Application of a Mild Hydrothermal Approach Containing an in Situ Reduction Step to the Growth of Single Crystals of the Quaternary U(IV)-Containing Fluorides Na₄MU₆F₃₀ (M = Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) Crystal Growth, Structures, and Magnetic Properties

Abstract

A family of rare U(IV)-containing quaternary fluorides, Na4MU6F30 (M = Mn(2+), Co(2+), Ni(2+), Cu(2+), and Zn(2+)), was synthesized in single crystal form via a mild hydrothermal technique utilizing an in situ U(VI) to U(IV) reduction step. The modified hydrothermal route is described, and the conditions to obtain single crystals in high yield are detailed. The crystal structures were determined by single crystal X-ray diffraction. The isostructural fluorides crystallize in a new structure type in the trigonal space group P3̅c1. They exhibit a complex three-dimensional crystal structure consisting of corner- and edge-shared UF9 and MF6 polyhedra. The main building block, a U6F30(6-) group, is arranged to create two distinct hexagonal channels, inside which MF6 octahedra and Na(+) cations are located. The copper-containing member of the series, Na4CuU6F30, is unusual in that the Cu(2+) cation exhibits a rare symmetrical coordination environment consisting of six identical Cu-F bond distances, indicating the lack of the expected Jahn-Teller distortion. Magnetic susceptibility measurements of Na4ZnU6F30 yielded an effective magnetic moment of 3.42 μB for the U(4+) (f(2)) cation in the structure. Measurements of the other members containing magnetic transition-metal cations in addition to U(4+), Na4MU6F30 (M = Mn(2+), Co(2+), Ni(2+), and Cu(2+)) yielded total effective magnetic moments of 10.2, 9.84, 8.87, and 8.52 μB for the Mn-, Co-, Ni-, and Cu-containing materials, respectively. No evidence for long-range magnetic ordering was found down to 2 K. Measurements of the magnetization as a function of applied magnetic field at 2 K for Na4MnU6F30 confirmed that the U(4+) magnetic cation exhibits a nonmagnetic singlet ground state at low temperature. Thermal stability measurements and UV-vis diffuse reflectance spectroscopy are also reported.

Expanding pentafluorouranates: hydrothermal synthesis and characterization of β-NaUF5 and β-NaUF5·H2O

“…10,11 More recently, a number of ternary and quaternary hydrated, hydronium, alkali, and transition metal uranium uorides have been reported for potential applications as phases for separation of actinides or use in molten ux reactors. [12][13][14][15][16][17][18][19][20] These studies yielded the rst high-quality structural data of rhombohedral Na 7 U 6 F 31 , as well as the rst syntheses of NaUF 5 and NaU 2 F 9 . The development of the copper-catalyzed U 6+ /U 4+ in situ reduction step by Yeon, et al 19 has led to the production of over a dozen new ternary and quaternary uranium uorides, but the remarkable stability of Na 4 CuU 6 F 30 inhibited the production of sodium uranium uorides until recently.…”

“…The development of the copper-catalyzed U 6+ /U 4+ in situ reduction step by Yeon, et al 19 has led to the production of over a dozen new ternary and quaternary uranium uorides, but the remarkable stability of Na 4 CuU 6 F 30 inhibited the production of sodium uranium uorides until recently. 17 Copper appears to catalyse the production of U 3 F 12 (H 2 O) from uranyl solution. 19 Resultingly, further work by this research group maintained the use of copper catalyst throughout its work with uranium(IV) uorides.…”

Hydrothermal syntheses and characterization of two novel luminescent Cadmium(II) frameworks: From 1D infinite triple Cd-(trz)-Cd bridges to a rare I2O0 network with 2D Cd–Br–Cd inorganic connectivity

“…All 1,2,4-triazole rings are fairly planar; the deviation from the least-squares plane through the ring atoms is smaller than 0.01(1) Å. The Cd-N bond distances vary from 2.339(2) Å to 2.357(0) Å, which fall in the normal range of Cd-N bond distances [16]. As shown in Fig.…”

Flux crystal growth and structural analysis of two cesium uranium oxides, Cs2.2U5O16and Cs2U4O13, containing multiple cation–cation interactions

“…36 In the current work, the uranium polyhedra also adopt a sheet structure. 38 The magnetic susceptibility, shown in Fig. All of the CCIs present in the structure arise due to the connection of the U(2) polyhedra into the sheet, as shown for Cs 2.2 U 5 O 16 in Fig.…”