Crystal structures and solution studies of two novel Zinc(II) complexes of a proton transfer compound obtained from 2,6-pyridinedicarboxylic acid and 1,10-phenanthroline: Observation of strong intermolecular hydrogen bonds

The proton transfer compound LH(2), (phenH(+))(2)(pydc(2-)), has been prepared from 1,10-phenanthroline, phen, and 2,6-pyridinedicarboxylic acid, (dipicolinic acid), pydcH(2). Characterization was performed using solution and solid phase CP/MAS (13)C NMR and IR spectroscopy The reactions of this adduct with ZnSO(4).-7H(2)O and Zn(NO(3))(2).4H(2)O give the complexes, [Zn(pydc)(2)][Zn(phen)(2)(H(2)O)(2)].7H(2)O (1) and [Zn(phen)(3)]4(H(Hpydc)(2))(NO(3))(7).26H(2)O (2), respectively. These complexes were characterized by (1)H and (13)C NMR spectroscopy and single crystal X-ray analysis. The complexes crystallize in the triclinic space group P (1) over bar with Z = 2. The unit cell dimensions for complex 1 and 2 are: a = 9.9838(9) Angstrom, b = 14.7483(13) Angstrom, c = 14.8365(13) Angstrom and a = 12.640(4) Angstrom, b 15.855(5) Angstrom, c = 21.830(7) Angstrom, respectively. In complex 1 (pydc(2-)) and phen, are tri- and bidentate ligands, respectively, and an anionic [Zn(pydc(2)](2-) and cationic [Zn(phen)(2)(H(2)O)(2)](2+) complex are formed simultaneously. In cornplex 2, three phen participate in complexation leaving hydrogenbis(pyridine-2-carboxylate), (H(HpydC)(2))(-) as a supramolecular anion. The fragments (H(HpydC)(2))(-), 7 NO(3)(-), and 26 H(2)O in complex 2 are joined together by extensive and strong H-bonding; therefore, the structure is composed of [Zn(phen)(3)](4)(8+), and an anionic hydrogen bond supramolecular assembly with the formula, {(H(Hpydc)(2)(NO(3))(7))(8-).26H(2)O}(n). The anionic species (H(Hpydc)(2))(-) has a special position at the inversion center, as well as one of the NO(3)(-) anions, which is disordered over the inversion center. Most of the hydrogen bonds in complex 2 represent strong H-bonding. The protonation constants of the building blocks of the pydc-phen adduct, the equilibrium constants for the reaction of (pydc(2-)) With phenanthroline and the stoichiometry and stability of the Zn(11) complex with LH(2) on aqueous solution were determined by potentiometric pH titration. The solution study results support self-association between (pydc(2-)) and (phenH(+)) with a stoichiornetry for the Zn(II) complex similar to that observed for the isolated crystalline complex.