Synthesis, characterization, crystal structure and solution studies of a novel proton transfer (charge transfer) complex of 2,2′-dipyridylamine with 2,6-pyridine dicarboxylic acid

Abstract

Reaction between 2,2′-dipyridylamine (DPA) and 2,6-pyridine dicarboxylic acid (dipicolinic acid, dipicH2), in water results in the formation of a proton transfer or charge transfer (CT) complex, (DPAH)+(dipicH)−·H2O, 1. The characterization was performed using 1H NMR and FTIR spectroscopy, elemental analysis and X-ray crystallography. The crystal system is triclinic with space group P1. The structural investigations exhibit that the hydrogen bonds and π–π stacking interactions stabilize the crystal structure of proton transfer complex. The protonation constants of 2,6-pyridine dicarboxylic acid, 2,2′-dipyridylamine and the equilibrium constants for dipic–DPA (1:1) proton transfer system were calculated by potentiometric pH titration method using Hyperquad2008 program. The stoichiometries of the proton transfer species in solution was in agreement with the solid state result.