Vapor pressures of osmium, rhodium, and ruthenium carbonyls

Vapor pressures of solid Os-3(CO)(12),Rh-6(CO)(16), and Ru-3(CO)(12) were d etermined by the gravimetric torsion effusion method. The vapor pressures o f Os-3(CO)(12) ranged from 10(-6) to 10(-3) kPa at 349 to 396 K. There was virtually no decomposition of the Os-3(CO)(12), and the measured molecular weight was nearly the same as that of the actual value of 906.7 g/mol, The vaporization studies of Rhs(CO)(16) showed that it decomposed to Rh metal b etween 325 and 365 K. The measured molecular weight of the effusing gas fro m the solid Rh-6(CO)(16) was 27.75 g/mol, close to that of carbon monoxide compared to the values expected in absence of decomposition of 1065.56 g/mo l, The Ru-3(CO)(12) vaporization was complex as there was partial decomposi tion (approximately 52%) of the carbonyl to metallic Ru, as suggested by th e 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 total vapor pressures of these three carbonyls, the average molecular weights of the effusing ga ses, equilibrium constants for the vaporization reactions, their enthalpies , entropies, and Gibbs energies have beers determined.