Tensimetric study of β-diketonates of neptunium(VI) and -(IV)

Using the flow method the authors have determined the temperature dependence of the saturated vapor pressure of a series of β-diketonates of neptunium(VI) and -(IV). In studying the complexes Np(PTFA)4 (PTFA = pivaloyltrifluoroacetonate), Np(HFA)4 (HFA = hexafluoroacetylacetonate) and Np(HFA)4 x TMPO (TMPO = trimethylphosphinoxide), the authors observed that the chelate Np(HFA)4, being the most volatile of the listed compounds, at the same time displays insufficient stability; determination of the vapor pressure for this compound was carried out with saturation of the carrier gas with vapors of free H-HFA. It has been established that among the β-diketonates of neptunium(IV), only the adduct NpO2(HFA)2 x TMPO does not undergo reductive decomposition under sublimation conditions at atmospheric pressure. This complex has the same vapor pressure as its uranyl analog. The temperature dependence of the saturated vapor pressure (IIa) for the studied compounds is given in the form of the equation log p = (-A/T) + B. The coefficients A and B, the limits of the temperature interval for the determinations (0C), and also the thermodynamic characteristics of the vaporization process ΔH (kJ/mole) and ΔS(J/(mole.K)) are given