Comparative Study on Crystal Structures and Synthetic Techniques of Ternary Hafnium/Zirconium Fluorides.

Mild hydrothermal synthesis was employed to grow high-quality single crystals of ternary fluoridohafnates at low temperatures. The series of new materials was characterized using single-crystal X-ray diffraction, and the crystal structures of AHfF6 (A = Mg and Sr), A2HfF8 (A = Ba and Pb), Ca5Hf3F22, and Cd2HfF8(H2O)6 are discussed herein. Although some material compositions have similar stoichiometries, all of the compositions adopt different structural motifs. A comparison of the crystal structures and synthesis techniques of ternary fluoridohafnates and ternary fluoridozirconates is also reported, and the impact of the subtle changes of synthesis conditions on overall structures is discussed.

Luminescence and Scintillation of [Nb2O2F9]3--Dimer-Containing Oxide-Fluorides: Cs10(Nb2O2F9)3F, Cs9.4K0.6(Nb2O2F9)3F, and Cs10(Nb2O2F9)3Cl.

We report three novel Nb-containing oxide-fluorides, Cs10(Nb2O2F9)3F, Cs9.4K0.6(Nb2O2F9)3F, and Cs10(Nb2O2F9)3Cl, which were prepared as high-quality single crystals via a HF-based mild hydrothermal route. The compounds all crystallize in the trigonal crystal system with space group P3̅m1. All three compositions form the same framework structure consisting of isolated [Nb2O2F9]3- dimers that create hexagonal channels that are occupied by disordered halide species. Upon excitation by UV light at room temperature, these compounds display broad band emission with a maximum at 440 nm for Cs10(Nb2O2F9)3F. The broad band emission of these compounds is attributed to the charge-transfer transitions of Nb-O bonds within the [Nb2O2F9]3- dimers. All three compounds scintillate blue under X-ray irradiation. Radioluminescence (RL) measurements performed on Cs10(Nb2O2F9)3F demonstrate that the RL emission intensity decreases with increasing temperature and that the integrated RL emission (300-750 nm) is 4% of Bi4Ge3O12 (BGO) powder. Thermogravimetric analysis confirms that Cs10(Nb2O2F9)3F has excellent thermal stability up to 600 °C and no structural phase transition is observed prior to sample decomposition.

Synthesis of Hydrated Ternary Lanthanide-Containing Chlorides Exhibiting X-ray Scintillation and Luminescence.

A series of new ternary lanthanide-based chlorides, Cs2EuCl5(H2O)10, Cs7LnCl10(H2O)8 (Ln = Gd or Ho), Cs10Tb2Cl17(H2O)14(H3O), Cs2DyCl5(H2O)6, Cs8Er3Cl17(H2O)25, and Cs5Ln2Cl11(H2O)17 (Ln = Y, Lu, or Yb), were prepared as single crystals via a facile solution route. The compounds with compositions of Cs7LnCl10(H2O)8 (Ln = Gd or Ho) and Cs5Ln2Cl11(H2O)17 (Ln = Y, Lu, or Yb) crystallize in a monoclinic crystal system in space groups C2 and P21/c, respectively, whereas Cs2EuCl5(H2O)10, Cs10Tb2Cl17(H2O)14(H3O), and Cs8Er3Cl17(H2O)25 crystallize in orthorhombic space groups Pbcm, Pnma, and P212121, respectively. Cs2DyCl5(H2O)6 crystallizes with triclinic symmetry in space group P1̅. All of these compounds exhibit complex three-dimensional structures built of isolated lanthanide polyhedral units that are linked together by extensive hydrogen bonds. Cs2EuCl5(H2O)10 and Cs10Tb2Cl17(H2O)14(H3O) luminesce upon irradiation with 375 nm ultraviolet light, emitting intense orange-red and green color, respectively, and Cs10Tb2Cl17(H2O)14(H3O) scintillates when exposed to X-rays. Radioluminescence (RL) measurement of Cs10Tb2Cl17(H2O)14(H3O) in powder form shows that the RL emission integrated in the range of 300-750 nm was ∼16% of BGO powder.

BaWO2F4: a mixed anion X-ray scintillator with excellent photoluminescence quantum efficiency.

A new self-activated X-ray scintillator, BaWO2F4, with an excellent photoluminescence quantum efficiency is reported. Hydrothermally grown single crystals, space group P2/n, exhibit a 3D framework structure containing isolated WO2F4 octahedra. BaWO2F4 exhibits green emission under UV light with a high quantum yield of 53% and scintillates when exposed to X-rays(Cu).

Expansion of the Na3 MIII (Ln/An)6 F30 Series: Incorporation of Plutonium into a Highly Robust and Stable Framework.

Nan MAn6 F30 is an extremely versatile framework structure for incorporating tetravalent actinides (An) and cerium along with divalent or trivalent d-metals (M); moreover, the structure exhibits a high resistance to harsh chemical conditions. This extreme robustness can potentially be exploited for the sequestration of plutonium in a stable matrix; however, no Nan MPu6 F30 compounds have been reported so far. Herein, we present four new plutonium fluorides that have been prepared as single crystals by mild hydrothermal synthesis methods. Structural characterizations revealed their compositions to be Na3 AlPu6 F30 , Na3 FePu6 F30 , Na3 CoPu6 F30 , and Na2.4 Mn1.6 Pu6 F30 . Surprisingly, in the plutonium series, it was found that Co2+ and Mn2+ precursors oxidized to form Na3 CoIII Pu6 F30 and Na2.4 MnII/III 1.6 Pu6 F30 , whereas the analogous reactions for cerium result in reduction of the transition metal, even when beginning with a M3+ precursor. While cerium is often used as a surrogate for plutonium, this work serves as an example that deviations between their chemistries do occur.

Quaternary cerium(iv) containing fluorides exhibiting Ce3F16 sheets and Ce6F30 frameworks.

A series of new Ce(iv) based fluorides with two different compositions, Cs2MCe3F16 (M = Ni2+, Co2+, Mn2+, and Zn2+) and Na3MCe6F30 (M = Al3+, Ga3+, Fe3+, and Cr3+) were synthesized as high quality single crystals via a mild hydrothermal route. The compounds with the composition Cs2MCe3F16 (M = Ni2+, Co2+, Mn2+, and Zn2+) crystallize in the hexagonal crystal system with space group P63/mmc and are isotypic with the uranium analogs, whereas the Na3MCe6F30 (M = Al3+, Ga3+, Fe3+, and Cr3+) compounds crystallize in the trigonal space group P3[combining macron]c1 and are isotypic with the uranium and thorium analogs NaxMM'6F30 (M' = Th, U). The Cs2MCe3F16 compounds exhibit a complex 3D crystal structure constructed of edge-sharing cerium trimers, in which all three Ce atoms share a common µ3-F unit. The Na3MCe6F30 compounds are constructed of edge- and vertex-sharing cerium polyhedra connected to each other to form Ce6F306- framework, which can accommodate only relatively smaller trivalent cations (M3+ = Al3+, Ga3+, Fe3+, and Cr3+) as compared to uranium and thorium analogs. Magnetic susceptibility measurements were carried out on the samples of Cs2MCe3F16 (M = Ni2+ and Co2+), which exhibit paramagnetic behavior.

Mild Hydrothermal Synthesis of the Complex Hafnium-Containing Fluorides Cs2[M(H2O)6][Hf2F12] (M = Ni, Co, Zn), CuHfF6(H2O)4, and Cs2Hf3Mn3F20 Based on HfF7 and HfF6 Coordination Polyhedra.

A series of new Hf(IV)-containing fluorides with three different compositions, Cs2[M(H2O)6][Hf2F12] (M = Ni, Co, Zn), CuHfF6(H2O)4, and Cs2Hf3Mn3F20, were synthesized as high-quality single crystals via a mild hydrothermal route. The compounds with compositions of Cs2[M(H2O)6][Hf2F12] (M = Ni, Co, Zn) and CuHfF6(H2O)4 crystallize in the monoclinic space groups P21/n and P21/c, respectively, while the Cs2Hf3Mn3F20 phase crystallizes in the orthorhombic space group Pmmn. Cs2[M(H2O)6][Hf2F12] (M = Ni, Co, Zn) exhibits a complex three-dimensional (3D) crystal structure consisting of edge-sharing dimers of HfF7 polyhedra, which are linked to the divalent metal octahedra via hydrogen bonding. Cs2Hf3Mn3F20 features corner-sharing HfF7 and MnF7 dimers as well as isolated MnF6 octahedra, while the CuHfF6(H2O)4 phase exhibits a 3D structure that consists of HfF6 octahedra linked with neighboring copper octahedral units by hydrogen-bonding interactions. UV-vis spectra of the title compounds were collected and exhibit absorption bands due to electronic transitions in the divalent metal cations (Ni2+, Co2+, Cu2+, and Mn2+). Magnetic susceptibility measurements revealed paramagnetic behavior in the compounds containing the magnetic cations Ni, Co, Cu, and Mn.