Thorium Cluster Synthesized by a Solvent-Free Flux Approach: The Richest Coordination Diversity and Application Exploration.

The renaissance of research interests in actinide oxo clusters in the past decade arises from both the concerns of radioactive contamination and their potential utility as nanoscale materials. Compared to the uranium cluster, the thorium (Th) cluster shows less coordination variation. Herein, we presented a unique Th cluster (ThC-1) that exhibits the most diverse coordination chemistry found within a single Th cluster via a solvent-free flux synthesis approach. The melt triazole not only offers a unique solvation environment that may be responsible for the coordination diversity in ThC-1 but also represents the first nitrogen-donor capping ligand in Th clusters. The potential utility of ThC-1 as a heterogeneous catalyst was also explored for a classical CO2 cycloaddition reaction. This work offers a novel approach in synthesizing Th clusters, broadening the realm of the structural diversity of Th.

Dithio-Fused Boron Dipyrromethenes: Synthesis and Impact of S-Heteroaromatic Annulation Mode.

Three dithio-fused boron dipyrromethenes (BODIPYs), DTFB-1, DTFB-2, and DTFB-3, in which symmetrically S-heteroaromatic ring units fused at [a], zigzag, and [b] bonds of the parent BODIPY core, respectively, were prepared from the facile and efficient post-functionalization of tetra-halogenated BODIPYs through Pd-catalyzed cyclization. Dithio-fusion at various positions of BODIPY effectively tunes their photophysical properties and single-crystal structural packing arrangements. The single-crystalline microribbons of DTFB-2 exhibit commendable hole mobilities in air, reaching up to 0.03 cm2 V-1 s-1.

Effect of Tb3+ and Ce3+ Co-doping on the Structure and Photoluminescence Properties of Hexagonal Boron Nitride Phosphors.

In the paper, we have successfully prepared hexagonal boron nitride (h-BN:Tb3+, Ce3+) phosphors with melamine as the nitrogen source. The X-ray powder diffraction patterns confirm that the sample possesses a hexagonal crystal structure within the P 6 ¯ m2 space group. It is interesting that the co-doping combination of Tb3+ and Ce3+ can markedly enhance the threshold concentration of doped activators within the limited solid solution of h-BN phosphors. Under 302 nm excitation, the h-BN:Ce3+ phosphors exhibit broadband blue light emission at 406 nm. In h-BN:Tb3+, Ce3+ phosphors, the co-doping of Ce3+ not only ensures high phase purity but also results in strong green light emission. The energy transfer efficiency from Ce3+ to Tb3+ is about 55%. The fluorescence lifetime increases with the increase of Ce3+ and Tb3+ concentration, and the fluorescence lifetime of h-BN:0.025Tb3+, 0.05Ce3+ phosphor reached 2.087 ms. Additionally, the h-BN:0.025Tb3+, 0.05Ce3+ phosphor exhibits excellent thermal performance with an activation energy value of 0.2825 eV. Moreover, the photoluminescence quantum yield of the sample exceeds 52%. Therefore, the h-BN:Tb3+, Ce3+ samples can be used as green phosphors for solid state lighting and fluorescent labeling.

Two Purely Inorganic Cationic Tellurite Materials Based on Group IB Metal Tetrafluoroborates with Similar Lamellar Cationic Layers: [Cu2F(Te2O5)](BF4) and [Ag18O2(Te4O9)4(Te3O8)(BF4)2]·2HBF4.

Two new purely inorganic cationic tellurite networks of Group IB metal-based tetrafluoroborates, namely, [Cu2F(Te2O5)](BF4), 1, and [Ag18O2(Te4O9)4(Te3O8)(BF4)2]·2HBF4, 2, have been hydrothermally synthesized under mild conditions. The prepared materials have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR and Raman spectroscopy, SEM-energy-dispersive spectroscopy, UV-vis-NIR diffuse reflectance, magnetic study, and TG analyses. Single-crystal diffraction studies show that both materials have similar cationic Cu/Ag tellurite layers with tetrafluoroborates as interlamellar charge-balancing anions. Magnetic results indicate that [Cu2F(Te2O5)](BF4), 1, exhibits a mainly short-range antiferromagnetic ordering within the 2D layer, and further detailed analysis of magnetic susceptibility analysis confirms a spin-singlet ground state with an energy gap of 85 K.

Mild Periodic Acid Flux and Hydrothermal Methods for the Synthesis of Crystalline f-Element-Bearing Iodate Compounds.

f-element-bearing iodate compounds are a large family mostly synthesized by hydrothermal reactions starting with actinide/lanthanide ions and iodic acid or iodate salt. In this work, we introduce melting periodic acid flux as a new reaction medium and provide a safe way for single-crystal growth of a series of new f-element iodate compounds including UO2(IO3)2·H2O (1), UO2(IO3)2(H2O)·HIO3 (2), α-Th(IO3)2(NO3)(OH) (3), ß-Th(IO3)2(NO3)(OH) (4), and (H3O)9Nd9(IO3)36·3HIO3 (5). The structures of these compounds deviate from those afforded from hydrothermal reactions. Specifically, compounds 1 and 2 exhibit pillared structures consisting of uranyl pentagonal bipyramids and iodate trigonal pyramids. Compounds 3 and 4 represent two new thorium iodate compounds that are constructed from subunits of thorium dimers. Compound 5 exhibits a flower-shaped trivalent lanthanide iodate structure with HIO3 molecules and H3O+ cations filled in the channels. The aliovalent replacement of f elements in 5 is available from a hydrothermal process, further generating compounds of Th2(IO3)8(H2O) (6) and Ce2(IO3)8(H2O) (7). The distinct absorption features are observed in isotypic compounds 5-7, where 7 shows typical semiconductor behavior with a band gap of 2.43 eV. Remarkably, noncentrosymmetric 1, 6, and 7 exhibit strong second-harmonic-generation efficiencies of 1.3, 3.2, and 9.2 times, respectively, that of the commercial material KH2PO4. Additionally, the temperature-dependent emission spectra of 1 and 2 were also collected showing typical emission features of uranyl units and a negative correlation between the intensities of the emissions with temperature. Clearly, the presented low-temperature melting inorganic acid flux synthesis would provide a facile and effective strategy to produce a large new family of structurally versatile and multifunctional f-element inorganic compounds.

Systematic Investigation of the in Situ Reduction Process from U(VI) to U(IV) in a Phosphonate System under Mild Solvothermal Conditions.

The oxidation state greatly affects the chemical behavior of uranium in the nuclear fuel cycle and in the environment. Phosphonate ligands, on the other hand, show strong complexation toward uranium at different oxidation states and are widely used in nuclear fuel reprocessing. Therefore, in this work, the reduction behavior of U(VI) with the presence of a phosphonate ligand is investigated under mild solvothermal conditions. By adjusting the reaction time, temperature, and counterion species, a series of uranium diphosphonates including two U(VI), seven U(IV), two mixed-valent U(IV/VI), and one distinct U(IV/V/VI) compounds were obtained. All these compounds were characterized by single crystal X-ray diffraction and UV-vis-NIR absorption and fluorescence spectroscopy. The structural diversity among those compounds not only illustrates the intrinsic structural complexity in this system, but also illuminates the in situ reduction pathways that are affected by the variation of reaction conditions. The UV-vis-NIR absorption spectra of the tetravalent uranium compounds show that the absorption features are closely related to the local coordination environments of the uranium centers as well as the bonding modes of the phosphonate ligand. The fluorescence spectra of mixed-valent uranium compounds show unique emission features of U(VI) luminescence that are partially quenched by the multiple electronic transitions of U(IV) centers in the visible and NIR regions.

Surprising coordination for low-valent actinides resembling uranyl(vi) in thorium(iv) organic hybrid layered and framework structures based on a graphene-like (6,3) sheet topology.

Three thorium(iv)-based metal-organic hybrid compounds with 2D layered and 3D framework structures exhibiting graphene-like (6,3) sheet topologies were prepared with linkers with threefold symmetry. These compounds contain rare and relatively anisotropic coordination environments for low-valent actinides that are similar to those often observed for high-valent actinide ions.

Centrosymmetric and chiral porous thorium organic frameworks exhibiting uncommon thorium coordination environments.

The solvothermal reaction of thorium nitrate and tris-(4-carboxylphenyl)phosphine oxide in DMF affords a centrosymmetric porous thorium organic framework compound [Th(TPO)(OH)(H2O)]·8H2O (1). In contrast, the ionothermal reaction of the same reagents in the ionic liquid 1-butyl-2,3-dimethylimidazolium chloride results in the formation of a rare example of a chiral and porous thorium organic framework compound, [C9H17N2][Th(TPO)Cl2]·18H2O (2), which is derived solely from achiral starting materials. The geometries of the Th(iv) centers in compounds 1 and 2 are both atypical for low valent actinides, which can be best described as a ten-coordinate spherical sphenocorona and an irregular muffin, respectively. A large cavity of 17.5 Å (max. face to face) × 8 Å (min. face to face) with a BET surface area of 623 m(2) g(-1) in compound 2 is observed. The poor stability indicated by thermal gravimetric analysis and the water-resistance test for compound 2 may be due to the unique anisotropic coordination geometry for thorium. Temperature-dependent luminescence studies for both compounds indicate that the trends in the intensity vary as the Th-Th distance and the coordination environments of Th(iv) centers change.

Hybrid uranium-transition-metal oxide cage clusters.

Transition-metal based polyoxometalate clusters have been known for decades, whereas those built from uranyl peroxide polyhedra have more recently emerged as a family of complex clusters. Here we report the synthesis and structures of six nanoscale uranyl peroxide cage clusters that contain either tungstate or molybdate polyhedra as part of the cage, as well as phosphate tetrahedra. These transition-metal-uranium hybrid clusters exhibit unique polyhedral connectivities and topologies that include 6-, 7-, 8-, 10-, and 12-membered rings of uranyl polyhedra and uranyl ions coordinated by bidentate peroxide in both trans and cis configurations. The transition-metal polyhedra appear to stabilize unusual units built of uranyl polyhedra, rather than templating their formation.

Copper(I) and copper(II) uranyl heterometallic hybrid materials.

Two copper-uranium heterometallic compounds, [(UO2)3Cu(II)O2(C6NO2)5] (1) and [(UO2)Cu(I)(C6NO2)3] (2), have been synthesized by the reaction of uranyl acetate with copper salts in the presence of isonicotinic acid. Both compounds have been characterized by single-crystal X-ray diffraction, IR, Raman, and UV-vis spectroscopy. In compound 1, interactions between copper and uranium centers occur and result in a three-dimensional pillar layered structure. Compound 1 is also the first example of a heterometallic uranyl organic framework with a trinuclear U3O18 building block. Compound 2 is the first uranyl organic framework that contains monovalent copper, which arises from the reaction of Cu(II) chloride and is assumed to be due to the oxidation of chloride at low pH.

Synthesis of a uranyl persulfide complex and quantum chemical studies of formation and topologies of hypothetical uranyl persulfide cage clusters.

The compound Na(4)[(UO(2))(S(2))(3)](CH(3)OH)(8) was synthesized at room temperature in an oxygen-free environment. It contains a rare example of the [(UO(2))(S(2))(3)](4-) complex in which a uranyl ion is coordinated by three bidentate persulfide groups. We examined the possible linkage of these units to form nanoscale cage clusters analogous to those formed from uranyl peroxide polyhedra. Quantum chemical calculations at the density functional and multiconfigurational wave function levels show that the uranyl-persulfide-uranyl, U-(S(2))-U, dihedral angles of model clusters are bent due to partial covalent interactions. We propose that this bent interaction will favor assembly of uranyl ions through persulfide bridges into curved structures, potentially similar to the family of nanoscale cage clusters built from uranyl peroxide polyhedra. However, the U-(S(2))-U dihedral angles predicted for several model structures may be too tight for them to self-assemble into cage clusters with fullerene topologies in the absence of other uranyl-ion bridges that adopt a flatter configuration. Assembly of species such as [(UO(2))(S(2))(SH)(4)](4-) or [(UO(2))(S(2))(C(2)O(4))(4)](4-) into fullerene topologies with ~60 vertices may be favored by use of large counterions.

(UO2)2[UO4(trz)2](OH)2: a U(VI) coordination intermediate between a tetraoxido core and a uranyl ion with cation-cation interactions.

A uranyl triazole (UO(2))(2)[UO(4)(trz)(2)](OH)(2) (1) (trz = 1,2,4-triazole) was prepared using a mild solvothermal reaction of uranyl acetate with 1,2,4-triazole. Single-crystal X-ray diffraction analysis of 1 revealed it contains sheets of uranium-oxygen polyhedra and that one of the U(VI) cations is in an unusual coordination polyhedron that is intermediate between a tetraoxido core and a uranyl ion. This U(VI) cation also forms cation-cation interactions (CCIs). Infrared, Raman, and XPS spectra are provided, together with a thermogravimetric analysis that demonstrates breakdown of the compound above 300 °C. The UV-vis-NIR spectrum of 1 is compared to those of another compound that has a range of U(VI) coordination enviromments.

Glycine-templated manganese sulfate with new topology and canted antiferromagnetism.

A new glycine-templated manganese(II) sulfate, (C(2)NO(2)H(5))MnSO(4) (1), has been solvothermally synthesized and characterized crystallographically and magnetically. Crystal data for 1: monoclinic, space group P2(1)/m, a = 4.8884(10) A, b = 7.8676(14) A, c = 8.0252(15) A, beta = 106.524(2) degrees , V = 295.90(10) A(3), Z = 2. The glycine bridges Mn(II) ions in mu(2) mode and sulfate in eta(3),mu(4) mode. Along the b direction, the neighboring Mn(II) ions were bridged to each other by two sulfate ions and one glycine ligand to form a triple-stranded braid. The adjacent braids were connected via the sulfate ions to give a two-dimensional framework with a novel binodal 4,6-connected (3(2);4(2);5(2))(3(4);4(4);5(4);6(3)) topology. The compound exhibits a spin-canted antiferromagnetic behavior with a weak ferromagnetic transition below 9 K, and the estimated canting angle is 0.13 degrees.

A novel three-dimensional coordination polymer: poly[di-mu3-acetato-di-mu2-acetato-di-mu3-hydroxido-octa-mu3-triazolato-heptamanganese(II)].

The title compound, [Mn7(C2H2N3)8(C2H3O2)4(OH)2]n, is composed of centrosymmetric heptanuclear building units with the central Mn atom on an inversion center. In the building block, three Mn(II) ions are held together by one mu3-hydroxide group, two mu2-triazolate (trz) ligands and two mu2-acetate groups, forming an Mn3 cluster. Two Mn3 clusters are bridged by an Mn atom via two mu2-trz ligands and two mu2-O atoms from two acetate ions to construct a heptanuclear building block. The heptanuclear building units, lying parallel to each other along the b direction, form one-dimensional ladder-like chains and are further interlinked, resulting in a three-dimensional framework through Mn-N(trz) bonds.