A novel 1:2 proton transfer self-associated compound LH2, (GH+)2(pydc2—), was synthesized from the reaction of dipicolinic acid, pydcH2, (2, 6-pyridinedicarboxylic acid), and guanidine hydrochloride, (GH+)(Cl—). The characterization was performed using IR, 1H and 13C NMR spectroscopy and single-crystal X-ray diffraction. LH2 · H2O crystallizes in the space group C2/c of the monoclinic system and contains eight molecules per unit cell. The unit cell dimensions are: a = 26.480(5)Å, b = 8.055(2)Å, c = 14.068(3)Å. The first coordination complex (GH)2[Cd(pydc)2] · 2H2O, was prepared using LH2 and cadmium(II) iodide, and characterized by 1H and 13C NMR spectroscopy and X-ray crystallography. The crystal system is triclinic with space group P1¯ with one molecule per unit cell. The unit cell dimensions are: a = 8.5125(7)Å, b = 11.0731(8)Å, c = 13.2404(10)Å. The cadmium(II) atom is six-coordinated with a distorted octahedral geometry. The two pydc2— units are almost perpendicular to each other. The protonation constants of the building blocks of the pydc-guanidine adduct, the equilibrium constants for the reaction of pydc2— with guanidine and the stoichiometry and stability of the Cd2+ complex with LH2 in aqueous solution were accomplished by potentiometric pH titration. The solution studies strongly support a self-association between pydc2— and GH+ with a stoichiometry for the CdII complex similar to that observed for the isolated crystalline complex. In fact, the [Cd(pydc)2]2— complex was found as the most abundant species in solution (> 90 %) at a pH >5.
A novel proton transfer self-associated compound from dipicolinic acid and guanidine and its Cadmium(II) complex: synthesis, characterization, crystal structure, and solution studies
ARAGONI, MARIA CARLA;LIPPOLIS, VITO
2004-01-01
Abstract
A novel 1:2 proton transfer self-associated compound LH2, (GH+)2(pydc2—), was synthesized from the reaction of dipicolinic acid, pydcH2, (2, 6-pyridinedicarboxylic acid), and guanidine hydrochloride, (GH+)(Cl—). The characterization was performed using IR, 1H and 13C NMR spectroscopy and single-crystal X-ray diffraction. LH2 · H2O crystallizes in the space group C2/c of the monoclinic system and contains eight molecules per unit cell. The unit cell dimensions are: a = 26.480(5)Å, b = 8.055(2)Å, c = 14.068(3)Å. The first coordination complex (GH)2[Cd(pydc)2] · 2H2O, was prepared using LH2 and cadmium(II) iodide, and characterized by 1H and 13C NMR spectroscopy and X-ray crystallography. The crystal system is triclinic with space group P1¯ with one molecule per unit cell. The unit cell dimensions are: a = 8.5125(7)Å, b = 11.0731(8)Å, c = 13.2404(10)Å. The cadmium(II) atom is six-coordinated with a distorted octahedral geometry. The two pydc2— units are almost perpendicular to each other. The protonation constants of the building blocks of the pydc-guanidine adduct, the equilibrium constants for the reaction of pydc2— with guanidine and the stoichiometry and stability of the Cd2+ complex with LH2 in aqueous solution were accomplished by potentiometric pH titration. The solution studies strongly support a self-association between pydc2— and GH+ with a stoichiometry for the CdII complex similar to that observed for the isolated crystalline complex. In fact, the [Cd(pydc)2]2— complex was found as the most abundant species in solution (> 90 %) at a pH >5.
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