The interplay between two important non-covalent interactions involving aromatic rings is studied by means of ab initio calculations (MP2/6-31++ G**). They demonstrate that synergetic effects are present in complexes where cation-pi and hydrogen bonding interactions coexist. These synergetic effects have been studied using the 'atoms-in-molecules' theory and the Molecular Interaction Potential with polarization partition scheme. (c) 2008 Elsevier B.V. All rights reserved.