O-H•••O versus O-H•••S Hydrogen Bonding I: Experimental and Computational Studies on the p-Cresol•H2O and p-Cresol•H2S Complexes

The weak hydrogen bonding ability of sulfur-containing hydrides makes it difficult to study their complexes and has not been characterized experimentally so far. In this work, the hydrogen-bonded complexes of H2S and H2O with p-cresol (p-CR) were studied using a variety of techniques such as two-color resonant two-photon ionization (2c-R2PI) spectroscopy, single vibronic level fluorescence (SVLF) spectroscopy. resonance ion dip infrared spectroscopy (RIDIRS), and fluorescence clip infrared spectroscopy (FDIRS), with an aim of comparing the nature and strength of their respective hydrogen bonding abilities. The intermolecular stretch (sigma) and the shift ill the O-H stretching frequency of p-CR in the complex were taken as the measures of the O-H center dot center dot center dot O and O-H center dot center dot center dot S hydrogen bonding strength. The experiments were complemented by the ab initio calculations, atoms in molecules (AIM), natural bond orbital (NBO), and energy decomposition analyses carried out at different levels of theory. The experimental data indicates that in the p-CR center dot H2S complex. the phenolic OH group acts as a hydrogen bond donor, and sulfur as the acceptor. Further, it indicates that the p-CR center dot H2S complex was about half as strong as the p-CR center dot H2O complex. Tile AIM and NBO analyses corroborate the experimental findings. The energy decomposition analyses for the O-H center dot center dot center dot S hydrogen bond in the p-CR center dot H2S complex reveal that the dispersion interaction energy has the largest contribution to the total interaction energy, which is significantly higher than that in the case of the p-CR center dot H2O complex.