Solution and solid-state studies of a new supramolecular proton transfer salt and its VO2 complex constructed with chelidamic acid and 3,4-diaminopyridine

Abstract

The proton transfer compound (Hdap)(chelH)·2H2O (1) and its related anionic complex (Hdap) [VO2(chel)] (2), where chelH2 = 4-hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid) and dap = 3,4-diaminopyridine, were synthesized and characterized by elemental analysis, spectroscopy (IR, UV–Vis), thermal (TG/DTG) analysis and single-crystal X-ray diffraction. Compound 1 resulted from proton transfer between chelH2 and dap in aqueous solution. In 1, two carboxylic acids of chelH2 were deprotonated and the protons transferred to the nitrogen atoms of one chelidamate anion and one dap moiety. Compound 2 resulted from complexation of 1 and vanadyl sulfate. In the crystal structure of 2, the metal ion is five coordinated by one tridentate ligand (chel)2− and two O2− anions, with (Hdap)+ as a counter cation. In both structures, a complicated hydrogen-bonding network accompanied with π–π, C–O···π and C–H···π stacking interactions leads to formation of a 3D supramolecular network. In the following, solution studies have been performed by means of pH potentiometric titrations method as a power technique. This method was used for determination of protonation constants of chelH2 and dap in their probable protonated forms and for calculation of equilibrium constants for the chelH2–dap proton transfer system and the stoichiometry and stability constants of binary and ternary complexes of this system with VO2+ ion in aqueous solution. The stoichiometries of the most complex species in solution were compared with the corresponding crystalline complexes in the solid state.