Ab initio calculations at the MP2(full)/6-31++G**, RI-MP2(full)/6-31++G**, and RI-MP2(full)/6-311++G(2d,2p) levels of theory demonstrate important synergic effects between two noncovalent interactions that involve aromatic rings, that is, cation-π and π-π interactions. The presence of a cation interacting with the cloud of an aromatic ring favors the face-to-face stacking interaction with additional aromatic rings. This effect is extended in the space up to five stacked aromatic rings.
![MP2 study of cation-(pi)n-pi interactions (n = 1-4)](https://www.iciq.org/wp-content/uploads/2014/03/MP2-study-of-cation-pin_eng_noticies_articles_2006_38.gif)