Cooperativity of the Chalcogen Bond Juxtaposed to the Hydrogen Bond in the (H2X)n, X = O, S, Se, Te, n = 3, 4 Clusters

Clusters of chalcogen hydrides (H2X)n (X = O, S, Se, Te) provide a powerful testbed for probing their bonding motifs, namely, the competing preference between hydrogen and chalcogen bonds, and their cooperativity. The analysis of 37 trimer and 50 tetramer minima suggests chalcogen bonding is less cooperative than hydrogen bonding in clusters of the heavier chalcogen hydrides. Chalcogen bonds first appear for the higher-lying unlinked local minima in (H2S)3, are present in both the unlinked and ring minima in (H2Se)3, and finally stabilize an “all-chalcogen-bonded” ring global minimum in (H2Te)3. Hydrogen and chalcogen bonds are both associated with unique infrared spectral signatures, with the band manifold closely following their prevalence in the cluster. Three-body contributions are stronger for planar hydrogen-bonded and weaker for planar chalcogen-bonded structures; the cooperativity of chalcogen bonds is maximized in nonplanar boat configurations, while the cooperativity of hydrogen bonds is minimized in fused trimer configurations. The much smaller 3-body and negligible 4-body terms for the hydrides of the heavier chalcogens signify a qualitative departure from the prevailing picture regarding the importance of nonadditive contributions in water, for which the 3-body is much stronger and the 4-body not negligible. These results have a profound effect on the development of interaction potentials for the hydrides of the heavier chalcogens and provide a stepping stone in the study of their markedly different macroscopic thermodynamic properties with respect to water.