A Revised Structure Model for the UCl 6 Structure Type, Novel Modifications of UCl 6 and UBr 5 , and a Comment on the Modifications of Protactinium Pentabromides

Research output: Contribution to journalArticleScientificpeer-review


  • H. Lars Deubner
  • Stefan S. Rudel
  • Malte Sachs
  • Clemens Pietzonka
  • Antti J. Karttunen
  • Sergei I. Ivlev
  • Matthias Müller
  • Matthias Conrad
  • Ulrich Müller
  • Florian Kraus

Research units

  • University of Marburg


The redetermination of the crystal structure of trigonal UCl 6 , which is the eponym for the UCl 6 structure type, showed that certain atomic coordinates had been incorrectly reported. This led to noticeably different U−Cl distances within the octahedral UCl 6 molecule (2.41 and 2.51 Å). Within the revised structure model presented here, which is based on single crystal data as well as quantum chemical calculations, all U−Cl distances are essentially equal within standard uncertainty (2.431(5), 2.437(5), and 2.439(6) Å). This room temperature modification, called rt-UCl 6 , crystallizes in the trigonal space group P (Formula presented.) m1, No. 164, hP21, with a=10.907(2), c=5.9883(12) Å, V=616.9(2) Å 3 , Z=3 at T=253 K. A new low-temperature (lt) modification of UCl 6 is also presented that was obtained by cooling a single crystal of rt-UCl 6. The phase change occurs between 150 and 175 K. lt-UCl 6 crystallizes isotypic to a low-temperature modification of SF 6 in the monoclinic crystal system, space group C2/m, No. 12, mS42, with a=17.847(4), b=10.8347(18), c=6.2670(17) Å, β=96.68(2)°, V=1203.6(5) Å 3 , Z=6 at 100 K. The Cl anions form a close-packed structure corresponding to the α-Sm type with uranium atoms in the octahedral voids. During the synthesis of UBr 5 a new modification was obtained that crystallizes in the triclinic crystal system, space group P (Formula presented.), No. 2, aP36, with a=10.4021(6), b=11.1620(6), c=12.2942(7) Å, α=68.3340(10)°, β=69.6410(10)° and γ=89.5290(10)°, V=1231.84(12) Å 3 , Z=3 at T=100 K. In this structure the UBr 5 units are dimerized to U 2 Br 10 molecules. The Br anions also form a close-packed structure of the α-Sm type with adjacent uranium atoms in the octahedral voids. Comparisons of the crystal structures of the compounds MX 5 (M=Pa, U; X=Cl, Br) show that the crystal structure of monoclinic α-PaBr 5 is probably not correct.


Original languageEnglish
Pages (from-to)6402-6411
Number of pages10
JournalChemistry - A European Journal
Issue number25
Publication statusPublished - 2 May 2019
MoE publication typeA1 Journal article-refereed

    Research areas

  • bromide, chloride, crystal structures, protactinium, uranium

ID: 33285847