SPONTANEOUS AQUATION REACTIONS OF A PROMISING TUMOR INHIBITOR IDAZOLIUM-TETRACHLOROBIS(IMIDAZOLE)RUTHENIUM(III), TRANS-HIM[RUCL4(IM)(2)]

The spontaneous aquation reaction of trans-RuCl4(Im)(2)(-), Im = imida zole, was studied as a function of pH, chloride concentration, imidazo le buffer and temperature, using spectrophotometric and chromatographi c techniques. The selected pH and chloride concentration control the d egree of aquation observed. In all cases evidence for the formation of RuCl3(Im)(2)H2O was found, which can undergo deprotonation and/or sub sequent aquation depending on the pH and free chloride concentration i n solution. No evidence for aquation of the imidazole ligand was found . The formation of RuCl3(Im)(2)H2O is characterized by a rate constant of 1.5x10(-5) s(-1) at 25 degrees C, Delta H#=117+/-7 kJ mol(-1) and Delta S#=+55+/-23 J K-1 mol(-1). The results are discussed in referenc e to the tumor inhibiting properties of the complex.