Although the coordination chemistry of rhenium complexes is a rapidly expanding research field, little is known about their thermal properties. In this study, we synthesized several rhenium tricarbonyl complexes with tridentate ligands (L) having S or N as donor atoms, fac-[Re(CO)(3) L]X (X = Tf2N [= bis(trifluoromethanesulfonyl)amide)], PF6 ) and fac-[Re(CO)(3)LC1], and investigated their thermal properties and crystal structures. The Tf2N salts were room temperature ionic liquids. The S-coordinated complexes, having longer coordination bonds, were less thermally stable than the N-coordinated complexes. Even though fac[Re(CO)(3)LC1] are bidentate coordination complexes, they were thermally more stable than the isomeric tridentate complexes fac[Re(CO)(3)L] Cl.