Engineering the Formation of Chalcogen Bonds with Water: I. Heterodimers of the Chalcogen Hydrides H2O–H2X (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.