A very rare tetravalent uranium germanate has been synthesized under hydrothermal conditions at 585 °C and 160 MPa. Its structure contains layers of single-ring Ge(3)O(9)(6-) germanate anions that are connected by UO(6) octahedra and dimers of edge-sharing GeO(5) trigonal bipyramids to form a three-dimensional framework with intersecting 6- and 7-ring channels. UV-visible, photoluminescence, and U 4f X-ray photoelectron spectroscopy were used to confirm the valence state of uranium.
A new mixed-valence uranium germanate and the silicate analogue have been synthesized under hydrothermal conditions at 600 °C and 165 MPa. Their crystal structures contain infinite -U(V)-O-U(IV/V)-O-U(IV/V)-O-U(V)- chains that are connected by Ge(2)O(7) or Si(2)O(7) groups to form a 3D framework with six-ring channels where the Cs(+) cations are located. Two of the Cs sites in the germanate are partially occupied. Bond-valence-sum calculation and an U 4f X-ray photoelectron spectroscopy study confirm the valence states of the uranium.
A pentavalent uranium germanate, Cs(3)UGe(7)O(18), was synthesized under high-temperature, high-pressure hydrothermal conditions at 585 °C and 160 MPa and structurally characterized by single-crystal X-ray diffraction and infrared spectroscopy. The valence state of uranium was confirmed by X-ray photoelectron spectroscopy and electron paramagnetic resonance. The room-temperature EPR spectrum can be simulated with two components using an axial model that are consistent with two distinct sites of uranium(V). In the structure of the title compound, each ([6])GeO(6) octahedron is bonded to six three-membered single-ring ([4])Ge(3)O(9)(6-) units to form germanate triple layers in the ab plane. Each layer contains nine-ring windows; however, these windows are blocked by adjacent layers. The triple layers are further connected by UO(6) octahedra to form a three-dimensional framework with intersecting six-ring channels along the <1 ̅10> directions. The Cs(+) cation sites are fully occupied, ordered, and located in the cavities of the framework. Pentavalent uranium germanates or silicates are very rare, and only two uranium silicates and one germanate analogue have been published. However, all of them are iso-structural with those of the Nb or Ta analogues. In contrast, the title compound adopts a new structural type and contains both four- and six-coordinate germanium. Crystal data of Cs(3)UGe(7)O(18): trigonal, P3̅c1 (No. 165), a = 12.5582(4) Å, c = 19.7870(6) Å, V = 2702.50(15) Å(3), Z = 6, D(calc) = 5.283 g·cm(-3), μ(Mo Kα) = 26.528 mm(-1), R(1) = 0.0204, wR(2) = 0.0519 for 1958 reflections with I > 2σ(I). GooF = 1.040, ρ(max,min) = 1.018, and -1.823 e·Å(-3).
A mixed-valence uranium(IV,VI) germanate has been synthesized under high-temperature, high-pressure hydrothermal conditions. The structure contains discrete U(IV)O(6) octahedra and U(VI)O(6) tetragonal bipyramids, which are connected by three-membered single-ring Ge(3)O(9)(6-) anions to form a three-dimensional framework with 9-ring channels. The U 4f X-ray photoelectron spectroscopy spectrum was measured to identify the valence states of the uranium.
A very rare organically templated niobium germanate was synthesized and structurally characterized by single-crystal X-ray diffraction. The crystal shows an intense second harmonic generation signal. It is the first example of the synthesis of organically templated metal germanate using an ionic liquid as a solvent.
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