The simplest sulfur-nitrogen hydrogen bond: Matrix isolation spectroscopy of H2S·NH3

Abstract

Hydrogen bonding in SH⋯N systems has received little attention compared to other hydrogen bond motifs. To characterise SH⋯N bonding, infrared spectra of the most fundamental SH⋯N system—the H2S·NH3 complex—were recorded in solid argon. These experiments were complemented by high level ab initio and density functional theory calculations. The H2S symmetric stretch was observed to shift by −155.3 cm−1 when mixed with NH3, while the NH3 umbrella mode was found to shift by +31.8 cm−1. These, as well as deuterium and 15N isotopologue studies indicated the formation of a complex. The structure of the H2S·NH3 complex was determined to be almost identical to that of the H2O·NH3 complex, with a nearly linear SH⋯N bond. A binding energy of 8.6 kJ mol−1 (720 cm−1) was calculated at the CCSD(T) level of theory extrapolated to the complete basis set limit. Anharmonic frequency calculations at the DSD-PBEP86-D3BJ/aug-cc-pV(D+d)Z level of theory produced frequencies with a RMSD of 13 cm−1 for the complex, relative to the experimental values. Comparison with previous work showed that the SH⋯N bond is weaker in H2S·NH3 than the OH⋯N bond in the H2O·NH3 system.