Intermolecular C-H•••H-M dihydrogen bonds in five-membered heterocyclic complexes: a DFT and ab-initio study

In this work, dihydrogen bond between five-membered heterocyclic compounds (furan, thiophene, pyrrole, arsole, borole, phosphole, and silole) and alkali metal hydride HM (M = Li, Na, and K) were carried out by density functional theory and ab-initio calculations. A two pure (PBE, M06L) and four hybrids (B3LYP, B3P86, B3PW91, wB97XD) DFT functional and MP2 method with 6-311 + + G** basis set were used for five membered heterocyclic dihydrogen bond interactions. Molecular geometries, puckering parameters, energies, and natural bond orbital analysis of all the complexes were calculated by various DFT functionals and MP2 method. For all the complexes, smallest H center dot center dot center dot H bond distance is observed for thiophene center dot center dot center dot HK which has significant interaction energy (Delta E-C), while largest H center dot center dot center dot H distance with smallest Delta E-C is observed for pyrrole center dot center dot center dot HLi complex. Among all the functionals, M06L predicted the smallest dihydrogen bond distances for all the complexes, while largest dihydrogen bond distance was observed by B3LYP functional. The infrared vibrational frequency analysis for all the complexes has revealed propensities in red and blue shift for the C-H and M-H bonds, respectively. Natural bond orbital and quantum theory of atom in molecules analyses were performed to examine the nature of interaction along with the molecular electrostatic potential which further confirm the existence of dihydrogen bonding.