MP2 Study of Cation-(pi)n-pi Interactions (n = 1-4).

[eng] 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-ð and ð-ð interactions. The presence of a cation interacting with the ð 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