Electrospray ionization mass spectrometry (ESIMS) was used to investigate the coordination modes of the complexes [RuII([9]aneS3)(HCpz3)Cl]Cl, [RuII([9]aneS3)(HCpz3)](Cl)PF6 and [RuII([9]aneS3)(HCpz3)](PF6)2 ([9]aneS3 = 1,4,7-trithiacyclononane; HCpz3 = tris(1-pyrazolyl)methane) in methanol, acetonitrile and methanol/water solutions. The complex [RuII([9]aneS3)(HCpz3)Cl]Cl shows a rapidly exchangeable Cl ligand, with formation of a doubly charged ion [RuII([9]aneS3)(HCpz3)]2+, m/z 248, but the [RuII([9]aneS3)(HCpz3)Cl]+, m/z 531, is also observed and both species still coexist after 16 h. The formation of the [RuII([9]aneS3)(HCpz3)]2+ and [RuII([9]aneS3)(HCpz3)Cl]+ ions by electrospraying solutions of [RuII([9]aneS3)(dmso)Cl2] (dmso = dimethylsulfoxide) and HCpz3 in water/methanol was also studied.Fragmentation of the [RuII([9]aneS3)(HCpz3)]2+ ions by losses from the [9]aneS3 ligand seems to point to a k3 strained coordination mode, whereas fragmentation of the [RuII([9]aneS3)(HCpz3)Cl]+ points to a less strained complex and to two isomers: the complex [RuII([9]aneS3)(HCpz3)Cl]+ and the ion pair [RuII([9]aneS3)(HCpz3) + Cl]+. Further support for the ion pair hypothesis is the strong increase of the relative abundance of the [RuII([9]aneS3)(HCpz3) + PF6]+ ion, m/z 641, formed from solutions of the [RuII(k3-[9]aneS3)(k3-HCpz3)](Cl)PF6 and [RuII(k3-[9]aneS3)(k3-HCpz3)](PF6)2 complexes, after 16 h.The high stability of the ion pairs indicates that they may be inner sphere ion pairs and that either [9]aneS3 or HCpz3 changes from a k3 to a k2 coordination mode. The results support an equilibrium between a full k3-[9]aneS3/k3-HCpz3 complex and a k2 + k3 + Cl/PF6 ion pair.