Sublimation enthalpy of tetrakis(1, 1, 1, 5, 5, 5-hexafluoro-2, 4-pentanedionato)lanthanide(III)-potassium complexes, KLn(C5HF6O2)4: Effect of lanthanide contraction. (April 2019)

• Record Type: Journal Article
• Authors: Khochenkov, Aleksey E.; Belova, Natalya V.; Krasnov, Alexander V.; Zhabanov, Yuriy A.; Giricheva, Nina I.; Girichev, Georgiy V.
• Is Part Of: Journal of chemical thermodynamics. Volume 131(2019)
• Page Start: 117
• Page End: 121
• Publication Date: 2019-04
• Subjects: Tetrakis(1, 1, 1, 5, 5, 5-hexafluoro-2, 4-pentanedionato)lanthanide(III)-potassium -- β-Diketonates -- Lanthanides -- Mass spectrometry -- Enthalpy of sublimation; Thermodynamics -- Periodicals; Thermochemistry -- Periodicals; Thermodynamique -- Périodiques; Thermochimie -- Périodiques; Thermochemistry; Thermodynamics; Periodicals; 541.369
• DOI: 10.1016/j.jct.2018.10.033
• Languages: English
• ISSNs: 0021-9614

Abstract

Graphical abstract: Highlights: Congruent sublimation of KLn(C5 HF6 O2 )4 complexes was observed. Sublimation enthalpy of complexes was obtained by Knudsen effusion method. Molecular structure of KLn(C5 HF6 O2 )4 complexes calculated by DFT. Coordination number of K + equals six in gaseous complex and twelve in crystal. Enthalpy decrease correlates with lanthanide contraction and weakening the KO ionic bonds. Abstract: The mass spectra of tetrakis(1, 1, 1, 5, 5, 5-hexafluoro-2, 4-pentanedionato)lanthanide(III)-potassium complexes KLn(C5 HF6 O2 )4, where Ln = La, Gd, Lu, (hereinafter referred to as KLn(hfa)4 ), have been recorded at different temperatures. The presence of the high-intensity ions KLn(hfa)3 + generated by elimination of one ligand from the parent species due to electron ionization indicates that the saturated vapours of all three complexes consist of the only KLn(hfa)4 species. The sublimation enthalpies were determined by effusion Knudsen method in frame of second law of thermodynamics. The vaporization was studied over temperature ranges 414 ÷ 471 К for KLa(hfa)4, 401 ÷ 453 К for KGd(hfa)4, and 399 ÷ 442 К for KLu(hfa)4 . The values of Δsub H°(T) equal 170.6 ± 2.1, 166.4 ± 3.6, and 161.8 ± 2.3 kJ/mol for the complexes of La, Gd and Lu respectively. DFT/PBE0 calculations show, that the shortening of the MO bond length due to lanthanide contraction is accompanied by a decrease in the negative net charge on the oxygen atoms bounded with potassium. The potassium ions play the role of the bridges between the [Ln(hfa)4 ] − anions in the crystal, and weakening the KO ionic bonds can explain the decrease in the enthalpy of sublimation of the lutetium complex in comparison with the lanthanum one.