterization, Crystal Structure and Solution Study

The new compounds, (phhyH)(2)(pydc), 1 and (phhyH)[Ni(pydc)(pydcH)]center dot 3H(2)O, 2, phhy: phenylhydrazine, pydcH(2): pyridine-2,6-dicarboxylic acid, were synthesized and characterized by IR, H-1 NMR C-13 NMR and UV spectroscopy. The structure of 2 was determined by X-ray crystallography. In the crystal structure, the metal ion was six coordinated by two tridentate (pydc)(2-) and (pydcH)(-) groups and each anionic complex unit, [Ni(pydc)(pydcH)](-) was accompanied by one (phhyH)(+) as counter ion and two water molecules. In compound 2, a large number 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 hydrogen bonds were observed. These interactions as well as other noncovalent interactions such as ion pairing, C-O center dot center dot center dot pi and pi-pi stacking play an important role in the formation and stabilization of the crystal lattice. In the solution study, the equilibrium constants for the binary pydc-phhy proton transfer system, the stoichiometry and stability of complexation of this system with Ni2+ ion in aqueous solution were investigated using potentiometric pH titration method. The stoichiometry of the most abundant species in the solution was compared to the crystalline cited metal ion complexes.