Proton and Lithium Cations Linked to π-Electron and σ-Electron Systems: Are Such Interactions beyond or within the Definition of Hydrogen/Lithium Bond?

MP2/aug-cc-pVTZ calculations were performed on systems containing a proton or a lithium cation located between two pi-electron systems or between pi-electron and sigma-electron units. The proton or the lithium cation attached to the acetylene or its derivative may be treated as the Lewis acid unit while the remaining part of the complex, the pi-electron species or the dihydrogen, act as the Lewis base through their pi-electrons or sigma-electrons, respectively. The complexes analysed here are linked by the pi center dot center dot center dot H+/Li+center dot center dot center dot pi and pi center dot center dot center dot H+/Li+center dot center dot center dot sigma interactions. It is discussed whether these interactions are classified as hydrogen and lithium bonds. Therefore, different definitions of the latter interactions are presented. The Electron Localization Function (ELF) and the Natural Bond Orbital (NBO) approaches were applied to analyse the above-mentioned complexes. The unique properties of interactions with the proton and with the lithium cation that occur in complexes analysed here are described.

Automated summary

MP2/aug-cc-pVTZ calculations were performed on systems containing a proton or a lithium cation located between two pi-electron systems or between pi-electron and sigma-electron units. The nature of interactions between these systems, including whether they can be classified as hydrogen or lithium bonds, was discussed. The properties of the interactions with the proton and with the lithium cation in the analyzed complexes were described using the Electron Localization Function and the Natural Bond Orbital approaches.