dc.description.abstract
The two complexes (pydaH)₂[Ce(pydc)₂(H₂O)₂]₂.2H₂O (1) and (phenH)₂[Bi(pydc)₂(H₂O)]₂.5H₂O (2) were prepared from the proton transfer compounds containing the 2,6-pyridinedicarboxylate ion. 1 was synthesized from the reaction of Ce(NO)₃.6H₂O with the proton transfer compound, (pydaH₂)(pydc), (pyda=2,6-diaminopyridine, pydcH₂=2,6-pyridinedicarboxylic acid). 2 was synthesized from the reaction of proton transfer compound, (phenH)₂(pydc), (phen=1,10-phenanthroline), with Bi(NO₃)₃.5H₂O. The characterization was carried out using IR, ¹H and ¹³C NMR spectroscopy, elemental analysis and single crystal X-ray diffraction. The complex 1 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) Å, b = 10.503(2) Å, c = 10.774(2) Å, α = 83.905(4)°, β = 88.089(4)°, and γ = 82.636(3)°. 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 P1 of the triclinic system and contains two molecules per unit cell. The unit cell dimensions are: a = 8.8860(4) Å, b = 12.0132(6) Å, c = 13.0766(6) Å, α = 100.967(1)°, β = 96.681(1)° and γ = 94.191(1)°. 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, [Bi(pydc)₂(H₂O)]₂²⁻, (phenH)⁺ counter ions and five lattice waters. In both complexes hydrogen bonds, π-π stacking and ion-pairing play important roles in stabilizing the corresponding lattice. The stoichiometry and stability of the Znᴵᴵ, Cdᴵᴵ, Pbᴵᴵ, and Ceᴵᴵᴵ complexes with (pydaH₂)(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 (pydaH₂)(pydc) with Ceᴵᴵᴵ, obtained in this study, and those with Znᴵᴵ, Cdᴵᴵ and Pbᴵᴵ, reported in our previous studies, are in close agreements. The complexation reactions of phen, pydc, and 2phen+pydc with Biᴵᴵᴵ in aqueous solution were investigated by potentiometric pH titrations, and the equilibrium constants for all major complexes formed are described.
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