Ionic liquids comprised of cationic arene-ruthenium chelate complexes and the bis-(trifluoromethanesulfonyl)amide anion (=Tf2N), [(arene)-RuCl(L)](Tf2N), where L = MeS(CH2)(n)SR (R = Me, Bu; n = 1-3), Me2N(CH2)(2)NMe2 and arene = p-cymene, C6H6, have been prepared, and their thermal properties, structures, and reactivities have been investigated. These liquids undergo direct ligand exchange reactions in line with their thermal stabilities. Thermogravimetric analysis revealed that the thermal stabilities of the complexes are higher as the bridging group of the chelate ligand becomes longer. The complexes with MeSCH2SMe transform thermally into dinuclear complexes. The coordination structures were determined crystallographically.