Quantum chemical modeling of the enthalpy of formation for guanidinium bitetrazole salts

The enthalpies of formation for bitetrazole guanidinium salts in the gas and solid phases were calculated using the standard approach and isodesmic reaction method. A comparative analysis of the quality of the methods and the basis sets (HF, 3-21G, 6-31G, 6-311⁺⁺G(d, p); DFT/B3LYP, 3-21G, 6-31G(d)) was performed for the calculation of the molecular volumes necessary for modeling the enthalpies of formation in solid phase, and the optimum set was recommended. The calculated values of enthalpies of formation of the compounds obtained by the isodesmic reaction method are three times lower than the results obtained using standard procedures.