The nature of the intermolecular interaction in (H₂X)₂(X = O, S, Se)

Hydrogen bonds (HBs) are crucial non-covalent interactions in chemistry. Recently, the occurrence of an HB in (H₂S)₂has been reported (Arunanet al.,Angew. Chem., Int. Ed., 2018,57, 15199), challenging the textbook view of H₂S dimers as mere van der Waals clusters. We herein try to shed light on the nature of the intermolecular interactions in the H₂O, H₂S, and H₂Se dimersviacorrelated electronic structure calculations, Symmetry Adapted Perturbation Theory (SAPT) and Quantum Chemical Topology (QCT). Although (H₂S)₂and (H₂Se)₂meet some of the criteria for the occurrence of an HB, potential energy curves as well as SAPT and QCT analyses indicate that the nature of the interaction in (H₂O)₂is substantially different (e.g.more anisotropic) from that in (H₂S)₂and (H₂Se)₂. QCT reveals that the HB in (H₂O)₂includes substantial covalent, dispersion and electrostatic contributions, while the last-mentioned component plays only a minor role in (H₂S)₂and (H₂Se)₂. The major contributions to the interactions of the dimers of H₂S and H₂Se are covalency and dispersion as revealed by the exchange-correlation components of QCT energy partitions. The picture yielded by SAPT is somewhat different but compatible with that offered by QCT. Overall, our results indicate that neither (H₂S)₂nor (H₂Se)₂are hydrogen-bonded systems, showing how the nature of intermolecular contacts involving hydrogen atoms evolves in a group down the periodic table.