Solubility of two metal-organic ruthenium precursors in supercritical CO2 and their application in supercritical fluid technology

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 (scCO(2)) 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 scCO(2), therefore the need of accurate solubility data. The use of scCO(2) as the 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 scCO(2), being the solubility of Ru(tmhd)(2)(COD) at the same pressure and temperature almost five times larger than that of 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 scCO(2). At the conditions of this study, Ru(tmhd)(2)(COD) mole fraction solubility values vary from 2 x 10(-4) to 9 x 10(-4) whilst those for Ru(acac)(3) vary from 2 x 10(-5) to 13 x 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 in the pressure range studied in both ruthenium precursors. Solubility data were satisfactorily correlated to semi-empirical equations which allow the interpolation of solubility data at different conditions. (c) 2012 Elsevier Ltd. All rights reserved.