The importance of ion pairing in different fields of chemistry is widely recognized. In this work, we have synthesized a set of cationic p-cymene ruthenium complexes of general formula [(p-cym)Ru(L')(kappa(2)-(ON)-N-boolean AND-L)]X (p-cym = p-cymene; L' = N-methylimidazole (MeIm), N-ethylpiperidylimidazole (EpipIm), 1,3,5-triaza-7-phosphaadamantane (PTA); L = 2-(1H-benzimidazol-2-yl)phenolato (L1), 2-(1,3-benzothiazol-2-yl)phenolato (L2); X = Cl-, BF4 (-), OTf-, BPh4-). X-ray diffraction studies on selected complexes revealed relatively strong anion-cation interactions in the solid state mainly based on N-H center dot center dot center dot X (X = Cl, F, O) and C-H center dot center dot center dot pi interactions, also observed in the DFT-modeled complexes in the gas phase. Moreover, NMR studies showed that they exist as intimate ion pairs in solution and, remarkably, as head-to-tail quadruples in the particular case of the cation [(p-cym)Ru(MeIm)(kappa(2)-(ON)-N-boolean AND-L1)](+) ([1](+)) with Cl- and BPh4- as counteranions. Furthermore, a value of Delta G = -2.9 kcal mol(-1) at 299 K has been estimated for the equilibrium {[1]BPh4 center dot center dot center dot[1]BPh4}reversible arrow 2{[1](+)center dot center dot center dot BPh4-} in concentrated CDCl3 solutions. In addition, preliminary studies concerning the cytotoxic properties against HeLa cell lines of the derivatives suggested a positive effect derived from the presence of the lipophilic BPh4- anion and also from the NH group of the benzimidazolyl fragment.