Adduct formation of 18-crown-6 ether (18C6) has been investigated on [RU(NH3)(5)(pz)](PF6)(2) (pz = pyrazine), [Ru(NH3)(5)(dmapy)](PF6)(3) (dmapy = 4-(dimethylamino)pyridine), and [(NH3)(5)Ru(pz)Ru(NH3)(5)](PF6)(5) by spectrophotometry, cyclic voltammetry, and H-1-NMR spectroscopy. The results show that ruthenium(II)- and ruthenium(III)-ammine complexes form the adducts with 18C6 interacting at different ammine sites, that is, at the trans-ammine for the ruthenium(II) complex and at the cis-ammines for the ruthenium(III) complex. The binuclear mixed-valence complex forms the adduct stepwise with 18C6 having 1:2, 1:3, and 1:4 stoichiometries. The formation of an asymmetric 1:3 adduct offers the possibility of partial valence trapping of the delocalized valence over the binuclear complex.