A Novel Proton Transfer Compound Containing 2, 6‐Pyridinedicarboxylic Acid and Creatinine and its Zinc(II) Complex — Synthesis, Characterization, Crystal Structure, and Solution Studies

Abstract

AbstractThe 1:1 proton transfer compound LH2, (creatH)+ (pydcH)−, has been prepared from the reaction of creatinine, creat, and dipicolinic acid, pydcH2, (2, 6‐ pyridinedicarboxylic acid) and characterized using IR, 1H and 13C NMR spectroscopy. The first coordination complex (creatH)[Zn(pydc)(pydcH)]·4H2O, was prepared using LH2 and zinc(II) nitrate, and characterized using IR, 1H and 13C NMR spectroscopy and single crystal X‐ray crystallography. The crystal system is triclinic with space group ${\rm P}_{\bar 1}$ with two molecules per unit cell. The unit cell dimensions are a = 8.085(2) Å, b = 10.802(4) Å, c = 13.632(4) Å, α = 104.98(2)°, β = 90.31(2)° and γ = 92.55(3)°. The structure has been refined to a final value for the crystallographic R factor of 0.0381 based on 3003 reflections. The zinc atom is six‐coordinated with a distorted octahedral geometry. The (pydc)2− and (pydcH)− units are almost perpendicular to each other. Extensive hydrogen bondings between carboxylate groups, (creatH)+ and water molecules throughout the zinc(II) complex as well as π–π stacking and ion pairing play important roles in stabilizing the corresponding lattices. The protonation constants of the building blocks of the pydcH2‐creat adduct, the equilibrium constants for the reaction of (pydc)2− with creat and the stoichiometry and stability of the ZnII complex with LH2 in aqueous solution were accomplished by potentiometric pH titration. The solution studies support a self‐associated (creatH)+(pydcH)− as the most abundant species at pH = 3.4. The stoichiometry of the crystalline complex (i.e. (creatH) [Zn(pydc)(pydcH)])and that of the most abundant species detected in solution were found the same.