The Thermochemical Behavior of Pentaamminedinitrogenruthenium(II) Complexes and the Kinetics of the Liberation of Ammonia from the Complex in the Solid State

Abstract

Abstract The thermochemical reactions of [Ru(NH3)5N2]X2 (X=Cl, Br, I) were investigated in the solid state. The ammonia ligand was liberated at a lower temperature (165–213 °C) than the nitrogen ligand (243–270 °C). The isothermal measurement reveals that the first step of the degradation of the complex can be expressed as: [Ru(NH3)5N2]X2(s)→[RuX(NH3)4N2]X(s)+NH3(g) (X=Cl, Br, or I). The rate of the reaction is first-order to [Ru(NH3)5N2]X2, and the first-order rate constant increased in the order of: chloride<bromide<lodide. The activation energies and the activation entropies (E/kJ mol−1 and ΔS\eweq/J K−1 mol−1 respectively) for the reaction were as follows: chloride (181±1,62±1), bromide (99±1, −95±2), and iodide (89±1, −102±3). The values of ΔS\eweq suggest that the salt with Cl− degrades through an SNl-like mechanism, while those with Br− and I− degrade through an SN2-type mechanism. The thermochemistry of [Ru(NH3)5N2]X2 has been discussed on the basis of the strong π-backbonding ability of the nitrogen ligand and the electronegativity of the outer-sphere ions.