An ab initio study on boundaries for characterizing cooperative effect of hydrogen bonds by intermolecular compression

The cooperative effect plays a significant role in understanding the intermolecular donor-acceptor interactions of hydrogen bonds (H-bonds, D-H center dot center dot center dot A). Here, using the coupled-cluster singles and doubles with perturbative triple excitations (CCSD(T)) method of high-precision ab initio calculations, we show that the intermolecular H-bonded systems with different D and A atoms reproduce the structural changes predicted by the well-known cooperative effect upon intermolecular compression. That is, with decreasing intermolecular distance, the D-H bond length first increases and then decreases, while the H center dot center dot center dot A distance decreases. On the contrary, when D and A are the same, as the intermolecular distance decreases, the D-H bond length decreases without increasing. This obvious difference means that the cooperative effect may not be generally characterized by intermolecular compression. Interestingly, further analyses of many intermolecular systems confirm that this failure has boundaries, i.e. , cooperative systems at their respective equilibrium positions have a smaller core-valence bifurcation (CVB) index ( < 0.022) and stronger binding energies ( > 0.25 eV), showing a clear linear inverse relationship related to H-bond strength. These findings provide an important reference for the comprehensive understanding of H-bonds and its calculation methods.(c) 2023 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.

Automated summary

The cooperative effect is important in understanding the interactions of hydrogen bonds. Through high-precision ab initio calculations, it is shown that intermolecular H-bonded systems with different donor and acceptor atoms exhibit structural changes predicted by the cooperative effect upon compression. However, when the donor and acceptor are the same, the structural changes are different. Further analysis reveals that the failure of the cooperative effect has boundaries and is related to the H-bond strength.