Synthesis, Structures, and Magnetic Investigations of Nickel Phosphates: Ni2(PO4)(OH), Ni7(PO4)3(HPO4)(OH)3, and NaNiPO4 Including Potential Haldane Behavior.

Three novel nickel-phosphate structures are reported, Ni2(PO4)(OH) (I), Ni7(PO4)3(HPO4)(OH)3 (II), and NaNiPO4 (III). Each new system was prepared via a high-temperature hydrothermal synthesis at 600-650 °C. All three compounds are built of quasi-one-dimensional (quasi-1-D) Ni2+ containing chains with varying phosphate bridging modes and were characterized by single crystal X-ray diffraction and magnetic susceptibility. All three compounds display very different magnetic behavior. Anisotropic magnetic data is reported for Ni2(PO4)(OH) (I) exhibiting slow antiferromagnetic ordering in the high-temperature regime with substructures that begin to form below 32 K at different field strengths. These characteristics affirm I as being one of the few Haldane-like material candidates. The Ni7(PO4)3(HPO4)(OH)3 (II) material is a member of the unusual ellenbergerite structural family and displays complex inter- and intrachain magnetic interactions while NaNiPO4 (III) shows antiferromagnetic ordering near 18 K. This magnetic behavior is correlated with their structures.

Alkali Transition-Metal Molybdates: A Stepwise Approach to Geometrically Frustrated Systems.

Materials with triangular arrangements of transition metal ions are of great interest for their complex magnetism resulting from geometric frustration. This paper describes the stepwise formation of kagome lattices of open shell transition-metal ions from half-delta chains to delta/sawtooth chains, and finally kagome nets. The systems can be viewed as a testbed for magnetic studies since a variety of spin states can be introduced across the same structure type, and progress through increasing levels of structural complexity and dimensionality. The synthetic and structural development of this continuum is studied here in well-formed single crystals of A2 M3 (MoO4 )3 (OH)2 (A=K, Rb; M=Mn, Co), CsM2 (MoO4 )2 (OH) (M=Mn, Fe, Co, Zn), and KM3 (MoO4 )2 O(OH) (M=Mn).

Chemistry of Metal Silicates and Germanates: The Largest Metal Polygermanate, K11Mn21Ge32O86(OH)9(H2O), with a 76 Å Periodic Lattice.

An examination of manganese silicates and germanates revealed unusual structural motifs and extremely different chemistries, with identical hydrothermal reactions forming K2Mn2Si3O9 versus K11Mn21Ge32O86(OH)9(H2O). The germanate is exceptional in both its c-axis length (exceeding 76 Å) and unit cell volume (nearly 18000 Å3), the largest known polygermanate structure to our knowledge.

Observation of a Large Magnetic Anisotropy and a Field-Induced Magnetic State in SrCo(VO4)(OH): A Structure with a Quasi One-Dimensional Magnetic Chain.

A new member of the descloizite family, a cobalt vanadate, SrCo(VO4)(OH), has been synthesized as large single crystals using high-temperature and high-pressure hydrothermal methods. SrCo(VO4)(OH) crystallizes in the orthorhombic crystal system in space group P212121 with the following unit cell parameters: a = 6.0157(2) Å, b = 7.645(2) Å, c = 9.291(3) Å, V = 427.29(2) Å3, and Z = 4. It contains one-dimensional Co-O-Co chains of edge-sharing CoO6 octahedra along the a-axis connected to each other via VO4 tetrahedra along the b-axis forming a three-dimensional structure. The magnetic susceptibility of SrCo(VO4)(OH) indicates an antiferromagnetic transition at 10 K as well as unusually large spin orbit coupling. Single-crystal magnetic measurements in all three main crystallographic directions displayed a significant anisotropy in both temperature- and field-dependent data. Single-crystal neutron diffraction at 4 K was used to characterize the magnetically ordered state. The Co2+ magnetic spins are arranged in a staggered configuration along the chain direction, with a canting angle that follows the tipping of the CoO6 octahedra. The net magnetization along the chain direction, resulting in ferromagnetic coupling of the a-axis spin components in each chain, is compensated by an antiferromagnetic interaction between nearest neighbor chains. A metamagnetic transition appears in the isothermal magnetization data at 2 K along the chain direction, which seems to correspond to a co-alignment of the spin directions of the nearest neighbor chain. We propose a phenomenological spin Hamiltonian that describes the canted spin configuration of the ground state and the metamagnetic transition in SrCo(VO4)(OH).

Organic Fluorophore Coated Polycrystalline Ceramic LSO:Ce Scintillators for X-ray Bioimaging.

The current effort demonstrates that lutetium oxyorthosilicate doped with 1-10% cerium (Lu2SiO5:Ce, LSO:Ce) radioluminescent particles can be coated with a single dye or multiple dyes and generate an effective energy transfer between the core and dye(s) when excited via X-rays. LSO:Ce particles were surface modified with an alkyne modified naphthalimide (6-piperidin-1-yl-2-prop-2-yn-1-yl-1 H-benzo[ de]isoquinoline-1,3-(2 H)-dione, AlNap) and alkyne modified rhodamine B ( N-(6-diethylamino)-9-{2-[(prop-2-yn-1-yloxy)carbonyl]phenyl}-3 H-xanthen-3-ylidene)- N-ethylethanaminium, AlRhod) derivatives to tune the X-ray excited optical luminescence from blue to green to red using Förster Resonance Energy Transfer (FRET). As X-rays penetrate tissue much more effectively than UV/visible light, the fluorophore modified phosphors may have applications as bioimaging agents. To that end, the phosphors were incubated with rat cortical neurons and imaged after 24 h. The LSO:Ce surface modified with AlNap was able to be successfully imaged in vitro with a low-output X-ray tube. To use the LSO:Ce fluorophore modified particles as imaging agents, they must not induce cytotoxicity. Neither LSO:Ce nor LSO:Ce modified with AlNap showed any cytotoxicity toward normal human dermal fibroblast cells or mouse cortical neurons, respectively.

Magnetic Ground State Crossover in a Series of Glaserite Systems with Triangular Magnetic Lattices.

The magnetic properties are reported for three members of the glaserite series of compounds, Na2BaM(VO4)2, M = Mn, Mn0.6Co0.4, and Co. Large single crystals are grown using a high-temperature hydrothermal synthesis method. This structure type exhibits a triangular magnetic lattice in which M2+O6 octahedra are interconnected with nonmagnetic (VO4)3- groups. All the structures crystallize at room temperature with rigid trigonal symmetry (space group P3̅ m1); however, at lower temperatures both Na2BaMn(VO4)2 and Na2BaMn0.6Co0.4(VO4)2 undergo a structural transition to lower symmetry (monoclinic, C2/ c). The bulk magnetic measurements indicate that Mn- and Co-structures are antiferromagnetic and ferromagnetic, respectively. Na2BaMn0.6Co0.4(VO4)2 does not show any long-range ordering down to 0.5 K, although a broad heat capacity anomaly near 1.2 K suggests short-range magnetic order or freezing into a spin-glass-like state related to the chemical disorder and resulting competing magnetic interactions. The magnetic structures of Na2BaMn(VO4)2 and Na2BaCo(VO4)2 were determined using neutron powder diffraction. At zero magnetic field, Na2BaMn(VO4)2 possesses an antiferromagnetic structure with the moments ordered in a Néel-type arrangement and aligned along the C4 axis of the octahedra. Under applied magnetic field at 0.3 K, the evolution of the magnetic structure toward a fully polarized state is observed. Na2BaCo(VO4)2 represents a ferromagnetic (FM) magnetic structure with Co moments aligned parallel to the c-axis direction. The relationships between these structures and magnetic properties are discussed.

Single Crystals of Cubic Rare-Earth Pyrochlore Germanates: RE2Ge2O7 (RE = Yb and Lu) Grown by a High-Temperature Hydrothermal Technique.

Large single crystals of Yb2Ge2O7 in the cubic Fd3̅ m space group, are synthesized and characterized from a high-temperature hydrothermal method (650°C/200 MPa in 1 M KF). The cubic phase displays spin frustration and possibly nonclassical quantum-spin behavior at low temperature. This is the first report of single crystals of this important phase of size and quality suitable for single-crystal neutron diffraction.

A Cesium Rare-Earth Silicate Cs3 RESi6 O15 (RE=Dy-Lu, Y, In): The Parent of an Unusual Structural Class Featuring a Remarkable 57†ŠUnit Cell Axis.

The structure of Cs3 RESi6 O15 , where RE=Dy-Lu, Y, In, is unusual in that it contains octahedrally coordinated rare-earth ions; their relative orientation dictates the structure, as they rotate about the c-axis supported by the cyclic Si6 O15 framework. The repeat unit of the rotation is eight units generating a very long (ca. 57 Å) unit cell axis. This unusual repeat unit is created by the structural flexibility of the hexasilicate ring, which is in turn affected by the size of the rare earth ion as well as the size of alkali ion residing within the silicate layers. Previous work showed for the smaller Sc3+ ion, the rotation of the octahedra is not sufficient to achieve closure at an integral repeat unit and an incommensurate structure results. The products are prepared as large, high quality single crystals using a high-temperature (650 °C) hydrothermal method with CsOH and F- mineralizers. The presence of fluoride is essential to the formation of the product.

Three Unique Barium Manganese Vanadates from High-Temperature Hydrothermal Brines.

Three new barium manganese vanadates, all containing hexagonal barium chloride layers interpenetrated by [V2O7]4- groups, were synthesized using a high-temperature (580 °C) hydrothermal method. Two of the compounds were prepared from a mixed BaCl2/Ba(OH)2 mineralizer, and the third compound was prepared from BaCl2 mineralizer. An interesting structural similarity exists between two of the compounds, Ba2Mn(V2O7)(OH)Cl and Ba4Mn2(V2O7)(VO4)2O(OH)Cl. These two compounds crystallize in the orthorhombic space group Pnma, Z = 4, and are structurally related by a nearly doubled a axis. The first structure, Ba2Mn(V2O7)(OH)Cl (I) (a = 15.097(3) Å, b = 6.1087(12) Å, c = 9.5599(19) Å), consists of octahedral manganese(II) edge-sharing chains linked by pyrovanadate [V2O7] groups, generating a three-dimensional structure. Compound II, Ba4Mn2(V2O7)(VO4)2O(OH)Cl (a = 29.0814(11) Å, b = 6.2089(2) Å, c = 9.5219(4) Å), is composed of manganese(III) edge-sharing chains that are coordinated to one another through pyrovanadate groups in a nearly identical way as in I, forming a zigzag layer. A key difference in II is that these layers are capped on either end by two monomeric [VO4] groups that directly replace one [V2O7] group in I. The third compound, Ba5Mn3(V2O7)3(OH,Cl)Cl3 (III), crystallizes in the trigonal space group R32 (a = 9.7757(4) Å, c = 22.4987(10) Å) and is composed of manganese(II) trimeric units, [Mn3O12(OH,Cl)], coordinated to one another through pyrovanadate [V2O7] groups to form a three-dimensional structure. The unusual manganese trimers are built of three square pyramids all linked by a central (OH/Cl) atom. The key factor directing the formation of the different structures appears to be the identity and concentration of the halide brine mineralizer fluid. The ability of such brines to induce the formation of interpenetrated salt lattices in the present study is suggestive of a versatile realm of descriptive synthetic inorganic chemistry.

Investigation of a Structural Phase Transition and Magnetic Structure of Na2BaFe(VO4)2: A Triangular Magnetic Lattice with a Ferromagnetic Ground State.

The structural and magnetic properties of a glaserite-type Na2BaFe(VO4)2 compound, featuring a triangular magnetic lattice of Fe2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal P3̅m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (Ts = 288 K). This structural transition involves a tilting of Fe-O-V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na2BaFe(VO4)2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Overall, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO6 octahedron.

One-Pot Hydrothermal Synthesis of TbIII13(GeO4)6O7(OH) and K2TbIVGe2O7: Preparation of a Stable Terbium(4+) Complex.

Two terbium germanates have been synthesized via high-temperature and high-pressure hydrothermal synthesis with 20 M KOH as a mineralizer using Tb4O7 as a starting material. Tb13(GeO4)6O7(OH) crystallizes in trigonal space group R3̅, is built up of isolated GeO4 units, and contains a complex arrangement of terbium oxide polyhedra. K2TbGe2O7 is a terbium(4+) pyrogermanate that is isostructural with K2ZrGe2O7 and displays a rare stable Tb4+ oxidation state in the solid state.

Manganese Vanadate Chemistry in Hydrothermal BaF2 Brines: Ba3Mn2(V2O7)2F2 and Ba7Mn8O2(VO4)2F23.

Manganese vanadate fluorides were synthesized using high-temperature hydrothermal techniques with BaF2 as a mineralizer. Ba3Mn2(V2O7)2F2 crystallizes in space group C2/c and consists of dimers built from edge-sharing MnO4F2 trigonal prisms with linking V2O7 groups. Ba7Mn8O2(VO4)2F23 crystallizes in space group Cmmm, with a manganese oxyfluoride network built from edge- and corner-sharing Mn2+/3+(O,F)6 octahedra. These octahedra form alternating Mn2+ and Mn2+/3+ layers separated by VO4 tetrahedra. This latter compound exhibits a canted antiferromagnetic order below TN = 25 K.

Honeycomb-like S = 5/2 Spin-Lattices in Manganese(II) Vanadates.

New complex manganese vanadate materials were synthesized as high-quality single crystals in multi-millimeter lengths using a high-temperature, high-pressure hydrothermal method. One compound, Mn5(VO4)2(OH)4, was grown from Mn2O3 and V2O5 in 3 M CsOH at 580 °C and 1.5 kbar. Changing the mineralizer to 1 M CsOH/3MCsCl leads to the formation of another product, Mn6O(VO4)2(OH). Both compounds were structurally characterized by single-crystal X-ray diffraction (Mn5(VO4)2(OH)4: C2/m, Z = 2, a = 9.6568(9) Å, b = 9.5627(9) Å, c = 5.4139(6) Å, ß = 98.529(8)°; Mn6O(VO4)2(OH): P21/m, Z = 2, a = 8.9363(12) Å, b = 6.4678(8) Å, c = 10.4478(13) Å, ß = 99.798(3)°), revealing interesting low-dimensional transition-metal features. Mn5(VO4)2(OH)4 possesses complex honeycomb-type Mn-O layers, built from edge-sharing [MnO6] octahedra in the bc plane, with bridging vanadate groups connecting these layers along the a-axis. Mn6O(VO4)2(OH) presents a more complicated structure with both octahedral [MnO6] and trigonal bipyramidal [MnO5] units. A different pattern of planar honeycomb sheets are formed by edge-shared [MnO6] octahedra, and these sublattices are connected through edge-shared dimers of [MnO5] trigonal bipyramids to form corrugated sheets. Vanadate groups again condense the sheets into a three-dimensional framework. Infrared and Raman spectroscopies indicated the presence of OH groups and displayed characteristic Raman scattering due to vanadate groups. Temperature-dependent magnetic studies indicated Curie-Weiss behavior above 100 K with significant anti-ferromagnetic coupling for both compounds, with further complex magnetic behavior at lower temperatures. The data indicate canted anti-ferromagnetic order below 57 K in Mn5(VO4)2(OH)4 and below 45 K in Mn6O(VO4)2(OH). Members of another class of compounds, K2M3(VO4)2(OH)2 (M = Mn, Co), also containing a honeycomb-type sublattice, were also synthesized to allow a comparison of the structural features across all three structure types and to demonstrate extension to other transition metals.

Hydrothermal Formation of Calcium Copper Tetrasilicate.

We describe the first hydrothermal synthesis of CaCuSi4 O10 as micron-scale clusters of thin platelets, distinct from morphologies generated under salt-flux or solid-state conditions. The hydrothermal reaction conditions are surprisingly specific: too cold, and instead of CaCuSi4 O10 , a porous calcium copper silicate forms; too hot, and calcium silicate (CaSiO3 ) forms. The precursors also strongly impact the course of the reaction, with the most common side product being sodium copper silicate (Na2 CuSi4 O10 ). Optimized conditions for hydrothermal CaCuSi4 O10 formation from calcium chloride, copper(II) nitrate, sodium silicate, and ammonium hydroxide are 350 °C at 3000 psi for 72 h; at longer reaction times, competitive delamination and exfoliation causes crystal fragmentation. These results illustrate that CaCuSi4 O10 is an even more unique material than previously appreciated.

Hydrothermal growth of lanthanide borosilicates: a useful approach to new acentric crystals including a derivative of cappelenite.

The reaction of barium borosilicate glasses in hydrothermal fluids with NaOH mineralizer at ca. 600-650 °C in the presence of various sources of Eu(3+) ions leads to a new series of noncentrosymmetric single crystals characterized by single-crystal X-ray diffraction. Under three slightly different reaction modifications, three new Eu(3+)-containing noncentrosymmetric single crystals were isolated and characterized. Using a barium borosolicate glass with Eu(2)O(3) added to the reaction mixture led to NaBaEuSi(3)O(9) (1), which crystallizes in the noncentrosymmetric orthorhombic space group P2(1)2(1)2(1) with unit cell parameters a = 5.6373(11) Å, b = 11.483(2) Å, and c = 12.535(2) Å and consists of Eu(3+) ions linked by Si(3)O(9)(6-) rings. Using a similar glass feedstock with Eu(3+) included in the starting glass composition led to the compound NaBa(3)Eu(3)Si(6)O(20) (2), which was determined in the noncentrosymmetric polar space group Ama2 with unit cell parameters a = 14.777(3) Å, b = 23.926(5) Å, and c = 5.5533(11) Å. It is constructed of individual islands of Si(4)O(13)(10-) and lone Si(2)O(7)(6-) building fragments. Finally, use of the Eu-containing glass along with additional Eu(2)O(3) led to the compound BaEu(6)(Si(3)B(6)O(24))(OH)2 (3), which crystallizes in the polar space group P6mm with a = 10.8074(15) Å and c = 4.7296(9) Å. It is related to the rare and poorly understood mineral cappelenite Ba(Y,RE)(6)(Si(3)B(6)O(24))F(2) and contains six-membered tetrahedral borate rings linked by silicate tetrahedra. The high percentage of noncentrosymmetric crystals obtained from of a simple borosilicate glass starting material, along with various straightforward chemical additives, suggests strongly that many more noncentrosymmetric crystals can be isolated from this general system.

Hydrothermal Synthesis and Characterization of Novel Brackebuschite-Type Transition Metal Vanadates: Ba2M(VO4)2(OH), M = V(3+), Mn(3+), and Fe(3+), with Interesting Jahn-Teller and Spin-Liquid Behavior.

A new series of transition metal vanadates, namely, Ba2M(VO4)2(OH) (M = V(3+), Mn(3+), and Fe(3+)), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba2V(VO4)2(OH) is monoclinic in space group P21/m, a = 7.8783(2) Å, b = 6.1369(1) Å, c = 9.1836(2) Å, ß = 113.07(3)°, V = 408.51(2) Å(3). The other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the b-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba2Mn(VO4)2(OH) analogue yielded a new understanding of the Jahn-Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Single-crystal temperature-dependent magnetic studies on Ba2V(VO4)2(OH) reveal a broad feature over a wide temperature range with maximum at ∼100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies.

Twinned caesium cerium(IV) penta-fluoride.

Single-crystals of CsCeF5 were synthesized hydro-thermally. The crystal under investigation was twinned by pseudo-merohedry with a twofold rotation around the c axis as an additional twinning operation. The crystal structure is built of layers of distorted edge- and corner-sharing CeF8 square-anti-prisms. The Cs(+) cations are located between the layers and exhibit coordination numbers of nine. Upon compression, CsCeF5 undergoes an irreversible phase transition at about 1 GPa.

Large magnetic anisotropy of a decorated spin-chain system K2Co3(MoO4)3(OH)2.

The magnetic structure of K2Co3(MoO4)3(OH)2 is studied in detail. The material has a half-sawtooth one-dimensional (1-D) structure containing two unique Co2+ ions, one in the chain backbone and one on the apex of the sawtooth creating a series of isosceles triangles along the b-axis. These triangles can be a source of magnetic frustration. The ability to grow large single crystals enables detailed magnetic measurements with the crystals oriented in a magnetic field along the respective axes. It has a Curie-Weiss temperature θCW of 5.3(2) K with an effective magnetic moment of 4.8(3)µB/Co. The material is highly anisotropic with a sharp antiferromagnetic ordering transition at 7 K with a metamagnetic transition at 2 kOe. Neutron diffraction was used to determine the magnetic structure and revealed a magnetic structure with canted spins along the backbone of the chain while spins along the sawtooth caps maintained a colinear orientation, arranging antiferromagnetically relative to the backbone spins. The parallel chains arrange antiferromagnetically relative to each other along the c-axis and ferromagnetically along the a-axis.

Hydrothermal chemistry, structures, and luminescence studies of alkali hafnium fluorides.

This paper describes the hydrothermal chemistry of alkali hafnium fluorides, including the synthesis and structural characterization of five new alkali hafnium fluorides. Two ternary alkali hafnium fluorides are described: Li(2)HfF(6) in space group P31m with a = 4.9748(7) Å and c = 4.6449(9) Å and Na(5)Hf(2)F(13) in space group C2/m with a = 11.627(2) Å, b = 5.5159(11) Å, and c = 8.4317(17) Å. Three new alkali hafnium oxyfluorides are also described: two fluoroelpasolites, K(3)HfOF(5) and (NH(4))(3)HfOF(5), in space group Fm3m with a = 8.9766(10) and 9.4144(11) Å, respectively, and K(2)Hf(3)OF(12) in space group R3m with a = 7.6486(11) Å and c = 28.802(6) Å. Infrared (IR) spectra were obtained for the title solids to confirm the structure solutions. Comparison of these materials was made based on their structures and synthesis conditions. The formation of these species in hydrothermal fluids appears to be dependent upon both the concentration of the alkali fluoride mineralizer solution and the reaction temperature. Both X-ray and visible fluorescence studies were conducted on compounds synthesized in this study and showed that fluorescence was affected by a variety of factors, such as alkali metal size, the presence/absence of oxygen in the compound, and the coordination environment of Hf(4+).

Hydrothermal synthesis and comparative coordination chemistry of new rare-earth V4+ compounds.

Several new hydrated rare earth vanadates and rare earth oxy-vanadates have been synthesized using hydrothermal techniques and characterized using single crystal and powder X-ray diffraction and infrared and UV-vis absorption spectroscopies. The hydrated rare earth vanadates adopt the space group P2(1)/m with general formula A(3)VO(5)(OH)(3) (A = Y (1), Dy (2), or La (3)) and contain anionic distorted square pyramidal [VO(5)](-6) units and AO(7) and AO(8) polyhedra. The oxy-vanadates with the general formula A(2)O(VO(4)) (A = Y (4), Dy (5; 6), or Yb (7)) form two polymorphs in either P2(1)/c or C2/c space groups and contain anionic tetrahedral [VO(4)](-4) units and nonvanadium bonded O(2-) anions in distorted [OA(4)] tetrahedra. In all cases, the vanadium ion is in the tetravalent oxidation state, and its original source was the trace V(4+) impurities in YVO(4). The observed vanadyl and equatorial vanadium-oxygen bond lengths about the square pyramid in compounds 1-3 and the tetrahedral vanadium coordination found in compounds 4-7 are unusual for V(4+). The electronic and vibrational spectra are also reported and correlated with the appropriate coordination environment.