Synthesis and Characterization of Triammine-triaquaruthenium(III) Trifluoromethanesulfonate

Abstract

[ Ru (NH₃)₃(OH₂)₃](CF₃SO₃)₃ was prepared from RuCl₃(NH₃)₃ by using trifluoromethanesulfonic acid and Ag₂CO₃, and characterized by microanalytical , electrochemical and spectroscopic techniques. The complex is soluble in water and in many organic solvents and is a convenient starting material for the preparation of triammine complexes. [RU(NH₃)₃(OH₂)₃]³⁺ has pK_a1 3.77±0.04 and pK_a2 6.93±0.04 at 25°C, and an E_½ of -120 mV at pH 1.5 and -190 mV at pH 5. In the u.v . spectrum λ_max is at 251 nm (є 1150 mol^-1 dm³ cm^-1) in 0.1 M H+ and at 296 nm (є 1760 mol^-1 dm³ cm^-1) at pH 5. [ Ru (NH₃)₄(OH₂)₂]³⁺ has pK_a1 3.96±0.4 and pK_a2 7.09±0.04 and E_1/2 of -140mV at pH 1 and -200mV at pH 5. In the u.v. spectrum λ_max is at 254 nm (є 1200 mol^-1 dm³ cm^-1) in 0.1 M H+ and at 296 nm (є 2650 mol^-1 dm³ cm^-1) at pH 5. [ Ru (NH₃)₃(OH₂)₃]²⁺ can be prepared in situ by reduction with Zn(Hg) or H₂/Pt black; at high pH, the reduction proceeds via a blue mixed-oxidation-state intermediate.