An experimental and theoretical study of a hydrogen-bonded complex: O-phenylenediamine with 2,6-pyridinedicarboxylic acid

摘要

The hydrogen-bonded complex, [(OPDH)(+)(dipicH)(-)center dot H2O], between o-phenylenediamine (OPD) and 2,6pyridinedicarboxylic acid (dipicH2) has been characterized in water by the H-1, C-13 NMR and IR spectroscopies. The crystal structure showed that the edge to face C-H center dot center dot center dot pi and C-O center dot center dot center dot pi stacking interactions between the dipicH2 and OPD rings play an extra significant role in the formation of the hydrogenbonded complex and supported the H-bonding interactions. The proton transfer also investigated theoretically in gas phase and thermodynamic parameters such as Delta H, Delta G, Delta S1 were calculated for this process. Moreover, intramolecular hydrogen-bonding interaction has been recognized by calculating the electron density rho(r) and Laplacian del(2)p(r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM) method and also the interaction between electron acceptor (sigma*) of OH with the lone pair of the nitrogen atom as an electron donor using Natural Bond Orbital (NBO) analysis. In addition, the protonation constants of dipicH(2) and OPD and the equilibrium constants for the dipic-OPD (1:1) proton transfer system were obtained by the potentiometric pH titration method using the Hyperquad 2008 program. The stoichiometry of the proton transfer species in the solution confirmed the solid state result. (C) 2015 Elsevier B.V. All rights reserved.