Thermochemical study of the dicyanoimidazole isomers

The standard (p° = 0.1 MPa) molar enthalpy of formation at T = 298.15 K for 4,5-dicyanoimidazole, in the crystalline phase, was derived from the standard molar energy of combustion measured by static bomb combustion calorimetry. This value and the literature value of the standard molar enthalpy of sublimation of the compound allow the calculation of the corresponding gas-phase standard molar enthalpy of formation, at T = 298.15 K. Additionally, theoretical calculations for 4,5-dicyanoimidazole were performed by density functional theory with the hybrid functional B3LYP and the 6-31G(d) basis set, extending the study to the 2,4- and 2,5-dicyanoimidazole isomers. Single-point energy calculations for both molecules were determined at the B3LYP/6-311+G(2df,2p) level of theory. With the objective of assessing the quality of the results, standard ab initio molecular orbital calculations at the G3 level were also performed. Enthalpies of formation, obtained using appropriate working reactions, were calculated and compared with the experimental data.