M3(P2O7)22–-Type Open Frameworks Featuring [M2O8] and [M3O12] Multinuclear Transition-Metal Oxide Units. Serendipitous Synthesis of Six Polymorphic Salt-Inclusion Magnetic Solids: Na2M3(P2O7)2·ACl (M = Mn, Fe; A = Rb, Cs) and K2M3(P2O7)2·CsCl (M = Fe, Mn)

Reactivity of FeMoO4 in CsCl Fluxes and Formation of the Salt-Inclusion Type of Compounds

The reactivity of FeMoO₄ in CsCl fluxes has been investigated by thermal analysis and chemical reactions in evacuated silica ampules. The products have been characterized by ex situ X-ray diffraction methods. Metathesis reactions involving CsCl lead to the formation of Cs₂Fe₂(MoO₄)₃ and the salt adduct Cs₂FeCl₄·CsCl. A side reaction has been observed, which is associated with a decomposition of [MoO₄]^2- in CsCl fluxes yielding Cs₂Mo₂O₇·CsCl, which contains the rare pyromolybdate anion, [Mo₂O₇]^2-, located in the center of a _∞²[CsCl] hetero-honeycomb arrangement. This salt-inclusion type of compound has been studied further in terms of its formation starting from Cs₂MoO₄, MoO₃, and CsCl. The intermediate adduct phase, Cs₂MoO₄·MoO₃, contains uncharged _∞¹[MoO₂O_2/2] chains that react with CsCl at elevated temperatures to Cs₂Mo₂O₇·CsCl. Furthermore, the site preference for alkaline-metal cations (K⁺, Rb⁺, and Cs⁺) has been evaluated for a mixed substitution series. In accordance with the Pearson concept, the polarizability of the respect cation outweighs any size differences for the occupancy of the salt-intergrowth motif, the honeycomb part of the structure.

Targeted crystal growth of uranium gallophosphates via the systematic exploration of the UF4–GaPO4–ACl (A = Cs, Rb) phase space

The flux synthesis of a uranium gallophosphate and a uranium gallate, Cs₄[UO₂Ga₂(PO₄)₄] and Cs₂UO₂Ga₂O₅, and 4 uranium phosphates, [Rb₂Rb_3.93Cl_0.93][(UO₂)₅(PO₄)₅], Rb₁₁[(UO₂)₈(PO₄)₉], Rb_7.6[(UO₂)₈O_8.6F_0.4(PO₄)₂], and Rb₆[(UO₂)₅O₂(PO₄)₄], is reported.

Single crystal neutron and magnetic measurements of Rb2Mn3(VO4)2CO3 and K2Co3(VO4)2CO3 with mixed honeycomb and triangular magnetic lattices

Two new alkali vanadate carbonates with divalent transition metals have been synthesized as large single crystals via a high-temperature (600 °C) hydrothermal technique. Compound I, Rb2Mn3(VO4)2CO3, crystallizes in the trigonal crystal system in the space group P3[combining macron]1c, and compound II, K2Co3(VO4)2CO3, crystallizes in the hexagonal space group P63/m. Both structures contain honeycomb layers and triangular lattices made from edge-sharing MO6 octahedra and MO5 trigonal bipyramids, respectively. The honeycomb and triangular layers are connected along the c-axis through tetrahedral [VO4] groups. The MO5 units are connected with each other by carbonate groups in the ab-plane by forming a triangular magnetic lattice. The difference in space groups between I and II was also investigated with Density Functional Theory (DFT) calculations. Single crystal magnetic characterization of I indicates three magnetic transitions at 77 K, 2.3 K, and 1.5 K. The corresponding magnetic structures for each magnetic transition of I were determined using single crystal neutron diffraction. At 77 K the compound orders in the MnO6-honeycomb layer in a Néel-type antiferromagnetic orientation while the MnO5 triangular lattice ordered below 2.3 K in a colinear 'up-up-down' fashion, followed by a planar 'Y' type magnetic structure. K2Co3(VO4)2CO3 (II) exhibits a canted antiferromagnetic ordering below TN = 8 K. The Curie-Weiss fit (200-350 K) gives a Curie-Weiss temperature of -42 K suggesting a dominant antiferromagnetic coupling in the Co2+ magnetic sublattices.

Synthesis, structure and magnetic behavior of iron arsenites with hierarchical magnetic units

Iron-arsenites may cover multiple Fe oxidation states, while the versatile (AsO₃)²⁻ condensation offer ideal spacers between magnetic sub-units with various dimensionalities (D). We show here four novel compounds covering the 0–3D magnetic panorama.

Overstepping Löwenstein's Rule-A Route to Unique Aluminophosphate Frameworks with Three-Dimensional Salt-Inclusion and Ion-Exchange Properties

The synthesis of four non-Löwenstein uranyl aluminophosphates, [Cs₁₃Cl₅][(UO₂)₃Al₂O(PO₄)₆], Rb₇[Al₂O(PO₄)₃][(UO₂)₆O₄(PO₄)₂], Cs₃[Al₂O(PO₄)₃][(UO₂)₃O₂], and Rb₃[Al₂O(PO₄)₃][(UO₂)₃O₂], the first uranyl phosphate salt-inclusion material [Cs₄Cs₄Cl][(UO₂)₄(PO₄)₅], and a related structure Cs₄[UO₂Al₂(PO₄)₄], all prepared by molten flux methods, is reported. All compounds are discussed from the point of view of their structural features favoring, in some cases, ion-exchange properties. Löwenstein's rule, well known in the realm of zeolites, aluminosilicate, and aluminophosphate minerals, describes the tendency of tetrahedra (Al, P, Si, and Ge) linked by an oxygen bridge to be of two different elements resulting in the avoidance of Al-O-Al bonds. Zeolites and related aluminosilicate/aluminophosphate minerals are traditionally formed under relatively mild temperatures, where zeolites are synthesized using the hydrothermal synthetic technique. Few exceptions to Löwenstein's rule are known among aluminophosphates, and four of the five exceptions are synthesized under either high temperature or high pressure methods. For that reason, the high-temperature flux synthesis of four new non-Löwenstein uranyl aluminophosphates realizes a unique synthetic approach to forming the new pyroaluminate-based building block, [Al₂O(PO₄)₆]^14-, that can be easily obtained and employed for the construction of new porous structures.

A new polymorph of the common coformer isonicotinamide

A polymorph of the widely employed coformer isonicotinamide crystallizing in the space group Pca2₁ is described for the first time.

Understanding the Stability of Salt-Inclusion Phases for Nuclear Waste-forms through Volume-based Thermodynamics

Formation enthalpies and Gibbs energies of actinide and rare-earth containing SIMs with silicate and germanate frameworks are reported. Volume-based thermodynamics (VBT) techniques complemented by density functional theory (DFT) were adapted and applied to these complex structures. VBT and DFT results were in closest agreement for the smaller framework silicate structure, whereas DFT in general predicts less negative enthalpies across all SIMs, regardless of framework type. Both methods predict the rare-earth silicates to be the most stable of the comparable structures calculated, with VBT results being in good agreement with the limited experimental values available from drop solution calorimetry.

Synthesis and structural variety of first Mn and Bi selenites and selenite chlorides

Single crystals of new Mn2[Bi2O](SeO3)4 (I), MnBi(SeO3)2Cl (II), MnIIMnIII(SeO3)2Cl (III), Mn5(SeO3)2Cl6 (IV), and Mn4(Mn5,Bi)(SeO3)8Cl5 (V) have been synthesized by chemical vapour transport and hydrothermal methods. They have been structurally characterized by single crystal X-ray diffraction analysis. The compounds II–V are the first Mn selenite chlorides, while the I, II and V compounds are the first Bi-containing Mn oxoselenites. Structural relationships of the new phases with other compounds are discussed. An overview of the mixed-ligand MnO m Cl n polyhedra in inorganic compounds is given.

Two halide-containing cesium manganese vanadates: synthesis, characterization, and magnetic properties

Two new halide-containing cesium manganese vanadates have been synthesized by a high-temperature (580 °C) hydrothermal synthetic method from aqueous brine solutions.

The synthesis, structure and properties of a new lithium-rich manganese(ii) phosphate Li5CsMn(P2O7)2: a congruently melting compound with a 'lithium hamburger' structure

The crystals of the title compound have been grown in molten salt media. Single-crystal X-ray diffraction experiment revealed that the compound crystallizes in an orthorhombic space group Pbcn (no. 60) with cell parameters: a = 5.1023(10) Å, b = 19.717(4) Å, c = 12.557(3) Å, and Z = 4. The structure of Li5CsMn(P2O7)2 consists of one-dimensional manganese pyrophosphate chains [MnP4O14]∞ interleaved with Cs(+) and Li(+) cations. A pseudo-two-dimensional layer [CsMnP4O14]∞ parallel to the ab plane is made up of [MnP4O14]∞ chains and Cs-O polyhedra through sharing the oxygen atoms. The three crystallographically distinct Li atoms are all located in the interlayered space to form a 'lithium hamburger' structure. Magnetic studies demonstrated that the compound shows paramagnetic behavior. DSC and XRD investigations revealed that the compound melts congruently. AC impedance studies show that the conductivity is 1.3 × 10(-5) S cm(-1) at 573 K and the activation energy is 0.42 eV. In addition, Li ion diffusional pathways were obtained using the bond valence map.