THERMODYNAMICS OF THE EQUILIBRIUM SYSTEM RU3(CO)12-RU(CO)5-CO

The Ru3(CO)12/Ru(CO)5-equilibrium was investigated. It was observed, that the rate of equilibration is slow even at higher temperatures (e.g. ca. 550 h at 100-degrees-C, 25.0 bar CO in isooctane and ca. 10 h at 150-degrees-C, 5.4 bar CO in n-hexane). It is about doubled if the carbon monoxide contains 2% H-2. The ruthenium concentrations were measured by IR spectroscopy using a high pressure infrared cell. Thorough solubility and density measurements were performed for carbon monoxide in n-hexane. The temperature dependence of the equilibrium constant, extrapolated to 1 bar, is given by the equation ln K(a)-degrees = ln K(x)-degrees = -7.32 + 1560/T. For the temperature range 100-degrees-175-degrees-C, the enthalpy of reaction, DELTA-H(R)-degrees, calculated therefrom is -13.0 +/- 1.1 kJ/mol and the entropy of reaction, DELTA-S(R)-degrees, is -60.8 +/- 2.6 J/mol K. From the former, an enthalpy of formation, DELTA-H(f)-degrees {Ru(CO)5} of -714 +/- 10 kJ/mol and an enthalpy of disruption, DELTA-H(disr)-degrees {Ru(CO)5}, of 819 +/- 11 kJ/mol can be calculated. The mean Ru-Ru bond dissotation enthalpy, R(Ru-Ru), is 159 +/- 3 kJ/mol, the one for the Ru-CO bond, D(Ru-CO), is 164 +/- 2 kJ/mol.