Synthesis and crystal structure of Ce-III and Bi-III complexes and solution studies of Zn-II, Cd-II, Pd-II, Ce-III, and Bi-III complexes obtained from proton transfer compounds containing 2,6-pyridinedicarboxylate ion

The two complexes (pydaH)(2)[Ce(pydC)(2)(H2O)(2)](2) (.) 2H(2)O (1) and (phenH)(2)[Bi(pydc)(2)(H2O)](2) (.) 5H(2)O (2) were prepared from the proton transfer compounds containing the 2,6-pyridinedicarboxylate ion. I was synthesized from the reaction of Ce(NO)(3) (.) 6H(2)O with the proton transfer compound, (pydaH(2))(pydc), (pyda = 2,6-diaminopyridine, pydcH(2) = 2,6-pyridinedicarboxylic acid). 2 was synthesized from the reaction of proton transfer compound, (phenH)2(pydc), (phen = 1,10-phenanthroline), with Bi(NO3)(3) (.) 5H(2)O. The characterization was carried out using IR, H-1 and C-13 NMR spectroscopy, elemental analysis and single crystal X-ray diffraction. The complex I crystallizes in the space group P1 of the triclinic system, and contains two molecules per unit cell. The structure has been refined to a final value for the crystallographic R factor of 0.0342 based on 8851 reflections. The unit cell parameters are: a = 9.753(2) angstrom, b = 10.503(2) angstrom, c = 10.774(2) angstrom, alpha = 83.905(4)degrees, beta = 88.089(4)degrees, and gamma = 82.636(3)degrees. The crystal structure illustrates that cerium atoms are connected together through the four-membered ring Ce2O2. 2,6-Pyridinedicarboxylate fragment acts as a tridentate ligand. The molecular structure contains four (pydc)(2-) ligands, two of which are bridge ligands linking the two central atoms. The complex 2 crystallizes in the space group P! of the triclinic system and contains two molecules per unit cell. The unit cell dimensions are: a = 8.8860(4)angstrom, b = 12.0132(6)angstrom, c = 13.0766(6) angstrom, alpha = 100.967(1)degrees, beta = 96.681 (1)degrees and gamma = 94.191 (1)degrees. The structure has been refined to a final value for the crystallographic R factor of 0.0471 based on 9576 reflections. In this complex, 2,6-pyridinedicarboxylate moiety has acted as a tridentate ligand and the lattice is composed of binuclear unit, 2[Bi(pydc)(2)(H2O)](2)(2-), (phenH)(+) counter ions and five lattice waters. In both complexes hydrogen bonds, pi-pi stacking and ion-pairing play important roles in stabilizing the corresponding lattice. The stoichiometry and stability of the Zn-II, Cd-II, Pb-II, and Ce-III complexes with (pydaH(2))(pydc) in aqueous solution were investigated by potentiometric pH titration. The solution studies revealed that the stoichiometry of the crystalline complexes of the proton transfer system (pydaH(2))(pydc) with Ce-III, obtained in this study, and those with Zn-II, Cd-II and Pb-II, reported in our previous studies, are in close agreements. The complexation reactions of phen, pydc, and 2phen+pydc with Bi-III in aqueous solution were investigated by potentiometric pH titrations, and the equilibrium constants for all major complexes formed are described.