The synthesis, molecular structure and chemical behavior of two chloride-dimethyl sulfoxide-ruthenium(III) derivatives, namely [(DMSO)2H] [irarts-Ru(DMSO)2Cl4] (1) and mer-Ru(DMSO)3Cl3 (2), are reported. They represent the first examples of fully characterized halogen-dimethyl sulfoxide-ruthenium(III) complexes. Further relevance in their synthesis comes from the known antitumor properties of isostructural Ru(IIl) complexes with heterocyclic nitrogen ligands and of halogen-dimethyl sulfoxideruthcnium(ll) complexes as well. The crystal structures of 1 and 2 have been determined by three-dimensional X-ray analyses.Crystal data are as follows: [(DMSO)2H] [r/-ans-Ru(DMSO)2Cl4], monoclinic, space group Pl/n, a = 9.273 (1) Á, b = 16.509 (3) Á, c = 14.023 (3) Á, ß = 100.79 (2)°, Z = 4, R = 0.041; for mer-Ru(DMSO)3Cl3, monoclinic, space group /'2,/c, a = 10.105 (2) Á, b = 13.832 (3) Á, c = 11.115 (2) Á, ß = 94.39 (2)°, Z = 4, R = 0.028. In 1 there are two crystallographically independent [Ru(DMSO)2C14]" anions lying on crystallographic 2-fold axes, passing through Ru and two trans Cl atoms, so that the other two Cl atoms and the two S-bonded DMSO molecules are also trans to each other. Cations are provided by protonated DMSO molecules, [Me2SO-H-OSMe2]+. In 2 the three chlorine atoms are in the mer configuration, and the two trans DMSO molecules arc S-bondcd to Ru, while the third one is O-bonded. Both complexes are intermediates in the synthesis of cis-RuCl2(DMSO)4 front hydrated RuC13. Cyclic voltammetric evidence shows that, in dimethyl sulfoxide and dichloromethane solution, 2 is in equilibrium with an isomer that very likely differs in the coordination mode of one DMSO (S-to O-bonded isomerization). The chemical behavior of 1 and 2 in aqueous solution has been studied at low pH (<3), where the formation of polymeric species is prevented. When dissolved in water, both complexes rapidly release one of the two trans S-bonded DMSO's and, in about 24 h at room temperature, produce the same neutral species: mer,m-[RuCl3(H20)2(DMS0)]. A completely similar behavior is
