The labile cationic aqua complexes, trans(O,S)-[Ru(bpy)Cl(dmso-S) 2(OH2)]X (1•X; X- = PF6 - or OTf-: CF3SO3 -) have been prepared by the treatment of cis(Cl),cis(S)-[Ru(bpy)Cl2(dmso-S) 2] with Ag+ in water at room temperature. When 1•X is dissolved in DMSO, MeOH, or MeCN, the OH2 ligand in 1+ is replaced with a solvent molecule (L) to yield trans(L,S)-[Ru(bpy)Cl(dmso-S) 2(L)]+ (L = dmso-O, 2+; L = MeOH, 3 +; and L = MeCN, 4+), respectively. Moreover, 2•(OTf) is also obtained by the reaction of cis(Cl),cis(S)-[Ru(bpy)Cl 2(dmso-S)2] with Ag(OTf) in DMSO on refluxing. The four kinds of crystal structures of trans(L,S)-[Ru(bpy)Cl(dmso-S)2(L)]PF6 (1•PF6•H2O, 2•PF6, 3•PF6, and 4•PF6•MeCN) revealed that the structural parameters, except for the sixth axial ligand, were essentially the same, and the four ligands, the bpy, two dmso-S, and the equatorial Cl- ligands are connected by hydrogen bonding. All the OH2, dmso- O, MeOH, or MeCN ligands on the sixth coordination site at the axial position in cationic mono(bpy)ruthenium(II) complexes are labile so they are interconvertable. The [Ru(bpy)Cl(dmso-S)2] unit does not change at room temperature even in solutions due to the presence of hydrogen networks among the bpy, two dmso-S, and the equatorial Cl- ligands.