Theoretical study of N-H⋯H-B blue-shifted dihydrogen bond

Theoretical calculations were performed to study the nature of the N-H⋯H-B blue-shifted dihydrogen bond in the complex BH3NH3⋯HNO. The geometric structures and vibrational frequencies of the complex BH3NH3⋯HNO at the MP2/6-31+G(d,p), MP2/6-311++G(d,p), B3LYP/6-31+G(d,p) and B3LYP/6-311++G(d,p) levels are calculated by standard and counterpoise-corrected methods, respectively. In the N-H⋯H-B dihydrogen bond, the calculated blue shift of N-H stretching frequency is in the vicinity of 130 cm−1. From the natural bond orbital analysis it can be seen that the N-H bond length in the N-H⋯H-B dihydrogen bond is controlled by a balance of four main factors in the opposite directions: hyperconjugation, electron density redistribution, rehybridization and structural reorganization. Among them hyperconjugation has the effect of elongating the X-H bond, and the other three factors belong to the bond shortening effects. In the N-H⋯H-B dihydrogen bond, the shortening effects dominate which lead to the blue shift of the N-H stretching frequencies. In addition, solvent effect on the geometric structures, vibrational frequencies and interaction energies of the monomer and complex was studied in detail. It is relevant to the relatively dielectric constants (ε).