Yeon Jeongho, Smith Mark D, Morrison Gregory, zur Loye Hans-Conrad
Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States.
Inorg Chem. 2015 Feb 16;54(4):2058-66. doi: 10.1021/ic503034t. Epub 2015 Feb 5.
A series of new, complex U(IV) fluorides, namely, Na3MU6F30 (M = Al(3+), Ga(3+), Ti(3+), V(3+), Cr(3+), and Fe(3+)), 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 Ti(3+) and V(3+), 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 U(4+). Temperature-dependent magnetic susceptibility measurements yielded effective magnetic moments of 3.50 and 3.35 μB for Na3MU6F30 (M = Al(3+) and Ga(3+)), 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 U(4+). Field-dependent magnetic property measurements at 2 K for Na3FeU6F30 demonstrated that U(4+) attains a nonmagnetic singlet ground state at low temperature. Optical and thermal properties were measured and are reported.
通过将U(VI)原位还原为U(IV)，合成了一系列新的、复杂的U(IV)氟化物，即Na3MU6F30（M = Al(3+)、Ga(3+)、Ti(3+)、V(3+)、Cr(3+)和Fe(3+)），其中包含三价过渡金属和主族金属阳离子。该系列单晶在温和水热条件下高产率生长，并通过单晶X射线衍射进行表征。报道的化合物结晶于三方空间群P3̅c1，具有由角共享和边共享的UF9多面体组成的三维（3-D）骨架的复杂晶体结构。U2F16二聚体的排列形成了两种类型的六边形通道，MF6多面体和钠原子位于其中。最有趣的结构特征是存在能够容纳各种低氧化态过渡金属离子的三维骨架，这表明该骨架是一种优异的主体。三价过渡金属离子，甚至是还原态的Ti(3+)和V(3+)，都通过刚性骨架和我们的合成条件得以稳定。利用过渡金属离子的离子半径，研究了相界，表明晶体结构中M位点存在尺寸限制。通过U 4f X射线光电子能谱研究了铀的价态，证实了U(4+)的存在。温度依赖的磁化率测量得出，Na3MU6F30（M = Al(3+)和Ga(3+)）的有效磁矩分别为3.50和3.35 μB。对于其他化合物，Ti、V、Cr和Fe成员的组合有效磁矩分别为8.93、9.09、9.18和10.39 μB。在所有情况下，都观察到了较大的负魏斯常数，这表明U(4+)中存在自旋能隙。在2 K下对Na3FeU6F30进行的场依赖磁性测量表明，U(4+)在低温下达到非磁性单重态基态。测量并报道了光学和热学性质。
