Dispersion-Dominated S–H···Se H-Bonds in the Dimethyl Selenide–H₂S Complex Identified in a Nitrogen Matrix: Cooperative Strengthening by Molecular Nitrogen

The S-H···Se H-bonded complex formation between dimethyl selenide (Me₂Se) and H₂S was studied using Fourier transform infrared (FTIR) spectroscopy in a cold and solid nitrogen (N₂) matrix. Concentration variation and annealing experiments confirmed the formation of the binary Me₂Se-H₂S complex along with larger (1:2 and 2:1) clusters. The S-H···Se H-bonded binary complex exhibited a large red shift of 146.3 cm^-1 in the <i>ν</i>_S-H mode of H₂S. However, the magnitude of the spectral shifts decreased in the larger complexes (113.8-134.2 cm^-1). The binary Me₂Se-H₂S complex was further stabilized, and the <i>ν</i>_S-H transition was even more red-shifted (153.4 cm^-1) due to cooperative strengthening of the existing S-H···Se H-bonds by N₂ molecules forming weak S-H···N H-bonds along with S···N or Se···N van der Waals interactions. The binary Me₂Se-H₂S complex bound by S···Se van der Waals interactions was found to be ∼0.6 kcal mol^-1 less stable than its S-H···Se H-bonded counterpart and could not be identified in the matrix spectra. The binding energy of the S-H···Se H-bonded Me₂Se-H₂S complex was found to be 3.7 kcal mol^-1. The N₂-bound ternary complex exhibited an increased binding energy of 5.2 kcal mol^-1. Furthermore, the binding energies of the two Me₂Se-(H₂S)₂ (1:2) and (Me₂Se)₂-H₂S (2:1) complexes were 6.7, 7.1, and 8.3 kcal mol^-1, respectively. The S-H···Se H-bonds in the Me₂Se-H₂S complex were found to be more than twice as strong, considerably shorter, and more dispersion-stabilized than the S-H···S H-bond in H₂S dimer.