Noble gas induced surprisingly higher stability of π hydrogen bonded complex: comparative study of hydrogen bonded complexes of HKrCCH and HCCH with H2O, NH3, CH3OH and CH3NH2

Structure, energetics and spectroscopic properties of hydrogen bonded complexes of HKrCCH with H2O, NH3, CH3OH and CH3NH2 have been explored as well as compared with the hydrogen bonded complexes of its precursor HCCH. The most stable structure for HKrCCH is the pi (O/N-H center dot center dot center dot pi) hydrogen bonded complex, whereas the sigma (C-H center dot center dot center dot O/N) hydrogen bonded complex is most stable for HCCH. Surprisingly, the stabilization energy of the pi hydrogen bonded complex of HKrCCH is about two to three fold higher compared to the sigma hydrogen bonded complex of HCCH, which is in contrast to the general perception that the strength of pi hydrogen bond is less compared to sigma hydrogen bond. From the atom in molecule and charge analyses, it has been found that pi hydrogen bonded complexes of HKrCCH have a cyclic structure in which O/N-H center dot center dot center dot pi hydrogen bonding takes place along with Kr center dot center dot center dot O/N interaction. Higher stabilization energy of the pi hydrogen bonded complex of HKrCCH is due to a cooperative phenomena in which Kr center dot center dot center dot O/N interaction contributes to the formation of a strong O/N-H center dot center dot center dot pi hydrogen bonding.