Coulombic energy in bromide salts of mononitrogen organic bases

Abstract

The electrostatic part of the lattice energy in bromide salts of mononitrogen organic bases has been determined adopting the Ewald method. The calculations were carried out for the compounds for which the complete or at least the partial crystal structure is known. In the case of incomplete structures the MNDO geometry optimisation procedure was applied to find the unknown positions of atoms. The electrostatic energy calculations were performed on the assumption that a negative (– 1) charge is attached to the bromine atom and a positive (+1) charge is either located on the nitrogen atom or distributed among all the atoms in the cation. The charge distribution in the isolated cation was evaluated applying CNDO/2, INDO and MNDO methods. The electrostatic energy values derived were compared with the published values of the crystal lattice energy determined either theoretically or experimentally. The agreement appeared to be satisfactory, which implies that, in bromide salts of mononitrogen bases, the magnitude of the cohesive forces is predominantly accounted for by coulombic interactions.