Synthesis, thermogravimetric analysis and enthalpy determination of lanthanide β-diketonates

This work reports thermodynamic characterizations of lanthanide β-diketonates for use in nuclear fission product separation. Adsorption and sublimation enthalpies have been shown to be linearly correlated, therefore there is motivation to determine sublimation thermodynamics. An isothermal thermogravimetric analysis method is employed on fourteen lanthanide chelates for the ligands 2,2,6,6-tetramethyl-3,5-heptanedione and 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione to determine sublimation enthalpies. No linear trend is seen across the series; values show a cyclical nature, possibly indicating a greater influence of chemisorption for some complexes and less of a role of physisorption in dictating adsorption differences between lanthanides in the same series. This is in line with previous reports in terms of the chromatographic separation order of the lanthanides. The results reported here can be used to manipulate separations parameters and column characteristics to better separate these lanthanide chelates. Fourteen chelates of the ligand 1,1,1-trifluoro-2,4-pentanedione are also thermally characterized but found to not sublime and be undesirable for this method. Additionally, all chelates are characterized by constant heating thermogravimetric analysis coupled with mass spectrometry, melting point analysis, elemental analysis and FTIR.