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

The spontaneous aquation reaction of trans-RuCl4(Im)(2)(-), Im = imidazole, was studied as a function of pH, chloride concentration, imidazole buffer and temperature, using spectrophotometric and chromatographic techniques. The selected pH and chloride concentration control the degree of aquation observed. In all cases evidence for the formation of RuCl3(Im)(2)H2O was found, which can undergo deprotonation and/or subsequent aquation depending on the pH and free chloride concentration in 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 reference to the tumor inhibiting properties of the complex.