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

Abstract The 1:1 proton transfer compound LH 2 , (creatH) + (pydcH) − , has been prepared from the reaction of creatinine, creat, and dipicolinic acid, pydcH 2 , (2, 6‐ pyridinedicarboxylic acid) and characterized using IR, 1 H and 13 C NMR spectroscopy. The first coordination complex (creatH)[Zn(pydc)(pydcH)]·4H 2 O, was prepared using LH 2 and zinc(II) nitrate, and characterized using IR, 1 H and 13 C 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 pydcH 2 ‐creat adduct, the equilibrium constants for the reaction of (pydc) 2− with creat and the stoichiometry and stability of the Zn II complex with LH 2 in aqueous solution were accomplished by potentiometric p H titration. The solution studies support a self‐associated (creatH) + (pydcH) − as the most abundant species at p H = 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.