Trivalent Cation-Controlled Phase Space of New U(IV) Fluorides, Na₃MU₆F₃₀ (M = Al³⁺, Ga³⁺, Ti³⁺, V³⁺, Cr³⁺, Fe³⁺): Mild Hydrothermal Synthesis Including an in Situ Reduction Step, Structures, Optical, and Magnetic Properties

Author(s)

Jeongho Yeon, University of South Carolina - Columbia
Mark D. Smith, University of South Carolina - ColumbiaFollow
Gregory Morrison, University of South Carolina - Columbia
Hans-Conrad zur Loye, University of South CarolinaFollow

Document Type

Paper

Subject Area(s)

chemistry

Abstract

A series of new, complex U(IV) fluorides, namely, Na₃MU₆F₃₀ (M = Al³⁺, Ga³⁺, Ti³⁺, V³⁺, Cr³⁺, and Fe³+), containing trivalent transition- and main-group metal cations were synthesized via an in situ reduction step of U(VI) to U(IV). Single crystals of the series were grown in high yield under mild hydrothermal conditions and were characterized by single-crystal X-ray diffraction. The reported compounds crystallize in the trigonal space group P3̅c1 and exhibit complex crystal structures with a three-dimensional (3-D) framework composed of corner- and edge-shared UF₉ polyhedra. The arrangement of U₂F₁₆ dimers forms two types of hexagonal channels, where MF6 polyhedra and sodium atoms are located. The most interesting structural feature is the presence of the 3-D framework that can accommodate various transition-metal ions in low oxidation states, indicating that the framework acts as an excellent host. Trivalent transition metal ions, even reduced Ti³⁺and V³⁺, were stabilized by both the rigid framework and by our synthetic conditions. Utilizing ionic radii of transition metal ions, a phase boundary was investigated, suggesting that there exists a size limit for the M site in the crystal structure. The valence state of uranium was studied by U ₄f X-ray photoelectron spectroscopy, which confirmed the presence of U⁴⁺. Temperature-dependent magnetic susceptibility measurements yielded effective magnetic moments of 3.50 and 3.35 μB for Na₃MU₆F₃₀ (M = Al³⁺ and Ga³⁺), respectively. For the other compounds, combined effective magnetic moments of 8.93, 9.09, 9.18, and 10.39 μB were obtained for Ti, V, Cr, and Fe members, respectively. In all cases, large negative Weiss constants were observed, which are indicative of the existence of a spin gap in U⁴⁺. Field-dependent magnetic property measurements at 2 K for Na₃FeU₆F₃₀ demonstrated that U⁴⁺ attains a nonmagnetic singlet ground state at low temperature. Optical and thermal properties were measured and are reported.

Digital Object Identifier (DOI)

https://doi.org/10.1021/ic503034t

Publication Info

Published in Inorganic Chemistry, Volume 54, Issue 4, 2015, pages 2058-2066.

Rights

© Inorganic Chemistry 2015, American Chemical Society.

APA Citation

Yeon, J., Smith, M., Morrison, G., & zur Loye, H.-C. (2015). Trivalent Cation-Controlled Phase Space of New U(IV) Fluorides, Na₃MU₆F₃₀ (M = Al³⁺, Ga³⁺, Ti³⁺, V³⁺, Cr³⁺, Fe³⁺): Mild Hydrothermal Synthesis Including an in Situ Reduction Step, Structures, Optical, and Magnetic Properties. Inorganic Chemistry, 54(4), 2058–2066. https://doi.org/10.1021/ic503034t