Flux Synthesis, Structure, Properties, and Theoretical Magnetic Study of Uranium(IV)-Containing A2USi6O15 (A = K, Rb) with an Intriguing Green-to-Purple, Crystal-to-Crystal Structural Transition in the K Analogue

Gregory Morrison; Harry Ramanantoanina; Werner Urland; Mark D Smith; Hans-Conrad zur Loye

doi:10.1021/acs.inorgchem.5b00556

Flux Synthesis, Structure, Properties, and Theoretical Magnetic Study of Uranium(IV)-Containing A2USi6O15 (A = K, Rb) with an Intriguing Green-to-Purple, Crystal-to-Crystal Structural Transition in the K Analogue

Inorg Chem. 2015 Jun 1;54(11):5504-11. doi: 10.1021/acs.inorgchem.5b00556. Epub 2015 May 15.

Authors

Gregory Morrison¹, Harry Ramanantoanina², Werner Urland², Mark D Smith¹, Hans-Conrad zur Loye¹

Affiliations

¹ †Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States.
² ‡Department of Chemistry, University of Fribourg, Chemin du Musée 9, 1700 Fribourg, Switzerland.

PMID: 25978501
DOI: 10.1021/acs.inorgchem.5b00556

Abstract

The flux growth of uranium(IV) oxides presents several challenges, and to the best of our knowledge, only one example has ever been reported. We succeeded in growing two new reduced uranium silicates A2USi6O15 (A = K, Rb) under flux growth conditions in sealed copper tubes. The compounds crystallize in a new structure type with space group C2/c and lattice parameters a = 24.2554(8) Å, b = 7.0916(2) Å, c = 17.0588(6) Å, β = 97.0860(6) ° (K) and a = 24.3902(8) Å, b = 7.1650(2) Å, c = 17.2715(6) Å, β = 96.8600(6) ° (Rb). A2USi6O15 (A = K, Rb) are isocompositional to a previously reported Cs2USi6O15, and the two structures are compared. K2USi6O15 undergoes an interesting crystal-to-crystal structural phase transition at T ≈ 225 K to a triclinic structure, which is accompanied by an intense color change. The magnetic properties of A2USi6O15 (A = K, Rb, Cs) are reported and differ from the magnetism observed in other U(4+) compounds. Calculations are performed on the (UO6)(-8) clusters of K2USi6O15 to study the cause of these unique magnetic properties.