Torsion effusion vapor pressure determinations of Os, Rh, Ru, W, Co, and Cr solid carbonyls Original Research Article

Vaporization thermodynamics of low and high (>400 g/mol) molecular weight (MW) carbonyls is compared in this study. A gravimetric-torsion effusion method was used to measure vapor pressures of carbonyls such Os3(CO)12, Rh6(CO)16, Ru3(CO)12, Co2(CO)8, Cr(CO)6, and W(CO)6 carbonyls. The vapor pressure thermodynamic data is used for many low and high temperature CVD applications. Disproportionation of solid carbonyls was found to be virtually independent of molecular weight of the species. Vaporization studies of Rh6(CO)16 showed complete decomposition to nano-structured porous metallic Rh metal; the measured MWRh6(CO)16(effusinggas) is 27.75 g/mol was close to that of carbon monoxide as compared to MWRh6(CO)16(solid) of 1065.56 g/mol for the value of solid Rh6(CO)16. However, Ru3(CO)12 and Co2(CO)8 show very complex behavior. The molecular weights of the vaporizing species have been estimated and the numbers of vaporizing species are proposed. For example, there was partial decomposition of Ru3(CO)12 to (approx. 52%) metallic Ru and CO gas during vaporization as suggested by the difference in the molecular weight of the vaporizing species of 107.58 g/mol compared to the actual value of 639.33 g/mol. The dimer Co2(CO)8 partially disproportionates to tetramer Co4(CO)12, monomer Co(CO)4, and CO gas. Whereas, the Os3(CO)12, Cr(CO)6, and W(CO)6 have shown virtually no disproportionation. The total vapor pressures of all the above-mentioned carbonyls, partial pressures of various species, average molecular weights of the effusing gases, equilibrium constants for the vaporization reactions, their enthalpies, entropies, and Gibbs energies have been determined.