A new family of mixed anion cesium rare earth silicates exhibiting intense scintillation in several ranges of the visible spectrum are reported. Cs3RESi4O10F2 (RE = Y, Eu–Lu) have been synthesized using an enhanced flux growth method for the targeted growth of mixed anion systems. This is the first example of this method being used for the growth of oxyhalides. The compounds crystallize in the triclinic space group P1̅ with the lattice parameters a = 7.0832(2) Å, b = 7.1346(2) Å, c = 16.2121(5) Å, α = 95.8090(10)°, β = 90.0580(10)°, γ = 119.7650(10)° for the Tb analogue. The structure consists of REO6 and REO2F4 polyhedra connected by Si4O10 sheets with a previously unobserved silicate sheet topology that contains the uncommon cyclic Si3O9 trimers. The synthesis, structure, magnetic and optical properties are reported including, notably, intense X-ray scintillation in Cs3TbSi4O10F2.

Single crystals of two new uranyl silicates were grown from mixed alkali fluoride/alkali chloride fluxes. Polymorphism is observed in Cs2(UO2)Si2O6, where hydrothermal conditions lead to the α polymorph and flux growth favors the β polymorph. Rb2(UO2)Si2O6 crystallizes in a monoclinic distortion of the α-Cs2(UO2)Si2O6 structure type with space group I2/a and lattice parameters a = 14.9932(5) Å, b = 14.8032(5) Å, c = 16.2377(9) Å, and β = 90.7220(10)°. β-Cs2(UO2)Si2O6 constitutes a new polymorph of Cs2(UO2)Si2O6 and crystallizes in the monoclinic space group C2 with lattice parameters a = 12.136(2) Å, b = 10.0426(17) Å, c = 7.7896(13) Å, and β = 95.849(4)°. The two structures are compared, the driving force behind the observed polymorphism is discussed, and the luminescence properties are reported for each compound.

•The fresnoite related Ba3Ti2Si4O14Cl0.91O0.09 were grown via molten flux method.•The in situ reduction of Ti(IV) to Ti(III) is achieved using metallic Mg.•2D layers of Ti2O9 and Si4O12 and Ti2O9Cl2 and Si2O7 connect via Ba atoms.•The magnetic susceptibility shows simple paramagnetism above 100 K.Single crystals of mixed valent barium titanium(III/IV) chlorosilicate, Ba3Ti2Si4O14Cl0.91O0.09, were grown in a high temperature molten chloride flux involving an in situ reduction step. The fresnoite structure related Ba3Ti2Si4O14Cl0.91O0.09 crystallizes in the tetragonal space group P4/mbm with lattice parameters of a=8.6717(2) Å, c=18.6492(5) Å. The title compound exhibits a 3D structure consisting of 2D layers of fused Ti2O9 and Si4O12 groups and 2D layers of fused Ti2O9Cl2 and Si2O7 groups that are linked via barium atoms. The in situ reduction of Ti(IV) to Ti(III) is achieved via the addition of metallic Mg to the flux to function as the reducing agent. The temperature dependence of the magnetic susceptibility shows simple paramagnetism above 100 K. There is a discontinuity in the susceptibility data below 100 K, which might be due to a structural change that takes place resulting in charge ordering.The fresnoite structure related novel reduced barium titanium chlorosilicate, Ba3Ti2Si4O14Cl0.91O0.09, were synthesized via flux method. An in situ reduction of Ti(IV) to Ti(III) achieved using Mg metal. The 3D structure consists 2D layers of fused Ti2O9 and Si4O12 and 2D layers of fused Ti2O9Cl2 and Si2O7 connected via barium atoms. Compound shows simple paramagnetism above 100 K.Download high-res image (456KB)Download full-size image

Single crystals of five transition metal uranium fluorides were obtained via the use of a mild hydrothermal route. Uranyl acetate was used as both the uranium source and the reducing agent for an in situ reduction of U(VI) to U(IV). The synthesized materials are present as both two- and three-dimensional structures and contain uranium in 9-fold coordination environments. Magnetic susceptibility measurements indicate that the reported materials remain paramagnetic down to 2 K, with no evidence for the existence of long-range magnetic ordering. Thermogravimetric analysis studies of the reported materials are also presented.

High quality single crystals of the monoclinic phase K5U5O17(OH) were synthesized via a hydrothermal method utilizing the supercritical regime of water. The structure of K5U5O17(OH) is isotypic with the Na phase, Na5U5O17(OH), however crystallizes in a slightly different space group due to size effects. K5U5O17(OH) has the same sheet-anion structure as the Na analog, whose topology is analyzed here for the first time. K5U5O17(OH) shows fluorescence typical for uranyl species.

Single crystals of Na3GaF6 were prepared via a mild hydrothermal method and the crystal structure was characterized by single crystal X-ray diffraction. Na3GaF6 crystallizes in the monoclinic space group P21/n with a = 5.4724(3) Å, b = 5.6742(3) Å, c = 7.8866(4) Å, γ = 90.361(1)˚, V = 244.89(2) Å3, and Z = 2. The compound exhibits a cryolite-type crystal structure consisting of corner-shared GaF6 and Na(1)O6 polyhedra. The Ga and Na(1) atoms are found in almost regular octahedra, whereas the Na(2) atom is observed in a highly distorted square antiprismatic coordination environment.The synthesis and crystal structure of the hexafluorogallate, Na3GaF6 is reported.

The noncentrosymmetric tungstate oxide, Ce18W10O57, was synthesized for the first time as high-quality single crystals via the molten chloride flux method and structurally characterized by single-crystal X-ray diffraction. The compound is a structural analogue to the previously reported La18W10O57, which crystallizes in the hexagonal space group P6̅2c. The +3 oxidation state of cerium in Ce18W10O57 was achieved via the in situ reduction of Ce(IV) to Ce(III) using Zn metal. The structure consists of both isolated and face-shared WO6 octahedra and, surprisingly, isolated WO6 trigonal prisms. A careful analysis of the packing arrangement in the structure makes it possible to explain the unusual structural architecture of Ce18W10O57, which is described in detail. The temperature-dependent magnetic susceptibility of Ce18W10O57 indicates that the cerium(III) f1 cations do not order magnetically and exhibit simple paramagnetic behavior. The SHG efficiency of Ln18W10O57 (Ln = La, Ce) was measured as a function of particle size, and both compounds were found to be SHG active with efficiency approximately equal to that of α-SiO2.

Salt-inclusion compounds (SICs) are known for their structural diversity and their potential applications, including luminescence and radioactive waste storage forms. Currently, the majority of salt-inclusion phases are grown serendipitously and the targeted growth of SICs has met with only moderate success. We report an enhanced flux growth method for the targeted growth of SICs. Specifically, the use of (1) metal halide reagents and (2) reactions with small surface area to volume ratios are found to favor the growth of salt-inclusion compounds over pure oxides and thus enable a more targeted synthetic route for their preparation. The Cs–X–U–Si–O (X = F, Cl) pentanary phase space is used as a model system to demonstrate the generality of this enhanced flux method approach. Single crystals of four new salt-inclusion uranyl silicates, [Cs3F][(UO2)(Si4O10)], [Cs2Cs5F][(UO2)2(Si6O17)], [Cs9Cs6Cl][(UO2)7(Si6O17)2(Si4O12)], and [Cs2Cs5F][(UO2)3(Si2O7)2], were grown using this enhanced flux growth method. A detailed discussion of the factors that favor salt-inclusion phases during synthesis and why specifically uranyl silicates make excellent frameworks for salt-inclusion phases is given.

A family of lanthanide mixed-valent vanadium(III/IV) oxosilicates Ln4V5–xZnxSi4O22 (Ln = La, Ce, Pr, and Nd) was synthesized as high-quality single crystals via a high-temperature molten salt method. An in situ reduction of V(V) to V(III/IV) as well as of Ce(IV) to Ce(III) was achieved utilizing Zn metal as the reducing agent, some of which is incorporated into the crystal structure. Ce4V4.77Zn0.23Si4O22, to the best of our knowledge, is the first example of a cerium-containing mixed-valent vanadium silicate. The crystal structures were determined by single-crystal X-ray diffraction, and the four isostructural oxosilicates were determined to crystallize in the chevkinite-structure type in the monoclinic space group I2/a. The unit cells of the Ln4V5–xZnxSi4O22 (Ln = La, Ce, Pr, and Nd) series are related to the reported C2/m phases Ln4V5Si4O22 (Ln = La, Pr, and Nd) by a doubling of the c-axis and a loss of a mirror plane. The three-dimensional crystal structure consist of two-dimensional rutile-based vanadium oxide and lanthanide oxide layers linked via Si2O7 groups. The temperature dependence of the magnetic susceptibility of these compounds was measured, and only the Nd analogue exhibited a magnetic transition at 5 K; all samples displayed a discontinuity or deviation from linearity at ca. 130–150 K.

Single crystals of K8(K5F)U6Si8O40 were grown from a mixed alkali halide flux. K8(K5F)U6Si8O40 is the first intergrowth uranyl silicate, being composed of alternating slabs related to two previously reported uranyl silicates: Cs2USiO6 and [Na9F2][(UO2)(UO2)2(Si2O7)2]. It exhibits intense luminescence, which is influenced by the [(UO2)2O] dimers present in the structure.

A series of six anti-perovskite fluorides of the type [Cu(H2O)4]3(M1–xM′xF6)2 (where M and M′ = V, Cr, Mn, Fe as well as M = Fe and M′ = V and Cr) was synthesized as high-quality single crystals via a mild hydrothermal route. These materials belong to a class of perovskite-based structures in which the anions and cations of the regular ABX3 perovskite structure have exchanged positions. Two complex anions, MF63– and M′F63–, occupy the normal A and B cation positions, while three complex cations, [Cu(H2O)4]2+, occupy the normally anionic X positions. As in the ABX3 compositions, the A and B positions can be occupied by different complex anions, allowing for the preparation of a wide range of compositions. Magnetic property measurements were performed on all six phases, and complex magnetic behavior was observed at low temperatures in the Mn, Fe, and bimetallic Fe/V and Fe/Cr phases.

Four new reduced lanthanide molybdenum oxides containing mixed valent Mo(V/VI)O4 tetrahedra were prepared in single crystal form by utilizing a high temperature molten salt flux synthesis involving an in situ reduction step. Calculations support the experimentally observed result that large alkali metal cations such as cesium are superior compared to the smaller alkali metal cations such as sodium in solvating O2– to facilitate oxide crystal growth in halide melts. All four compounds were structurally characterized by single crystal and powder X-ray diffraction methods and were found to crystallize in the cubic space group Pn3̅n. The temperature dependence of the magnetic susceptibility of these compounds was measured, and all were found to exhibit simple paramagnetism.

Two polymorphs of K3YSi2O7, crystallizing in the space groups P63/mmc (1) and P63/mcm (2) can be synthesized by high temperature flux crystal growth. The flux growth conditions can be fine-tuned to yield a phase pure sample of polymorph (2), however, not of polymorph (1), which always co-crystallizes with polymorph (2). Polymorph (2) was found to exhibit intrinsic bluish-white light emission. Further studies determined that doping europium and dysprosium onto the yttrium site of this polymorph could readily tune the luminescence, with the purest white light emission found for the K3YSi2O7: 10% Dy, 0.1% Eu composition (K3Y0.899Dy0.1Eu0.001Si2O7) (2-Dy,Eu).

Single crystals of two new salt-inclusion uranium(VI) silicates, [NaK6F][(UO2)3(Si2O7)2] and [KK6Cl][(UO2)3(Si2O7)2], were grown from mixed alkali halide salt fluxes. Both compounds crystallize in the [NaRb6F][(UO2)3(Si2O7)2] structure type in the orthorhombic space group Pnnm with lattice parameters a = 11.0819(5) Å, b = 13.1149(6) Å, and c = 7.8418(4) Å ([NaK6F]) and a = 11.0830(7) Å, b = 13.5850(4) Å, and c = 7.8693(5) Å ([KK6Cl]). The surface area to volume (sa/vol) ratio of the reaction, controlled by the reaction vessel dimensions, has a strong influence on the reaction products with small sa/vol ratios favoring the growth of the salt-inclusion phases. Both compounds exhibit the typical luminescence of the uranyl group with the luminescence of [KK6Cl][(UO2)3(Si2O7)2] being less intense than [NaK6F][(UO2)3(Si2O7)2], likely due to quenching by the Cl– ions.

A series of monoclinic distorted double perovskites of the general formula Ln2MIrO6 (Ln = La, Pr, Nd, Sm–Gd; M = Mg, Ni) were grown as highly faceted single crystals from a potassium hydroxide flux. The structural distortions and the magnetic interactions in A2BB′O6 double perovskites can be “designed” via a judicious choice of A, B, and B′ cation sizes and by selecting magnetic or nonmagnetic ions to occupy the A, B, and/or B′ sites. A study of the relationship between the number of magnetic ions, the degree of monoclinic distortion, and the resulting magnetic interactions was conducted. Magnetic susceptibility and field dependent magnetization measurements were performed for all synthesized compounds. It was determined that smaller A-site lanthanide cations cause more pronounced monoclinic distortions, resulting in smaller M–O–Ir (M = Mg, Ni) bond angles that correlate with higher magnetic ordering temperatures. The magnetic susceptibility and field dependent magnetization data were both consistent with canted antiferromagnetism for most titled compositions, indicating a possible trend of increased spin canting, and thus increased ferromagnetic-like interactions, as a function of smaller lanthanide A site cation size.

•Na2RESiO4(OH) (RE = Yb, Sc) have been synthesized by the hydroflux method.•NaRESiO4 (RE = La, Yb) have been synthesized by fluoride flux growth.•Size effects of rare earth silicates are presented.Crystals of Na2ScSiO4(OH) and Na2YbSiO4(OH) were synthesized at low temperatures using a sodium hydroxide based hydroflux, while crystals of NaLaSiO4 and NaYbSiO4 were grown at high temperatures using a sodium fluoride/sodium chloride eutectic flux. Both structure types were crystallized under reaction conditions that, when used for medium sized rare earths (RE = Pr, Nd, Sm – Tm) yield the Na5RE4X[SiO4]4 structure type, where X is OH in the hydroflux conditions and F in the eutectic flux conditions. Herein, we report the synthesis, structure, size effect, and magnetic properties of these compositions and introduce the new structure type of Na2RESiO4(OH), which crystallizes in the orthorhombic space group Pca21, of NaLaSiO4, which crystallizes in the orthorhombic space group Pna21, and of NaYbSiO4, which crystallizes in the orthorhombic space group Pnma, where both NaRESiO4 compounds have one silicon structural analog.

Five new lanthanide molybdenum oxides containing mixed valent Mo(IV/V) rutile-like chains, Ln5Mo2O12 Ln = Eu, Tb, Dy, Ho, and Er, were prepared utilizing a high-temperature molten salt flux synthesis involving an in situ reduction utilizing metallic reducing agents. All five compounds were structurally characterized by single-crystal and powder X-ray diffraction methods and were found to crystallize in the monoclinic space group C2/m. The molybdates all contain rare infinite chains consisting of MoO2O4/2 edge-sharing octahedra. The chains exhibit alternating long and short separations between octahedra caused by the presence of Mo–Mo bonds to form Mo2O10 units containing one unpaired electron. The temperature dependence of the magnetic susceptibility of these compounds was measured, and antiferromagnetic ordering was observed in all cases.

Single crystals of three new alkali-metal manganese uranium oxides, K2MnU3O11, Rb2MnU3O11, and Li3.2Mn1.8U6O22, have been grown from molten chloride fluxes and structurally characterized by single-crystal X-ray diffraction. The first two compounds crystallize in the trigonal space group, R3̅c, in the three-dimensional (3D), natrotantite structure composed of α-U3O8-topological layers connected via MnO6 octahedra. The Li-containing compound crystallizes in the monoclinic space group, Cc, with a related 3D structure, composed of β-U3O8-topological sheets connected via irregular MnO7 polyhedra. All three compounds exhibit typical uranyl, UO22+, coordination environments consisting of either UO7 pentagonal bipyramids or UO6 flattened octahedra. The lattice parameters of the new oxides are K2MnU3O11, a = 6.8280(2) Å, c = 36.8354(17) Å; Rb2MnU3O11, a = 6.8407(2) Å, c = 37.5520(17) Å; and Li3.2Mn1.8U6O22, a = 11.8958(8) Å, b = 10.9639(7) Å, c = 13.3269(8) Å, and β = 91.442(4)°. The magnetic susceptibilities of the K and Rb phases are discussed.

Single crystals of NaEu9(SiO4)6O2, Na1.5Eu8.5(SiO4)6OF, Na1.64Gd8.36(SiO4)6O0.72F1.28, Gd9.34(SiO4)6O2, Ca2.6Eu7.4(SiO4)6O1.4F0.6, Ca4.02Sm5.98(SiO4)6F2, and K1.32Pr8.68(SiO4)6O1.36F0.64 and powders of NaEu9(SiO4)6O2, Na1.5Eu8.5(SiO4)6OF, Eu9.34(SiO4)6O2, and Gd9.34(SiO4)6O2 were synthesized via flux growth in selected alkali-fluoride melts. All of the compounds adopt the apatite structure with space group P63/m. Luminescence and magnetic data were collected on NaEu9(SiO4)6O2, Na1.5Eu8.5(SiO4)6OF, Eu9.34(SiO4)6O2, and Gd9.34(SiO4)6O2. Luminescent data indicate that changing the cations and anions that surround the lanthanide site does not change the luminescent properties, making apatites versatile structures for optical materials.

A series of new, complex U(IV) fluorides, namely, Na3MU6F30 (M = Al3+, Ga3+, Ti3+, V3+, Cr3+, and Fe3+), containing trivalent transition- and main-group metal cations were synthesized via an in situ reduction step of U(VI) to U(IV). Single crystals of the series were grown in high yield under mild hydrothermal conditions and were characterized by single-crystal X-ray diffraction. The reported compounds crystallize in the trigonal space group P3̅c1 and exhibit complex crystal structures with a three-dimensional (3-D) framework composed of corner- and edge-shared UF9 polyhedra. The arrangement of U2F16 dimers forms two types of hexagonal channels, where MF6 polyhedra and sodium atoms are located. The most interesting structural feature is the presence of the 3-D framework that can accommodate various transition-metal ions in low oxidation states, indicating that the framework acts as an excellent host. Trivalent transition metal ions, even reduced Ti3+ and V3+, were stabilized by both the rigid framework and by our synthetic conditions. Utilizing ionic radii of transition metal ions, a phase boundary was investigated, suggesting that there exists a size limit for the M site in the crystal structure. The valence state of uranium was studied by U 4f X-ray photoelectron spectroscopy, which confirmed the presence of U4+. Temperature-dependent magnetic susceptibility measurements yielded effective magnetic moments of 3.50 and 3.35 μB for Na3MU6F30 (M = Al3+ and Ga3+), respectively. For the other compounds, combined effective magnetic moments of 8.93, 9.09, 9.18, and 10.39 μB were obtained for Ti, V, Cr, and Fe members, respectively. In all cases, large negative Weiss constants were observed, which are indicative of the existence of a spin gap in U4+. Field-dependent magnetic property measurements at 2 K for Na3FeU6F30 demonstrated that U4+ attains a nonmagnetic singlet ground state at low temperature. Optical and thermal properties were measured and are reported.

Four new oxovanadium(IV) tartrates, namely, A2[(VO)2(C4H4O6)(C4H2O6)(H2O)2]·(H2O)2, where A = Cs, 1, Rb, 2; K2[(VO)2(C4H2O6)2(H2O)2]·(H2O)2, 3; and Na2[(VO)2(C4H4O6)(C4H2O6)(H2O)7]·(H2O)2, 4, were prepared utilizing a two-step, mild hydrothermal route involving l-(+)-tartaric acid as the reducing agent. All four compounds were structurally characterized by single-crystal and powder X-ray diffraction methods and were found to crystallize in the non-centrosymmetric orthorhombic space groups P212121 for 1, 2, and 4 and C2221 for 3. The temperature dependence of the magnetic susceptibility of these compounds was measured, and 1, 2, and 4 were found to be paramagnetic down to 2 K, while 3 was found to exhibit spin-dimer behavior. Compounds 1, 2, and 3 were found to be second harmonic generation active. All compounds were further characterized by IR and UV–vis spectroscopies.

Single crystals of two uranium silicates, Cs2USiO6 and Rb2USiO6, have been grown from molten fluoride fluxes and structurally characterized by single-crystal X-ray diffraction. Cs2USiO6 crystallizes in the body-centered orthorhombic space group, Immm, with a = 8.5812(4) Å, b = 13.0011(6) Å, and c = 13.8811(7) Å. The size of Rb is slightly too small to fit into this structural framework without effecting slight structural changes that result in a 6-fold superstructure. Sharp satellite peaks were observed in the single-crystal X-ray diffraction data, indicating the existing of a superstructure. The crystals were examined by electron diffraction, the results of which suggest that the structure can be thought of as the Immm isotype (a = 8.4916(6) Å, b = 12.6678(9) Å, and c = 13.5077(9) Å) on average, with an approximately 6-fold superstructure along the c axis. The materials were further characterized by UV–vis reflectance spectroscopy.

The flux growth of uranium(IV) oxides presents several challenges, and to the best of our knowledge, only one example has ever been reported. We succeeded in growing two new reduced uranium silicates A2USi6O15 (A = K, Rb) under flux growth conditions in sealed copper tubes. The compounds crystallize in a new structure type with space group C2/c and lattice parameters a = 24.2554(8) Å, b = 7.0916(2) Å, c = 17.0588(6) Å, β = 97.0860(6) ° (K) and a = 24.3902(8) Å, b = 7.1650(2) Å, c = 17.2715(6) Å, β = 96.8600(6) ° (Rb). A2USi6O15 (A = K, Rb) are isocompositional to a previously reported Cs2USi6O15, and the two structures are compared. K2USi6O15 undergoes an interesting crystal-to-crystal structural phase transition at T ≈ 225 K to a triclinic structure, which is accompanied by an intense color change. The magnetic properties of A2USi6O15 (A = K, Rb, Cs) are reported and differ from the magnetism observed in other U4+ compounds. Calculations are performed on the (UO6)−8 clusters of K2USi6O15 to study the cause of these unique magnetic properties.

A layered quaternary uranium-containing oxide, Cs2Mn3U6O22, was crystallized from a cesium chloride flux. The crystal structure was determined to consist of α-U3O8 topological layers that are separated by alternating cesium and manganese layers. This ordered arrangement creates a separation between manganese layers of 13 Å, leading to complex low-dimensional magnetic properties. The compound crystallizes in a new structure type in the monoclinic space group, C2/m, with a = 6.8730(10) Å, b = 11.7717(17) Å, c = 13.374(2) Å, and β = 99.673(5)°. The magnetic properties were measured and analyzed by first-principles density functional theory calculations.

•Phenylphosphonate (PPA) readily grafts onto calcium niobate (CN) platelets.•Demonstrates covalent grafting onto face surfaces of an exfoliated layered perovskite.•Demonstrates organophosphonic acid grafting onto a layered niobate in water.•Explores role of CN dispersion state and solvent on amount and mode of PPA grafting.•Proposed grafting mechanism rationalizes primarily bidentate grafting of PPA on CN.HypothesisThis work explores covalent grafting of phenylphosphonate (PPA) onto exfoliated, protonated calcium niobate (HCN), a Dion-Jacobson layered perovskite. The specific hypothesis is that PPA can be readily grafted onto the face surfaces of exfoliated HCN, which has reactive apical oxygen atoms.ExperimentsPrevious research has established the conditions required for full exfoliation of HCN in aqueous solutions of tetrabutylammonium hydroxide (TBAOH), denoted as TBACN. This work first explores the effect of reflux conditions on the dispersion state of TBACN suspensions, and then investigates PPA grafting onto both non-exfoliated HCN and exfoliated TBACN dispersed in deionized (DI) water, TBA solution, and various alcohols. The products are characterized by a variety of techniques including light scattering to assess the TBACN dispersion state, 31P MAS NMR to confirm PPA grafting, and XPS to estimate PPA grafted amounts.FindingsThe results confirm the grafting of PPA on HCN and TBACN, quantify the extent of PPA grafting, and identify various grafting modes (mono-, bi-, and tridentate). All of these aspects are found to be dependent on the layered materials’ exfoliation state, suspension processing conditions, and solvent composition. The results are rationalized in terms of a plausible mechanism of the grafting process.

Single crystals of Na5RE4(OH)[SiO4]4 (RE = Pr, Nd, Sm, Eu, Tb–Yb, Y) were grown using the hydroflux synthetic method. All compositions adopt the tetragonal I space group with lattice parameter ranges of a = 11.5275(4)–12.0588(3) Å and c = 5.3951(4)–5.4846(13) Å. Intense photoluminescent properties were observed for Na5Eu4(OH)[SiO4]4, Na5Gd4(OH)[SiO4]4, and Na5Tb4(OH)[SiO4]4. The magnetic susceptibility was measured for the magnetic rare earth containing compositions, where the terbium analogue displayed antiferromagnetic order at T = 2.8 K.

Crystals of Na5RE4F[SiO4]4 (RE = Pr, Nd, Sm–Tm) and K5Pr4F[SiO4]4 were grown using a fluoride flux synthetic technique. All compositions crystallize in the tetragonal space group I with lattice parameter ranges of a = 11.5094(2)–12.3745(2) Å and c = 5.37000(10)–5.5011(2) Å. Antiferromagnetic ordering is observed for Na5RE4F[SiO4]4 (RE = Tb, Dy), second harmonic generation for Na5RE4F[SiO4]4 (RE = Pr, Sm–Ho), and intense optical properties and fluorescence quantum yield for Na5RE4F[SiO4]4 (RE = Eu, Gd, Tb). The crystal structures and physical property measurements are discussed.

Single crystals of Cs2.2U5O16 and Cs2U4O13 have been synthesized from a CsCl flux with the ramp rate controlling the formation of fully oxidized Cs2U4O13versus partially reduced Cs2.2U5O16. Their structures have been determined by single crystal X-ray diffraction. Cs2.2U5O16 crystallizes in the monoclinic space group C2/m with lattice parameters a = 13.4160(5) Å, b = 15.5089(6) Å, c = 7.9723(3) Å, and β = 92.7120(10)° and Cs2U4O13 crystallizes in the orthorhombic space group Ccmm with lattice parameters a = 13.5031(6) Å, b = 15.4048(7) Å, c = 39.5680(17) Å. The two compounds contain related uranium frameworks with disordered Cs atoms within the channels. Both structures contain multiple cation–cation interactions, CCIs, which arise due to the three dimensional nature of the framework. Magnetic properties are reported for Cs2.2U5O16, which contains mixed valent U.

Single crystals of K4CaUSi4O14 have been grown from a eutectic CaF2–KF flux. K4CaUSi4O14 crystallizes in a new structure which exhibits a 49-fold superstructure believed to be due to a modulation of the uranium and silicon polyhedra. We report the sub-cell of the structure which adopts the tetragonal space group Pn2 with lattice parameters a = 9.2862(2) Å, c = 8.3796(4) Å, and V = 722.60(5) Å3. K4CaUSi4O14 is a member of a structural family related to the mineral fresnoite which we describe here. Finally, we report UV-vis absorbance and SHG measurements on the compound, which is non-centrosymmetric.

•Na5Ln(OH)6WO4 (Ln = Er, Tm, Yb) have been synthesized and characterized.•Crystals were grown in a hydroflux.•Low temperature synthetic route to synthesize oxyhydroxides is presented.Single crystals of Na5Ln(OH)6WO4 where Ln = Er, Tm, and Yb were grown out of a NaOH hydroflux. The crystals were characterized by single crystal X-ray diffraction and were found to crystallize in the monoclinic space group I2/a. The lattice parameter ranges for the three structures are a = 11.2024(7) Å–11.2412(6) Å, b = 16.1850(10) Å–16.2220(10) Å, and c = 11.9913(7) Å–12.0323(7) Å while the β angle range is 101.999(2)°–102.025(2)°.

•Transformation from peroxide, hydrate, and fluoride precursors to anhydrous K2TiOF4 are unlikely to succeed.•Direct synthesis of K2TiOF4 was employed to grow single crystals.•Crystals were characterized by single crystal x-ray diffraction.The synthesis of anhydrous K2TiOF4 has been previously attempted by transforming precursor compounds, such as the peroxide (K2Ti(O2)F4), hydrate (K2TiOF4·H2O) and fluoride (K2TiF6). Due to the large structural differences between these precursors and the anhydrous oxyfluorides, however, these preparations have been unsuccessful. Therefore, a direct method of synthesis has been employed to grow single crystals of K2TiOF4 that were characterized by single crystal x-ray diffraction. K2TiOF4 was found to be isostructural with the previously known K2VOF4.Synthesis of anhydrous K2TiOF4 has been previously attempted by transforming precursor compounds such as the peroxide (K2Ti(O2)F4), hydrate (K2TiOF4·H2O) and fluoride (K2TiF6). Due to the large structural differences between these precursors and the anhydrous oxyfluorides, these preparations have been unsuccessful. Therefore, a direct method of synthesis has been employed to grow single crystals of K2TiOF4 that were characterized by single crystal X-ray diffraction.

Single crystals of K5Y2FSi4O13 were grown out of a molten potassium fluoride flux. Single crystal X-ray diffraction was used to determine the crystal structure. K5Y2FSi4O13 crystallizes in the monoclinic space group P21/m with a = 7.1567(12) Å, b = 5.7627(9) Å, c = 18.005(3) Å, β = 92.396(4)°, and Z = 2. This compound has a complex three-dimensional structure with corner-sharing YO5F and SiO4 polyhedra.

Single crystals of Na4(AsO4)OH were grown using the hydroflux method and characterized by single crystal X-ray diffraction. Na4(AsO4)OH crystallizes in the orthorhombic space group Pnma with a = 8.9467(11) Å, b = 7.3854(9) Å, and c = 8.2395(10) Å. The moisture sensitive material exhibits a three-dimensional crystal structure consisting of isolated AsO43− tetrahedra with the charge balance maintained by Na+ and OH−. The asymmetric unit consists of one arsenic atom, three sodium atoms, four oxygen atoms, and one hydroxyl hydrogen atom. Arsenic, sodium, and oxygen atoms, as well as the hydroxyl hydrogen, are located on mirror planes; sodium is located on an inversion center.

A molten potassium fluoride flux was used to grow single crystals of K5Sc2FSi4O13. The crystals were characterized by single crystal X-ray diffraction. K5Sc2FSi4O13 crystallizes in the monoclinic space group P21/m with lattice parameters of a = 6.9681(14) Å, b = 5.5830(11) Å, and c = 17.829(4) Å and a β angle of 91.52(3)°. This compound has a complex three-dimensional structure.

A family of rare U(IV)-containing quaternary fluorides, Na4MU6F30 (M = Mn2+, Co2+, Ni2+, Cu2+, and Zn2+), was synthesized in single crystal form via a mild hydrothermal technique utilizing an in situ U(VI) to U(IV) reduction step. The modified hydrothermal route is described, and the conditions to obtain single crystals in high yield are detailed. The crystal structures were determined by single crystal X-ray diffraction. The isostructural fluorides crystallize in a new structure type in the trigonal space group P3̅c1. They exhibit a complex three-dimensional crystal structure consisting of corner- and edge-shared UF9 and MF6 polyhedra. The main building block, a U6F306– group, is arranged to create two distinct hexagonal channels, inside which MF6 octahedra and Na+ cations are located. The copper-containing member of the series, Na4CuU6F30, is unusual in that the Cu2+ cation exhibits a rare symmetrical coordination environment consisting of six identical Cu–F bond distances, indicating the lack of the expected Jahn–Teller distortion. Magnetic susceptibility measurements of Na4ZnU6F30 yielded an effective magnetic moment of 3.42 μB for the U4+ (f2) cation in the structure. Measurements of the other members containing magnetic transition-metal cations in addition to U4+, Na4MU6F30 (M = Mn2+, Co2+, Ni2+, and Cu2+) yielded total effective magnetic moments of 10.2, 9.84, 8.87, and 8.52 μB for the Mn-, Co-, Ni-, and Cu-containing materials, respectively. No evidence for long-range magnetic ordering was found down to 2 K. Measurements of the magnetization as a function of applied magnetic field at 2 K for Na4MnU6F30 confirmed that the U4+ magnetic cation exhibits a nonmagnetic singlet ground state at low temperature. Thermal stability measurements and UV–vis diffuse reflectance spectroscopy are also reported.

Crystallographic structural changes were investigated for Sr2Fe1.5Mo0.5O6−δ, an electrode material for symmetric solid oxide fuel cells. The samples of this material were heated and cooled in wet hydrogen and wet oxygen atmospheres, to simulate the reducing and oxidizing conditions experienced under actual fuel cell operating conditions, and their structures and oxygen contents were determined using in situ powder neutron diffraction. The existence of a reversible tetragonal to cubic phase transition was established to occur between room temperature and 400 °C, both on heating and cooling in either oxygen or hydrogen. The oxygen content reaches a low value of 5.50(2) at 850 °C in wet hydrogen. Excellent correlations are observed between the oxygen content of the structure and the conductivities reported in the literature.

Single crystals of several ternary alkali uranium fluorides, LiUF5, KU2F9, K7U6F31, RbUF5, RbU2F9, and RbU3F13, have been obtained in a mild hydrothermal process using UO2(CH3CO2)2(H2O)2 as the uranium source. Their crystal structures were determined by single crystal X-ray diffraction. The uranium in the starting reagent was successfully reduced from U6+ to U4+ in a dilute hydrofluoric acid environment, aided by the presence of a copper salt. All materials exhibit highly complex crystal structures that range from two-dimensional to three-dimensional. The U4+ cations are found in high (UF8 and UF9) coordination environments. The magnetic susceptibility measurements yielded effective magnetic moments of 3.01–3.83 μB for the U4+ cations. The temperature dependent magnetic susceptibility measurements confirmed that the U4+ cation exhibits a nonmagnetic singlet ground state at low temperatures. No long-range magnetic order was observed for any of the above compositions down to 2 K. Optical and thermal behaviors of the fluorides were also investigated.

A new reduced vanadium oxalate, Ba3[(VO)2(C2O4)5(H2O)6]·(H2O)3, 1, was synthesized via a two-step, mild hydrothermal method using oxalic acid as the reducing agent. This compound undergoes multiple single-crystal to single-crystal phase transitions as a function of water content to form Ba3[(VO)2(C2O4)5(H2O)4]·(H2O)2, 2, and Ba3[(VO)2(C2O4)5(H2O)2], 3, after heating 1 to 50 and 100 °C, respectively. In addition, exposing 1 to a vacuum for 12 h also transforms it into 2, but not 3. All three compositional variants were structurally characterized by single crystal X-ray diffraction and are found to crystallize in the monoclinic space groups of C2/c and P21/c, for 1 and 2, and 3, respectively. Vanadium in these structures retains the +4 oxidation state, indicating exceptional crystal stability. The magnetic susceptibility of these compounds was measured, and all three materials were found to be paramagnetic down to 2 K. Compound 1 was further characterized by IR, UV-vis spectroscopy, and thermal analysis.

Single crystals of five new alkali metal uranium oxychlorides, K4U5O16Cl2, Rb4U5O16Cl2, Cs5U7O22Cl3, RbUO3Cl, and CsUO3Cl, have been grown from molten chloride fluxes and structurally characterized by single crystal X-ray diffraction. All of the materials are monoclinic. The first three crystallize in the space group P21/n and exhibit a 2D layered structure with a novel layer topology, consisting of UO6, UO7, and UO4Cl2 polyhedra and cation–cation interactions (CCIs) within the plane of the uranyl sheet. A general cation–cation classification scheme is presented. RbUO3Cl and CsUO3Cl crystallize in the space group P21/m and exhibit 1D zipper-like chains of UO5Cl2 polyhedra. The lattice parameters of the new oxychlorides are: K4U5O16Cl2, a = 9.9574(4) Å, b = 6.9766(3) Å, c = 14.3920(6) Å, and β = 105.7690(10)°; Rb4U5O16Cl2, a = 10.2164(4) Å, b = 7.0160(3) Å, c = 14.4930(5) Å, and β = 103.8290(10)°; Cs5U7O22Cl3, a = 10.6214(5) Å, b = 18.1071(8) Å, c = 16.0857(7) Å, and β = 102.9850(10)°; RbUO3Cl, a = 7.3602(6) Å, b = 4.1127(3) Å, c = 8.5556(7) Å, and β = 104.602(2)°; CsUO3Cl, a = 7.7768(4) Å, b = 4.1245(2) Å, c = 8.7701(5) Å, and β = 105.4680(10)°. The materials were further characterized by UV-vis reflectance spectroscopy and fluorescence spectroscopy.

•NaLnGeO4 (Ln = Sm, Eu, Gd, Tb) have been synthesized and characterized.•The oxides exhibit a complex three-dimensional crystal structure.•Magnetic susceptibility data were collected.•The room temperature photoluminescence was investigated.Single crystals of NaLnGeO4 (Ln = Sm, Eu, Gd) were grown out of a molten sodium hydroxide flux, and their crystal structures were determined by single crystal X-ray diffraction. The lanthanide containing germanates crystallize in the orthorhombic space group of Pnma, and exhibit a complex three-dimensional structure consisting of corner- or edge-shared LnO6, GeO4, and NaO6 polyhedra. UV–vis diffuse reflectance spectra indicated that the reported oxides are insulating materials with wide band gaps. The magnetic susceptibility data shows paramagnetic behavior. For the NaEuGeO4 and NaTbGeO4 compositions intense room temperature photoluminescence was observed.Single crystals and powder samples of NaLnGeO4 (Ln = Sm, Eu, Gd, Tb) were prepared via a sodium hydroxide melt and conventional solid-state methods. The three-dimensional crystal structure was determined by single crystal X-ray diffraction. Magnetic susceptibility data were collected and the room temperature photoluminescence was investigated.

•Single crystal growth of K2Ba(CrO4)2, K2Ba(MoO4)2, K2Ba(WO4)2 using a hydroxide hydroflux.•Anti-site mixing between potassium and barium correlates with the group 6 metal radius.•Diffuse reflectance and luminescence measured.Single crystals of a family of quaternary oxides K2Ba(MO4)2 (M = Cr, Mo, W) have been grown for the first time. The crystals were grown in a hydroxide-based hydroflux. The compounds crystallize in space group R  3¯m and, according to single-crystal X-ray diffraction structure determination, are isostructural with the mineral Palmierite. All compounds show anti-site mixing of the potassium and barium. The degree of mixing appears to be determined indirectly by the M-O bond distance. Diffuse reflectance spectra and room-temperature luminescence were measured for each compound.

•KBaAsO4 and KBaMnO4 crystals were grown using the hydroflux method.•Crystals of a rare Mn5+ oxide were obtained.•The crystals were characterized by single crystal X-ray diffraction.•The magnetic properties of the crystals were studied.Single crystals of KBaMnO4 and KBaAsO4 were grown using the hydroflux method and characterized by single crystal X-ray diffraction. Both compounds crystallize in the orthorhombic space group Pnma with a = 7.7795(4) Å, b = 5.8263(3) Å, and c = 10.2851(5) Å for the manganate and a = 7.7773(10) Å, b = 5.8891(8) Å, and c = 10.3104(13) Å for the arsenate. The materials exhibit a three-dimensional crystal structure consisting of isolated MnO43− or AsO43− tetrahedra, with the charge balance maintained by K+ and Ba2+. Each tetrahedron is surrounded by six K+ and five Ba2+, and shares its corner/edge with KO10 polyhedra and corner/edge/face with BaO9 polyhedra, respectively. The crystal growth, crystal structure and magnetic properties are discussed.

•Synthesis of MnUO4, MnUO4, and NiU2O6 single crystals reported.•KCl, CsCl, and BaCl2 employed for flux crystal growth.•Pentavalent uranium complex oxides presented.•Single crystal structures discussed.Single crystals of MnUO4, FeUO4, and NiU2O6 were grown for the first time. The use of chloride fluxes facilitated the crystal growth. MnUO4, a hexavalent uranium compound, crystallizes in the orthorhombic space group, Imma, with a = 6.6421(19) Å, b = 6.978(2) Å, and c = 6.748(2) Å, and exhibits typical uranyl, UO22+, coordination. FeUO4 and NiU2O6 contain pentavalent uranium and are structurally related, exhibiting three-dimensional connectivity. FeUO4 crystallizes in the orthorhombic space group, Pbcn, with a = 4.8844(2) Å, b = 11.9328(5) Å, c = 5.1070(2) Å. NiU2O6 crystallizes in the trigonal space group, P321, with a = 9.0148(3) Å, c = 5.0144(3) Å.

•Three Nd containing silicates have been synthesized and characterized.•Na0.50Nd4.50(SiO4)3O, Na0.63Nd4.37(SiO4)3O0.74F0.26 are apatite structures.•Eutectic flux crystal growth was used to synthesize these new silicate structures.Single crystals of Na0.50Nd4.50(SiO4)3O, Na0.63Nd4.37(SiO4)3O0.74F0.26, and Na4.74Nd4.26(O0.52F0.48)[SiO4]4 were synthesized via flux growth using a NaF/KF eutectic flux and the crystal structure was determined by single crystal X-ray diffraction. Na0.50Nd4.50(SiO4)3O and Na0.63Nd4.37(SiO4)3O0.74F0.26 adopt the apatite structure and crystallize in the hexagonal space group P63/m, while Na4.74Nd4.26(O0.52F0.48)[SiO4]4 crystallizes in the tetragonal space group I-4 and exhibits rare-earth mixing on the sodium site. The unit cells of the crystals are a = 9.5400(3) Å and c = 7.0331(5) Å for Na0.50Nd4.50(SiO4)3O, a = 9.5533(3) Å and c = 7.0510(4) Å for Na0.63Nd4.37(SiO4)3O0.74F0.26, and a = 12.1255(3) Å and c = 5.4656(2) Å for Na4.74Nd4.26(O0.52F0.48)[SiO4]4. These three compounds exhibit three-dimensional crystal structures that are discussed in detail in this paper.

Single crystals of K8U7O24 (K8U7.04O24) were grown out of a reactive potassium fluoride flux and characterized by single crystal X-ray diffraction. The reaction was carried out in a sealed copper tube. The title compound crystallizes in the cubic space group Im-3m with a = 8.65050(10) Å. The material exhibits an ordered perovskite structure type that is a 2 × 2 × 2 cubic superstructure of the CaTiO3 perovskite type. Six of the uranium atoms in the composition are in the +6 oxidation state, while the seventh one is +4. The uranium(VI) atom is located in a distorted UO6 octahedral coordination environment containing two short, 1.966(5) Å, and four long, 2.16260(10) Å, U–O bonds, consistent with the uranyl cation, UO22+. The uranium(IV) atom is in a regular octahedral environment with U–O bonds of 2.359(5) Å.

Single crystals of the tungsten (VI) oxide hydrate, Ba2WO5·H2O, were grown using a hydroxide hydroflux. The structure was determined by single crystal X-ray diffraction. Ba2WO5·H2O crystallizes in the space group P21/n with a = 7.6710(15) Å, b = 9.8538(20) Å, c = 8.5520(17) Å, and β = 111.838(30)°. The crystal structure is comprised of [W2O10]8− dimeric units that are connected to surrounding barium cations located in face-, edge-, and corner-shared 8- and 9-fold coordination environments; the water of crystallization is only bound to barium.

A series of new mixed-metal oxalates containing U4+ and divalent transition metal cations, Na2U2M(C2O4)6(H2O)4 (M = Mn2+, Fe2+, Co2+, and Zn2+), were synthesized via a hydrothermal route and structurally characterized by single crystal X-ray diffraction. All of the materials are triclinic, with space group P1̅. The three-dimensional structure of these isostructural uranates consists of oxalate bridged UO10 and MO6 polyhedra. The U4+ cation is surrounded by five oxalate ligands, while the M2+ cations are bonded to two oxalate ligands and four water molecules. The magnetic susceptibility data of these mixed metal oxalates were measured as a function of temperature and result in a value of the effective magnetic moment of 3.50 μB for U4+ cation in the Zn member, while the total effective moment of the Mn2+, Fe2+, and Co2+ members are 6.01, 5.46, and 5.06 μB, respectively. For all materials, negative Weiss constants were observed revealing that the materials exhibited local antiferromagnetic interactions. The U4+ cation exhibits a singlet ground state at low temperature. The materials were further characterized by infrared, UV–vis reflectance spectroscopy, and thermal analysis.

Cesium vanadate, Cs2V3O8, a member of the fresnoite-type structure, was synthesized via a hydrothermal route and structurally characterized by single-crystal X-ray diffraction. Cs2V3O8 crystallizes in a noncentrosymmetric polar space group, P4bm, with crystal data of a = 8.9448(4) Å, c = 6.0032(3) Å, V = 480.31(4) Å3, and Z = 2. The material exhibits a two-dimensional layered crystal structure consisting of corner-shared V5+O4 and V4+O5 polyhedra. The layers are separated by the cesium cations. The alignment of the individual polyhedra results in a macroscopic polarity for Cs2V3O8. Frequency-dependent polarization measurements indicate that the material is not ferroelectric. A pyroelectric coefficient of −2.0 μC m–2 K–1 was obtained from pyroelectric measurements taken as a function of the temperature. The magnetic susceptibility data were measured as a function of the temperature and yielded an effective magnetic moment of 1.78 μB for the V4+ cation. Short-range magnetic ordering was observed around 7 K. The susceptibility data were fit to the Heisenberg square-lattice model supporting that the short-range magnetic interactions are antiferromagnetic and two-dimensional. IR and thermal properties were also characterized.

A new noncentrosymmetric U4+-containing fluoride, U3F12(H2O), has been synthesized via a mild hydrothermal route and its crystal structure determined by single-crystal X-ray diffraction. The material exhibits a complex three-dimensional structure that is based on [U6F33(H2O)2)]9– hexanuclear building units consisting of corner- and edge-shared UF8, UF9, and UOF7 polyhedra. Powder second-harmonic generation (SHG) measurements revealed that the SHG efficiency for U3F12(H2O) is comparable to that of α-SiO2. Magnetic susceptibility measurements indicated that the U4+(f2)-containing material exhibits a singlet ground state at low temperature. IR and UV–vis reflectance spectra were obtained, and the thermal behavior was investigated by thermogravimetric analysis.

A series of seven compounds, Sr2Mn(OH)6, Ba2Mn(OH)6, Sr2Co(OH)6, Ba2Co(OH)6, Sr2Ni(OH)6, Ba2Ni(OH)6, and Ba2Cu(OH)6, were synthesized using a low-melting hydroflux, a hybrid approach between aqueous hydrothermal and molten hydroxide flux techniques. Crystals of the hexahydroxometallates were obtained by dissolving appropriate amounts of alkaline-earth nitrates or hydroxides and transition-metal oxides, acetates, or chlorides in the hydroflux and reacting at 180–230 °C. The isostructural compounds all crystallize in the monoclinic space group P21/n. The monoclinic structure consists of isolated transition-metal octahedra within a three-dimensional framework of corner- and edge-shared eight-coordinate, alkaline-earth polyhedra. Magnetic susceptibility data show that all compounds are simple paramagnets. Thermogravimetric analysis indicates that these hydroxides lose water between 215 and 350 °C and transform into oxide products, the identity of which depends on the metal cations present in the parent hexahydroxometallates.

Single crystals of complex uranium oxides, CaUO4, β-Ca3UO6, K4CaU3O12 and K4SrU3O12 were grown from carbonate melts. The crystal structures of the four uranates were determined by single crystal X-ray diffraction. CaUO4 crystallizes in the hexagonal space group R-3m, with lattice parameters a = 6.2570(7) Å and α = 36.04(2)°. The U6+ atom in CaUO4 is 8-coordinate and exhibits hexagonal bipyramidal geometry with six long and two short U–O bonds, typical of a uranyl species. β-Ca3UO6 forms in the monoclinic space group P21/n, with lattice parameters a = 5.728(1) Å, b = 5.956(1) Å, c = 8.298(2) Å, and β = 90.55(3)°, and adopts a distorted double perovskite structure. K4CaU3O12 and K4SrU3O12 crystallize in the cubic space group Im-3m with lattice parameters a = 8.483(1) Å and a = 8.582(1) Å, respectively. In all three perovskite-type oxides, the U(VI) cation is located in an octahedral coordination environment and exhibits typical uranyl geometry with four long and two short U–O bonds.Graphical abstractHighlights► Synthesis of CaUO4, Ca3UO6, and K4MU3O12 single crystals reported. ► K2CO3 employed for flux crystal growth. ► Ordered perovskite family oxides presented. ► Single crystal structures discussed.

Single crystals of Na4.5Nd0.5UO6 were grown out of a molten hydroxide flux and characterized by single crystal X-ray diffraction. Na4.5Nd0.5UO6 crystallizes in the orthorhombic space group Fddd with a = 6.6574(5) Å, b = 9.7031(6) Å, and c = 20.1571(13) Å. The material exhibits an ordered rock salt structure type. The uranium atoms are located in a distorted UO6 octahedral coordination environment containing two short, 2.056(4) Å, and four long, 2.116(3) Å, U–O bonds. The short bonds are significantly longer compared to what is typically observed for the uranyl cation, UO22+.

A new complex, Na2(H2O)2UO2(PDC)2 (1), has been synthesized from the ligand pyridine-2,5-dicarboxylic acid (H2PDC) and uranyl acetate. The crystal structure of compound 1 was determined by single-crystal diffraction. The compound crystallizes in the triclinic space group P-1, with a = 8.0606(6) Å, b = 11.3274(8) Å, c = 11.6584(8) Å, α = 116.7790(10)°, β = 107.4170(10)°, and γ = 90.9540(10)°. Compound 1 was further characterized by powder X-ray diffraction, luminescence spectroscopy, and UV–vis absorbance spectroscopy.

Six members of a new family of cerium-halide-based materials with promising scintillation behavior have been synthesized in single crystal form, and their crystal structures were determined. Specifically, these new compounds are [(CeCl3)7(BuOH)16(H2O)2]·(BuOH)2 (1), (CeBr3)14(BuOH)36 (2), [(CeCl3)7(1-PrOH)16(H2O)2]·(1-PrOH)2 (3), [(CeBr3)7(1-PrOH)18]·(1-PrOH)2 (4), [(CeCl3)6(iBuOH)15]·(iBuOH)2 (5), and CeCl3(sec-BuOH)2(H2O) (6). Additionally, the scintillation ability of compound 1 was established. The structures of these cerium-halide-based materials consist of catenated tetradecanuclear rings that arrange themselves into three distinct structural motifs which contain the largest lanthanide-based ring structures reported to date; the different motifs are obtained by involving specific alcohols during synthesis. Specifically, n-butanol and n-propanol lead to 1-D chains of tetradecanuclear rings, and iso-butanol leads to 2-D parquet-patterned sheets of rectangular tetradecanuclear rings, while sec-butanol results in a zigzag 1-D chain structure. One of the compounds, [(CeCl3)6(iBuOH)15]·(iBuOH)2, has been shown to scintillate with a light yield of up to 1920 photons/MeV, and due to the presence of protons, it should be capable of detecting high energy neutrons without the necessity of prior thermalization. Furthermore, it also appears to be the first cerium-based compound that scintillates in spite of the fact that water coordinates to two of the Ce(III) centers within the structure.

Two main group coordination compounds, Pb(NO2TA) (1) and [In(OH)(NO2TA)]·(H2O)2.99(7) (2) were grown as single crystals via hydrothermal synthesis (NO2TA = nitro-terephthalate). Coordination polymer 1 crystallizes in the monoclinic space group P21/c, and forms a layered structure in which lead atoms are bridged or pillared by four symmetry-equivalent ligands. Framework 2 crystallizes in the orthorhombic space group Imma and forms a 3-D material with rhombic channels along the b axis direction, which are filled with disordered water molecules.Graphical abstractHighlights► New indium and lead nitro-terephthalate coordination compounds. ► Structural comparison with known bismuth and uranium nitro-terephthalate coordination compounds. ► Cations influence formation of clusters, layers, solvent-filled channels, or non-porous frameworks. ► Ligand-to-metal charge transfer based luminescence is quenched by the nitro-group.

The asymmetrically substituted heterocyclic alkyne 5-(pyridin-3-ylethynyl) picolinate (P3PA) was synthesized via a one-pot Sonogashira coupling. After purification, P3PA was reacted with Pb(NO3)2 into the two-dimensional coordination polymer Pb(P3PA)2(H2O)2 (1) under hydrothermal conditions. Coordination polymer 1 crystallizes into the monoclinic space group I2/a, with a = 15.5775(10) Å, b = 5.9949(4) Å, c = 24.8380(16) Å, and β = 90.7500(10)°. In addition, the luminescent fluorene-based ligands, fluorene-9-carboxylate (FCA) and fluorenone-2,7-dicarboxylate (FDCA), were incorporated into hybrid materials via coordination to the lead (II) cation. Coordination polymer Pb(FCA)2 (2) crystallizes in the monoclinic space group P21/c (a = 8.0518(9) Å, b = 25.338(3) Å, c = 10.5842(12) Å, β = 94.913(2)°), and forms a 1-D polymeric chain. Coordination polymer Pb3(FDCA)3(H2O)3 (3) crystallizes in the triclinic space group P1 (a = 6.6990(5) Å, b = 10.1529(7) Å, c = 13.6935(9) Å, α = 81.884(2)°, β = 87.260(2)°, γ = 84.399(2)°), and forms pillared 3-D layers. These three compounds have been identified via single crystal X-ray diffraction and characterized via powder X-ray diffraction, UV–Vis spectroscopy, and fluorescence spectroscopy.Graphical abstractHighlights► Three lead coordination compounds based on conjugated organic ligands are reported. ► One lead-containing complex was obtained using 5-(pyridin-3-ylethynyl) picolinate. ► Lead-containing chain and sheet structure was obtained. ► Optimal hydro-/solvo-thermal conditions were established. ► Ligand based fluorescent properties were investigated.

Pr2Cl6(CH3OH)8 (1), Pr2Cl6((CH3)2CHOH)8 (2) and (PrCl3)7(CH3CH2CH2OH)18·(CH3CH2CH2OH) (3) were synthesized via slow evaporation of a supersaturated solution of PrCl3 in methanol, isopropanol and n-propanol respectively. The crystal structures were determined, revealing two very different topological arrangements. The evaporation in the presence of methanol and isopropanol lead to dimeric molecular adducts, while n-propanol leads to the formation of 1-D chains of tetradecanuclear rings. The molecular adducts are held together via edge sharing polyhedra while the rings are held together via edge- and face-sharing polyhedra. The absorbance and luminescence of these compounds was also investigated.Graphical abstractHighlights► Three novel structures incorporating PrCl3, in dimeric adducts or 1-D polymeric chains of rings. ► Topological control via the coordinating crystallization solvent, yielding unique topologies. ► Tetradecanuclear ring structure incorporating 14 Pr (III) cations via bridging chloride anions. ► Absorbance measurements suggest, that these species may be forming in solution at higher concentrations. ► Three luminescent compounds, optical properties investigated.

The coordination framework [Co2(H2O)2(pyrazine)V4O12](H2O)2 (1) was synthesized via hydrothermal synthesis using cobalt nitrate, vanadium oxide, and pyrazine. Compound 1 crystallizes in the monoclinic space group P21/n (a = 7.172(3) Å, b = 9.907(4) Å, c = 12.211(4) Å, and β = 105.301(7)°) and contains a rare V4O12 trigonal bipyramidal double chain.

The coordination polymers [Co2(N3)2(BZA)4(H2O)]·EtOH (1) and Cu(N3)(BZA)2(H2O) (2) were synthesized via room temperature diffusion layering using 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (N3), cobalt nitrate, copper acetate, and sodium benzoate (NaBZA). Compound 1 crystallizes in the monoclinic C2/c space group with unit cell dimensions of a = 15.8952(6) Å, b = 13.9127(6) Å, c = 24.2984(10) Å, and β = 100.595(1)°. Compound 2 crystallizes in the orthorhombic Pna21 space group with unit cell dimensions of a = 22.211(3) Å, b = 5.9543(7) Å, and c = 18.038(2) Å. The coordination polymer Cu(N3)(SUCC)(H2O)2 (3) was synthesized via room temperature diffusion layering using 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (N3), copper acetate, and sodium succinate (NaSUCC). Compound 3 crystallizes in the monoclinic P21/n space group with unit cell dimensions of a = 8.8148(7) Å, b = 8.7643(7) Å, c = 11.7758(9) Å, and β = 102.6990(10)°.

Two lead coordination compounds, Pb(PYTAC)2 (1), and Pb(PYTAC)2(NO3) (2), were grown as single crystals via hydrothermal synthesis (PYTAC = 2-(4-pyridyl) thiazole-4-carboxylate). Both compounds have been identified via single crystal X-ray diffraction. Coordination polymer 1 crystallizes in a triclinic space group P-1 (a = 5.5097(4) Å, b = 7.2822(5) Å, c = 11.3134(8) Å, α = 103.5580(10)°, β = 99.4330(10)°, γ = 97.1050(10)°), and forms 2-D layers parallel to the crystallographic (ac) plane. Coordination polymer 2 crystallizes in a triclinic space group P-1 (a = 9.8102(5) Å, b = 10.5972(6) Å, c = 14.8076(8) Å, α = 91.9350(10)°, β = 100.8050(10)°, γ = 103.1350(10)°), and forms an infinite 1-D chains along the a axis.

Single crystals of the NaLnTiO4 (Ln = La, Pr, Nd) phases were grown out of reactive sodium hydroxide melts. These layered materials crystallize in space group P4/nmm of the tetragonal system, with unit cell dimensions of a = 3.7998(5) Å and c = 13.273(3) Å (La), a = 3.7686(5) Å and c = 12.940(3) Å (Pr), and a = 3.7551(5) Å and c = 12.848(3) Å (Nd). These compounds possess a layered structure that is a variant of K2NiF4 with ordering of the Na and Ln ions.

Crystallographic structural changes were investigated for Sr2Fe1.5Mo0.5O6−δ, an electrode material for symmetric solid oxide fuel cells. The samples of this material were heated and cooled in wet hydrogen and wet oxygen atmospheres, to simulate the reducing and oxidizing conditions experienced under actual fuel cell operating conditions, and their structures and oxygen contents were determined using in situ powder neutron diffraction. The existence of a reversible tetragonal to cubic phase transition was established to occur between room temperature and 400 °C, both on heating and cooling in either oxygen or hydrogen. The oxygen content reaches a low value of 5.50(2) at 850 °C in wet hydrogen. Excellent correlations are observed between the oxygen content of the structure and the conductivities reported in the literature.

Single crystals of five transition metal uranium fluorides were obtained via the use of a mild hydrothermal route. Uranyl acetate was used as both the uranium source and the reducing agent for an in situ reduction of U(VI) to U(IV). The synthesized materials are present as both two- and three-dimensional structures and contain uranium in 9-fold coordination environments. Magnetic susceptibility measurements indicate that the reported materials remain paramagnetic down to 2 K, with no evidence for the existence of long-range magnetic ordering. Thermogravimetric analysis studies of the reported materials are also presented.