Structural and reactivity changes in ruthenium ammines induced by the NO ligand

Abstract

The crystal structure of [Ru(NH 3) 5(OH 2)] 2(S 2O 6) 3 · 2H 2O has been solved by X-ray diffraction techniques. The relevant average interatomic distances are Ru–(NH 3) eq=2.09 Å, Ru–(NH 3) ax=2.08 Å and Ru–(OH 2) ax=2.11 Å. The aquation rate ( k H 2O ) and the activation parameters for the reaction trans -[ RuNO( NH 3) 4 Cl] 2++ H 2 O → k H 2 O trans -[ RuNO( NH 3) 4( H 2 O)] 3++ Cl − have been calculated as 8.4 × 10 −6 s −1 (0.10 mol L −1 CF 3COOH, μ=0.10 mol L −1, 40 °C), Δ H ≠ −1=2.3 kcal mol −1, Δ S ≠ −1=24.0 cal deg −1 mol and Δ G ≠ −1=8.6 kcal mol −1. A comparison between the structural data, kinetic and thermodynamic reactivities of [Ru(NH 3) 5(OH 2)] 3+ and trans-[RuNO(NH 3) 4(OH 2)] 3+ ions strongly suggests that the substitution of the trans NH 3 ligand in the coordination sphere of [Ru(NH 3) 5(OH 2)] 2+ by NO confers a character of Ru(III) to the formally Ru(II) center.