Engineering the Formation of Chalcogen Bonds with Water: I. Heterodimers of the Chalcogen Hydrides H ₂ O–H ₂ X (X = S, Se, Te)

We assess the competing preference for hydrogen and chalcogen bonding in the aqueous heterodimers of the chalcogen hydrides H₂O-H₂X (X = S, Se, Te). We employ the CCSD(T) method near the complete basis set limit and include an explicit account of anharmonic zero-point energy corrections to establish accurate binding energies. We identify three bonding motifs in the H₂O-H₂X dimers, namely, H₂X (i) donating a hydrogen bond, (ii) accepting a hydrogen bond, and (iii) donating a chalcogen bond, and observe the emergence of chalcogen bonds to water for H₂Se and H₂Te. The hydrogen bond donated by a water molecule is consistently more stable than the hydrogen bond donated by the H₂X (X = S, Se, Te) molecule, with the strength of the former decreasing by a smaller margin than the latter down the chalcogen series. Conversely, the chalcogen bond becomes stronger progressing from H₂Se, in which it is weaker, to H₂Te, in which it is more stable than the two other bonding motifs. As a result, the global minimum for H₂O-H₂Te is chalcogen bonded. The analysis of the bonding using quasi-atomic orbitals (QUAOs) offers insights into the nature of the chalcogen- and hydrogen-bond accepting bonding motifs. Specifically, the water molecule prefers to accept hydrogen bonds from its mixed s/p hybrid lone pair and chalcogen bonds from its primarily p-hybridized lone pair. In contrast, the heavier chalcogen hydrides prefer to accept hydrogen bonds from their primarily p-hybridized lone pairs. A remarkable linear correlation exists between the QUAO-derived atomic charges localized on the donor and acceptor heavy atoms and the respective binding energies of the heterodimers.