Vapor Pressures and Enthalpies of Sublimation and Evaporation of Trifluoroacetylacetonates in Helium and Helium Containing the Ligand Vapor

Abstract

The vapor pressures of 21 metal trifluoroacetylacetonates were determined in helium and in helium containing the ligand vapor by using transpiration techniques. The vapor pressure of hydrated chelates can be measured only in helium containing the ligand vapor because considerable thermal decomposition occurs in helium. The volatility is mainly dependent on their structure. The predominant factor that decides volatility of coordination-saturated trifluoroacetylacetonates such as octahedral and tetrahedral chelates is van der Waals forces, while other strong forces are apparent in square-planar and square-pyramidal chelates. From the Clausius-Clapeyron equation, sublimation enthalpies and evaporation enthalpies of coordination-saturated chelates are generally 28 ± 2 and 19 ± 2 kcal mol-1, respectively, and those of cobalt(II), nickel(II), and rare-earth-metal trifluoroacetylacetonates are larger than these values. The values measured by the Freeman-Carroll method for some chelates agreed well with those of the Clausius-Clapeyron equation. © 1985, American Chemical Society. All rights reserved.