How the cation-cation π-π stacking occurs: A theoretical investigation into ionic clusters of imidazolium

The cation-cation pi-pi stacking is uncommon but it is essential for the understanding of some supramolecular structures. We explore theoretically the nature of non-covalent interaction occurring in the stacked structure within modeled clusters of 1,3-dimethylimidazolium and halide. The evidences of the energy decomposition analysis (EDA) and reduced density gradient (RDG) approach are different from those of common pi-pi interaction. Isosurfaces with RDG also illustrate the strength of the titled pi-pi interaction and their region. Additionally, we find that the occurrence of this interaction is attributed to a few C-H center dot center dot center dot X interactions, as depicted using atom in molecule (AIM) method. This work presents a clear picture of the typical cation-cation pi-pi interaction and can serve to advance the understanding of this uncommon interaction. (C) 2015 Elsevier Inc. All rights reserved.