The reactions of (ImH)(2)[RuCl(5)Im] (Im = imidazole) in water were monitored by H-1 NMR spectroscopy. Fast initial aquation of [RuCl(5)Im](2-) to [RuCl4(H2O)Im](-) is followed by successive substitutions along two pathways : slow displacement of extra Cl- ligands by water to form higher aquation products and attack of an Im ligand to give [RuCl(4)Im(2)](-), which then aquates. In the presence of 2 equiv of added Im, (ImH)[RuCl(4)Im(2)] gives mixtures of complexes containing three to four Im per Ru, whereas 20 equiv lead to species with five to six Im per Ru. Imidazole-rich species coexist in solution with the starting [RuCl(4)Im(2)](-) ion. X-ray diffraction work on [Ru(OH)(2)Im(4)][RuCl(4)Im(2)] (monoclinic, P2(1)/c, a = 13.126 Angstrom, b = 10.8833 Angstrom, c = 10.6110 Angstrom, beta = 108.280, R = 0.045) shows the presence of octahedral trans-[Ru(OH)(2)Im(4)](+) and trans-[RuCl(4)Im(2)](-) connected by hydrogen bonding. Many complexes and aquation products successively appear when Im is reacted with (ImH)(2)[RuCl(5)Im], and species with five to six Im ligands per Ru are again obtained with 20 equiv of added Im. An end product is isolated as yellow crystals and shown by X-ray diffraction (hexagonal, P6(3)/m, a = 8.9756 Angstrom, c = 20.880 Angstrom, R = 0.023) to be the [RuIm(6)]CO3 . 5H(2)O compound, containing the reduced Ru(II) octahedral [RuIm(6)](2+). In the presence of N6,N6-dimethyladenine (DMAD), [RuCl(4)Im(2)](-) in water slowly forms the [RuCl(3)Im(2)(DMAD)] complex, in which the adenine ligand is monodentate.