Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The solubility of ruthenium(III) acetylacetonate [Ru(acac)3] and bis(2,2,6,6-tetramethyl-3,5-heptanedionato)( 1,5-cyclooctadiene) ruthenium(II) [Ru(tmhd)2(COD)] in supercritical CO2 (scCO2) was measured using a high-pressure variable volume view cell between the temperatures 313 K and 353 K and pressures up to 20.0 MPa. Both compounds have been proposed as precursors in the synthesis of ruthenium containing materials using scCO2, therefore the need of accurate solubility data. The use of scCO2 as solvent in metallization processes yields materials of exceptional properties and, at the same time, represents a sustainable alternative to conventional techniques thus bringing environmental and economic benefits. These metal-organic compounds exhibit different solubility behaviour in scCO2, being the solubility of Ru(tmhd)2(COD) at the same pressure and temperature almost five times larger than that Ru(acac)3. The dissolution rate is also much faster for Ru(tmhd)2(COD). The shielding of the metal centre by the bulkier ligands in Ru(tmhd)2(COD) favours dissolution of this compound in scCO2. At the conditions of this study, Ru(tmhd)2(COD) mole fraction solubility values vary from 2 10 4 to 9 10 4 whilst those for Ru(acac)3 vary from 2 10 5 to 13 10 5. For a given temperature, the solubility increases with pressure due to the higher density of the solvent. At constant pressure, the solubility decreases with temperature due to the decrease in density of the fluid. The crossover phenomenon was not observed the pressure range studied in both ruthenium precursors. Solubility data were satisfactorily correlated semi-empirical equations which allow the interpolation of solubility data at different conditions.