白果形钨酸铅的可控合成及光致发光特性

以酒石酸钠为表面活性剂,采用直接沉淀法合成了白果形钨酸铅晶体,通过扫描电子显微镜(SEM)、X射线衍射(XRD)、能量散射仪(EDS)及荧光发射光谱(PL)对产物的结构和性质进行了表征。探讨了酒石酸钠对(004)晶面的抑制作用以及pH值和陈化温度对产物形貌的影响,结合晶体的内部结构提出了产物可能的形成机制。结果表明,陈化温度为30℃时,晶体形貌最为规整,PbWO₄晶体在紫外光激发下展现出强的绿光发射,在pH=9时可达到最大的发光强度。     

One-dimensional chains in uranyl tungstates: Syntheses and structures of A8[(UO2)4(WO4)4(WO5)2] (A=Rb, Cs) and Rb6[(UO2)2O(WO4)4]

Three new uranyl tungstates, A₈[(UO₂)₄(WO₄)₄(WO₅)₂] (A=Rb (1), Cs (2)), and Rb₆[(UO₂)₂O(WO₄)₄] (3), were prepared by high-temperature solid-state reactions and their structures were solved by direct methods on twinned crystals, refined to R₁=0.050, 0.042, and 0.052 for 1, 2, and 3, respectively. Compounds 1 and 2 are isostructural, monoclinic P2₁/n, (1): a=11.100(7), b=13.161(9), , β=90.033(13)°, , Z=8 and (2): , , , β=89.988(2)°, , Z=8. There are four symmetrically independent U⁶⁺ sites that form linear uranyl [O=U=O]²⁺ cations with rather distorted coordination in their equatorial planes. There are six W positions: W(1) and W(2) have square-pyramidal coordination (WO₅), whereas W(3), W(4), W(5), and W(6) are tetrahedrally coordinated. The structures are based upon a novel type of one-dimensional (1D) [(UO₂)₄(WO₄)₄(WO₅)₂]⁴⁻ chains, consisting of WU₄O₂₅ pentamers linked by WO₄ tetrahedra and WO₅ square pyramids. The chains run parallel to the a-axis and are arranged in modulated pseudo-2D-layers parallel to (0 1 0). The A⁺ cations are in the interlayer space between adjacent pseudo-layers and provide a 3D integrity of the structures. Compounds 1 and 2 are the first uranyl tungstates with 2/3 of W atoms in tetrahedral coordination. Such a high concentration of low-coordinated W⁶⁺ cations is probably responsible for the 1D character of the uranyl tungstate units. The compound 3 is triclinic, P1¯ a=10.188(2), b=13.110(2), , α=97.853(3), β=96.573(3), γ=103.894(3)°, , Z=4. There are four U positions in the structure with a typical coordination of a pentagonal bipyramid that contain uranyl ions, UO₂²⁺, as apical axes. Among eight W sites, the W(1), W(2), W(3), W(4), W(5), and W(6) atoms are tetrahedrally coordinated, whereas the W(7) and W(8) cations have distorted fivefold coordination. The structure contains chains of composition [(UO₂)₂O(WO₄)₄]⁶⁻ composed of UO₇ pentagonal bipyramids and W polyhedra. The chains involve dimers of UO₇ pentagonal bipyramids that share common O atoms. The dimers are linked into chains by sharing corners with WO₄ tetrahedra. The chains are parallel to [−101] and are arranged in layers that are parallel to (1 1 1). The Rb⁺ cations provide linkage of the chains into a 3D structure. The compound 1 has many structural and chemical similarities to its molybdate analog, Rb₆[(UO₂)₂O(MoO₄)₄]. However, the compounds are not isostructural. Due to the tendency of the W⁶⁺ cations to have higher-than-fourfold coordination, part of the W sites adopt distorted fivefold coordination, whereas all Mo atoms in the Mo compound are tetrahedrally coordinated. Distribution of the WO₅ configurations along the chain extension does not conform to its ‘typical’ periodicity. As a result, both the chain identity period and the unit-cell volume are doubled in comparison to the Mo analog, which leads to a new structure type.     

白果形钨酸铅的可控合成及光致发光特性

以酒石酸钠为表面活性剂,采用直接沉淀法合成了白果形钨酸铅晶体,通过扫描电子显微镜(SEM)、X射线衍射(XRD)、能量散射仪(EDS)及荧光发射光谱(PL)对产物的结构和性质进行了表征。探讨了酒石酸钠对(004)晶面的抑制作用以及pH值和陈化温度对产物形貌的影响,结合晶体的内部结构提出了产物可能的形成机制。结果表明,陈化温度为30℃时,晶体形貌最为规整,PbWO4晶体在紫外光激发下展现出强的绿光发射,在pH=9时可达到最大的发光强度。     

Structural changes accompanying negative thermal expansion in Zr2(MoO4)(PO4)2

Zr₂(MoO₄)(PO₄)₂ is orthorhombic (Sc₂W₃O₁₂ structure) from 9 to at least 400 K, and shows anisotropic volume negative thermal expansion (α_a=−8.35(4)×10⁻⁶ K⁻¹; α_b=3.25(3)×10⁻⁶ K⁻¹; α_c=−8.27(5)×10⁻⁶ K⁻¹ in the range 122-400 K) similar in magnitude to A₂M₃O₁₂ (M—Mo or W) with large A³⁺. The contraction on heating is associated with a pattern of Zr-O-Mo/P bond angle changes that is somewhat similar, but not the same as that for Sc₂W₃O₁₂. On heating, the most pronounced reductions in the separation between the crystallographic positions of neighboring Zr and P are not associated with significant reductions in the corresponding Zr-O-P crystallographic bond angles, in contrast to what was seen for Sc₂W₃O₁₂.     

Hydrothermal synthesis, thermal, structural, spectroscopic and magnetic studies of the Mn5−xCox(HPO4)2(PO4)2(H2O)4 (x=1.25, 2, 2.5 and 3) finite solid solution

The Mn_5−xCo_x(HPO₄)₂(PO₄)₂(H₂O)₄ (x=1.25, 2, 2.5, 3) finite solid solution has been synthesized by mild hydrothermal conditions under autogeneous pressure. The phases crystallize in the C2/c space group with Z=4, belonging to the monoclinic system. The unit-cell parameters obtained from single crystal X-ray diffraction are: a=17.525(1), b=9.0535(6), c=9.4517(7) Å, β=96.633(5) ° being R1=0.0436, wR2=0.0454 for Mn75Co25; a=17.444(2), b=9.0093(9), c=9.400(1) Å, β=96.76(1) ° being R1=0.0381, wR2=0.0490 for Mn60Co40; a=17.433(2), b=8.9989(9), c=9.405(1) Å, β=96.662(9) ° being R1=0.0438, wR2=0.0515 for Mn50Co50 and a=17.4257(9), b=8.9869(5), c=9.3935(5) Å, β=96.685(4) ° being R1=0.0296, wR2=0.0460 for Mn40Co60. The structure consists of a three dimensional network formed by octahedral pentameric entities (Mn,Co)₅O₁₆(H₂O)₆ sharing vertices with the (PO₄)³⁻ and (HPO₄)²⁻ tetrahedra. The limit of thermal stability of these compounds is, approximately, 165 °C, near to this mean temperature the phases loose their water content in two successive steps. IR spectra show the characteristic bands of the water molecules and the phosphate and hydrogen-phosphate oxoanions. The diffuse reflectance spectra are consistent with the presence of MO₆ octahedra environments in slightly distorted octahedral geometry, except for the M(3)O₆ octahedron which presents a remarkable distortion and so a higher Dq parameter. The mean value for the Dq and B-Racah parameter for the M(1),(2)O₆ octahedra is 685 and 850 cm⁻¹, respectively. These parameters for the most distorted M(3)O₆ polyhedron are 825 and 880 cm⁻¹, respectively. The four phases exhibit antiferromagnetic couplings as the major magnetic interactions. However, a small spin canting phenomenon is observed at low temperatures for the two phases with major content in the anisotropic-Co(II) cation.     

Syntheses, crystal structures and spectroscopic properties of KEu[AsS4], K3Dy[AsS4]2 and Rb4Nd0.67[AsS4]2

Three rare earth compounds, KEu[AsS₄] (1), K₃Dy[AsS₄]₂ (2), and Rb₄Nd_0.67[AsS₄]₂ (3) have been synthesized employing the molten flux method. The reactions of A₂S₃ (A = K, Rb), Ln (Ln = Eu, Dy, Nd), As₂S₃, S were accomplished at 600 °C for 96 h in evacuated fused silica ampoules. Crystal data for these compounds are: 1, monoclinic, space group P2₁/m (no. 11), a = 6.7276(7) Å, b = 6.7190(5) Å, c = 8.6947(9) Å, β = 107.287(12)°, Z = 2; 2, monoclinic, space group C2/c (no. 15), a = 10.3381(7) Å, b = 18.7439(12) Å, c = 8.8185(6) Å, β = 117.060(7)°, Z = 4; 3, orthorhombic, space group Ibam (no. 72), a = 18.7333(15) Å, b = 9.1461(5) Å, c = 10.2060(6) Å, Z = 4. 1 is a two-dimensional structure with ²_∞[Eu(AsS₄)]⁻ layers separated by potassium cations. Within each layer, distorted bicapped trigonal [EuS₈] prisms are linked through distorted [AsS₄]³⁻ tetrahedra. Each Eu²⁺ cation is coordinated by two [AsS₄]³⁻ units by edge-sharing and bonded to further two [AsS₄]³⁻ units by corner-sharing. Compound 2 contains a one-dimensional structure with ¹_∞[Dy(AsS₄)₂]³⁻ chains separated by potassium cations. Within each chain, distorted bicapped trigonal prisms of [DyS₈] are linked by slightly distorted [AsS₄]³⁻ tetrahedra. Each Dy³⁺ ion is surrounded by four [AsS₄]³⁻ moieties in an edge-sharing fashion. For compound 3 also a one-dimensional structure with ¹_∞[Nd₀.₆₇(AsS₄)₂]⁴⁻ chains is observed. But the Nd position is only partially occupied and overall every third Nd atom is missing along the chain. This cuts the infinite chains into short dimers containing two bridging [As₄]³⁻ units and four terminal [AsS₄]³⁻ groups. 1 is characterized with UV/vis diffuse reflectance spectroscopy, IR, and Raman spectra.     

Crystal structures and thermal properties of Ba(1,2,4-t-Bu3C5H2)2 and Sr(1,2,4-t-Bu3C5H2)2: Precursors for atomic layer deposition

Sterically hindered Lewis base free bis(1,2,4-tri-tert-butylcyclopentadienyl)strontium (1) and bis(1,2,4-tri-tert-butylcyclopentadienyl)barium (2) were synthesized using the common metathesis route and characterized with NMR, MS, TGA/SDTA and XRD. Compound 1 crystallized as a monomer with typical bent structure. Asymmetric unit contains two independent slightly different Sr(t-Bu₃C₅H₂)₂ molecules with Cp(centroid)-Sr-Cp(centroid) angles of 165.1° and 169.4°. Depending on the way of crystallization two polymorphs (2a and 2b) were observed for Ba(t-Bu₃C₅H₂)₂. On sublimation Ba(t-Bu₃C₅H₂)₂ crystallizes as chains in which one methyl group of each Ba(t-Bu₃C₅H₂)₂ unit interacts with neighboring Ba(t-Bu₃C₅H₂)₂ unit’s barium atom. Slow crystallization of waxy evaporation residue of toluene solution results in monoclinic crystals (2b) whose asymmetric unit contains four slightly different individual Ba(t-Bu₃C₅H₂)₂ molecules with Cp(centroid)-Ba-Cp(centroid) angles of 161.3-164.9°. Both compounds prepared are volatile, thermally stable and reactive and thus suitable precursors for atomic layer deposition of thin films.     

Crystal structure and lattice dynamics of Sr3Y(BO3)3

X-ray, Raman and infrared (IR) studies of the Sr₃Y(BO₃)₃ (BOYS) single crystal grown by the Czochralski technique are presented. The crystal structure is trigonal, space group (no. 148), and comprises six formula units in the unit cell with the hexagonal axes a=12.527(2) and c=9.280(2) Å. The assignment of the observed vibrational modes is proposed on the basis of lattice dynamics calculations. The unusual large bandwidth of the internal modes and the enhancement of the principal mean square thermal displacements for BO₃ and Y(1) indicate that some type of disorder is present in the studied crystal.     

Synthesis, crystal structure, and nonlinear optical properties of Bi2Cu5B4O14

Bi₂Cu₅B₄O₁₄ crystallizes in the noncentrosymmetric triclinic space group P1 (No. 1) with cell parameters a=10.1381(11) Å, b=9.3917(11) Å, c=3.4566(4) Å, α=105.570(2)°, β=92.275(2)°, γ=107.783(2)°, Z=1 and R₁=0.0401 and wR₂=0.0980. It is a layered structure that is built up from sheets of rectangular CuO₄ and trigonal BO₃ groups. The sheets are connected by infinite chains of edge shared BiO₆ polyhedra that intersect the bc plane at an angle slightly greater than 90°. The second-harmonic generation efficiency of Bi₂Cu₅B₄O₁₄, using 1064 nm radiation, is about one half times that of KH₂PO₄.     

Syntheses, crystal structures and spectroscopic properties of Ag2Nb[P2S6][S2] and KAg2[PS4]

Ag₂Nb[P₂S₆][S₂] (1) was obtained from the direct solid state reaction of Ag, Nb, P₂S₅ and S at 500 °C. KAg₂[PS₄] (2) was prepared from the reaction of K₂S₃, Ag, Nd, P₂S₅ and extra S powder at 700 °C. Compound 1 crystallizes in the orthorhombic space group Pnma with a=12.2188(11), b=26.3725(16), c=6.7517(4) Å, V=2175.7(3) Å³, Z=8. Compound 2 crystallizes in the non-centrosymmetric tetragonal space group with lattice parameters a=6.6471(7), c=8.1693(11) Å, V=360.95(7) Å³, Z=2. The structure of Ag₂Nb[P₂S₆][S₂] (1) consists of [Nb₂S₁₂], [P₂S₆] and new found puckered [Ag₂S₄] chains which are along [001] direction. The Nb atoms are located at the center of distorted bicapped trigonal prisms. Two prisms share square face of two [S₂²⁻] to form one [Nb₂S₁₂] unit, in which Nb-Nb bond is formed. The [Nb₂S₁₂] units share all S²⁻ corners with ethane-like [P₂S₆] units to form 14-membered rings. The novel puckered [Ag₂S₄] chains are composed of distorted [AgS₄] tetrahedra and [AgS₃] triangles that share corners with each other. These chains are connected with [P₂S₆] units and [Nb₂S₁₂] units to form three-dimensional frame work. The structural skeleton of 2 is built up from [AgS₄] and [PS₄] tetrahedra linked by corner-sharing. The three-dimensional anionic framework contains orthogonal, intersecting tunnels directed along [100] and [010]. This compound possesses a compressed chalcopyrite-like structure. The structure is compressed along [001] and results from eight coordination sphere for K⁺. Both compounds are characterized with UV/vis diffuse reflectance spectroscopy and compound 1 with IR and Raman spectra.     

An investigation of the Nd2O3-MoO3 phase system: Thermal decomposition of Nd2Mo4O15 and formation of Nd6Mo10O39

A new neodymium molybdate, Nd₆Mo₁₀O₃₉, has been identified in the Nd₂O₃-MoO₃ phase system. Nd₆Mo₁₀O₃₉ appears to be a metastable phase, which does not form directly from a stoichiometric mixture of Nd₂O₃ and MoO₃ oxides. Instead, it can be obtained by thermal decomposition of Nd₂Mo₄O₁₅. Nd₂Mo₄O₁₅ usually decomposes into Nd₂(MoO₄)₃, and the formation of Nd₆Mo₁₀O₃₉ critically depends on the heating regime used.The structure of Nd₆Mo₁₀O₃₉ has been determined by single crystal X-ray diffraction. It crystallizes in the monoclinic space group C2/c, with unit cell parameters of , , , β=100.767(2)°, at 120 K. Nd atoms are seven and eight coordinate, and pairs of coordination polyhedra share edges and faces, respectively, to form Nd₂O₁₂ and Nd₂O₁₃ groups. All Mo atoms are in tetrahedral coordination environments, with some of the tetrahedra sharing corners to form pyromolybdate groups.     

Hydrothermal synthesis, crystal structure, thermal behavior, ferromagnetic resonance and ferrimagmetic behavior of (C4H12N2)1.5[Fe3(HAsO4)1.02(HPO4)0.98(AsO4)0.88(PO4)0.12F5]

(C₄H₁₂N₂)_1.5[Fe₃(HAsO₄)_1.02(HPO₄)_0.98(AsO₄)_0.88(PO₄)_0.12F₅] has been synthesized by using mild hydrothermal conditions under autogeneous pressure. The crystal structure was solved from X-ray single crystal data. The compound crystallizes in the monoclinic P2₁/c space group. The unit cell parameters are a=8.270(7), b=22.028(3), , β=99.79(2)° with Z=4. The crystal structure is formed from [Fe₃(HAsO₄)_1.02(HPO₄)_0.98(AsO₄)_0.88(PO₄)_0.12F₅]³⁻ sheets with the piperazinium cations located in the interlayer space, compensating the anionic charge and establishing hydrogen bonds. The IR and Raman spectroscopies confirm the existence of both the arsenate/hydrogenarsenate and phosphate/hydrogenphosphate oxoanions and the presence of the piperazinium dication. The reflectance diffuse spectrum is in good agreement with the existence of iron(III) high spin cations in slightly distorted octahedral geometry. The values of the Dq and Racah parameters are Dq=1005, B=1020 and . The ESR spectroscopy shows the presence of ferromagnetic resonance. The g-value shifts from 1.99(1) in the 300-15 K range to 3.11(1) at lower temperatures. Magnetic measurements indicate the presence of a ferrimagnetic behavior with the existence of a weak hysteresis loop at 5 K.     

Synthesis, crystal structure and NLO property of a nonmetal pentaborate [C6H13N2][B5O6(OH)4]

A nonmetal pentaborate [C₆H₁₃N₂][B₅O₆(OH)₄] (1) has been synthesized by 1,4-diazabicyclo[2.2.2] octane (DABCO) and boric acid, and characterized by single-crystal X-ray diffraction, FTIR, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic system with space group Cc (no. 9), a=10.205(2) Å, b=14.143(3) Å, c=11.003(2) Å, β=113.97(3)°, V=1451.1(5) Å³, Z=4. The anionic units, [B₅O₆(OH)₄]⁻, are interlinked via hydrogen bonding to form a three-dimensional (3D) supramolecular network containing large channels, in which the protonated [C₆H₁₃N₂]⁺ cations are located. Second-harmonic generation (SHG) measurements on the powder samples reveal that 1 exhibits SHG efficiency approximately 0.9 times that of potassium dihydrogen phosphate (KDP).     

Mild hydrothermal synthesis, crystal structure, thermal behaviour, spectroscopic and magnetic properties of (NH4)0.80Li0.20[Fe(AsO4)F]

The (NH₄)_0.80Li_0.20[Fe(AsO₄)F] compound has been synthesized under mild hydrothermal conditions. The compound crystallize in the orthorhombic Pna2₁ space group, with cell parameters a=13.352(9), b=6.7049(9), c=10.943(2) Å and Z=8. The compound belongs to the KTiO(PO₄) structure type, with chains alternating FeO₄F₂ octahedra and AsO₄ tetrahedra, respectively, running along the “a” and “b” crystallographic axes. The diffuse reflectance spectrum in the visible region shows the forbidden electronic transitions characteristic of the Fe(III) d⁵-high spin cation in slightly distorted octahedral geometry. The Mössbauer spectrum at room temperature is characteristic of iron (III) cations. The ESR spectra, carried out from room temperature to 200 K, remain isotropic with variation in temperature; the g-value being 1.99(1). Magnetic measurements indicate the predominance of strong antiferromagnetic interactions.     

Original close-packed structure and magnetic properties of the Pb4Mn9O20 manganite

The crystal structure of the Pb₄Mn₉O₂₀ compound (previously known as “Pb_0.43MnO_2.18”) was solved from powder X-ray diffraction, electron diffraction, and high resolution electron microscopy data (S.G. Pnma, a=13.8888(2) Å, b=11.2665(2) Å, c=9.9867(1) Å, R_I=0.016, R_P=0.047). The structure is based on a 6H (cch)₂ close packing of pure oxygen “h”-type (O₁₆) layers alternating with mixed “c”-type (Pb₄O₁₂) layers. The Mn atoms occupy octahedral interstices formed by the oxygen atoms of the close-packed layers. The MnO₆ octahedra share edges within the layers, whereas the octahedra in neighboring layers are linked through corner sharing. The relationship with the closely related Pb₃Mn₇O₁₅ structure is discussed. Magnetization measurements reveal a peculiar magnetic behavior with a phase transition at 52 K, a small net magnetization below the transition temperature, and a tendency towards spin freezing.     

Structural and vibrational studies of Li[Kx(NH4)1−x]SO4 and Li2KNH4(SO4)2 mixed crystals

Mixed crystals of Li[K_x(NH₄)_1−x]SO₄ have been obtained by evaporation from aqueous solution at 313 K using different molar ratios of mixtures of LiKSO₄ and LiNH₄SO₄. The crystals were characterized by Raman scattering and single-crystal and powder X-ray diffraction. Two types of compound were obtained: Li[K_x(NH₄)_1−x]SO₄ with x?0.94 and Li₂KNH₄(SO₄)₂. Different phases of Li[K_x(NH₄)_1−x]SO₄ were yielded according to the molar ratio used in the preparation. The first phase is isostructural to the room-temperature phase of LiKSO₄. The second phase is the enantiomorph of the first, which is not observed in pure LiKSO₄, and the last is a disordered phase, which was also observed in LiKSO₄, and can be assumed as a mixture of domains of two preceding phases. In the second type of compound with formula Li₂KNH₄(SO₄)₂, the room-temperature phase is hexagonal, symmetry space group P6₃ with cell-volume nine times that of LiKSO₄. In this phase, some cavities are occupied by K⁺ ions only, and others are occupied by either K⁺ or NH₄⁺ at random. Thermal analyses of both types of compounds were performed by DSC, ATD, TG and powder X-ray diffraction. The phase transition temperatures for Li[K_x(NH₄)_1−x]SO₄x?0.94 were affected by the random presence of the ammonium ion in this disordered system. The high-temperature phase of Li₂KNH₄(SO₄)₂ is also hexagonal, space group P6₃/mmc with the cell a-parameter double that of LiKSO₄. The phase transition is at 471.9 K.     

Structure, energy band, and optical properties of NaLa(PO3)4 crystal

An alkali metal-rare earth phosphate crystal of NaLa(PO₃)₄ has been synthesized by high temperature solid-state reactions and structurally characterized by single crystal X-ray diffraction analysis, for the first time. It crystallizes in the monoclinic P2₁/n space group with lattice parameters: a=7.2655(3), b=13.1952(5), , β=90.382°(1), , Z=4. It is composed of LaO₈ polyhedra and [(PO₃)₄]⁴⁻ chains sharing oxygen atoms to form a three-dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The IR spectrum, absorption spectrum, and emission spectrum of the compound have been investigated. The absorption edge is located at 340 nm (3.60 eV). The calculated total and partial densities of states indicate that the top of valence bands is mainly built upon O-2p states which interact with P-3p states via σ (P-O) interactions, and the low conduction bands mostly originates from unoccupied La-5d states. The P-O bond is mostly covalent in character, and the ionic character of the Na-O bond is larger than that in the La-O bond.     

Preparation, crystal structure and thermal expansion of a new bismuth barium borate, BaBi2B4O10

Single crystals of a new compound, BaBi₂B₄O₁₀ were grown by cooling a melt with the stoichiometric composition. The crystal structure of the compound has been solved by direct methods and refined to R₁=0.049 (wR=0.113) on the basis of 1813 unique observed reflections (|F_o|>4σ|F_o|). It is monoclinic, space group P2₁/c, a=10.150(2), b=6. 362(1), c=12.485(2) Å, β=102.87(1)^o, V=786.0(2) Å³, Z=4. The structure is based upon anionic thick layers that are parallel to (001). The layers can be described as built from alternating novel borate [B₄O₁₀]⁸⁻_∞ chains and bismuthate [Bi₂O₅]⁴⁻_∞ chains extended along b-axis. The borate chains are composed of [B₃O₈]⁷⁻ triborate groups of three tetrahedra and single triangles with a [BO₂]⁻ radical. The borate chains are interleaved along the c-axis with rows of the Ba²⁺ cations so that the Ba atoms are located within the layers. The layers are connected by two nonequivalent Ba-O bonds as well as by two equivalent Bi-O bonds with bond valences in the range of 0.2-0.3 v.u.Thermal expansion of BaBi₂B₄O₁₀ studied by high-temperature X-ray powder diffraction in the temperature range of 20-700 °C (temperature step 30-35 °C) is highly anisotropic. While the b and c unit-cell parameters increase almost linearly on heating, temperature dependencies of a parameter and β monoclinic angle show nonlinear behavior. As a result, on heating orientation of thermal expansion tensor changes, and bulk thermal expansion increases from 20×10⁻⁶ °C⁻¹ at the first heating stage up to 57×10⁻⁶ °C⁻¹ at 700 °C that can be attributed to the increase of thermal mobility of heavy Bi³⁺ and Ba²⁺ cations.     

Synthesis, crystal structures, phase transition characterization and thermal decomposition of a new dabcodiium hexaaquairon(II) bis(sulfate): (C6H14N2)[Fe(H2O)6](SO4)2

The crystal structures of 1,4-diazabicyclo[2.2.2]octane (dabco)-templated iron sulfate, (C₆H₁₄N₂)[Fe(H₂O)₆](SO₄)₂, were determined at room temperature and at −173 °C from single-crystal X-ray diffraction. At 20 °C, it crystallises in the monoclinic symmetry, centrosymmetric space group P2₁/n, Z=2, a=7.964(5), b=9.100(5), c=12.065(5) Å, β=95.426(5)° and V=870.5(8) ų. The structure consists of [Fe(H₂O)₆]²⁺ and disordered (C₆H₁₄N₂)²⁺ cations and (SO₄)²⁻ anions connected together by an extensive three-dimensional H-bond network. The title compound undergoes a reversible phase transition of the first-order at −2.3 °C, characterized by DSC, dielectric measurement and optical observations, that suggests a relaxor–ferroelectric behavior. Below the transition temperature, the compound crystallizes in the monoclinic system, non-centrosymmetric space group Cc, with eight times the volume of the ambient phase: a=15.883(3), b=36.409(7), c=13.747(3) Å, β=120.2304(8)°, Z=16 and V=6868.7(2) ų. The organic moiety is then fully ordered within a supramolecular structure. Thermodiffractometry and thermogravimetric analyses indicate that its decomposition proceeds through three stages giving rise to the iron oxide.     

Syntheses and crystal structures of two new hydrated borates, Zn8[(BO3)3O2(OH)3] and Pb[B5O8(OH)]·1.5H2O

Two new hydrated borates, Zn₈[(BO₃)₃O₂(OH)₃] and Pb[B₅O₈(OH)]·1.5H₂O, have been prepared by hydrothermal reactions at 170 °C. Single-crystal X-ray structural analyses showed that Zn₈[(BO₃)₃O₂(OH)₃] crystallizes in a non-centrosymmetric space group R32 with a=8.006(2) Å, c=17.751(2) Å, Z=3 and Pb[B₅O₈(OH)]·1.5H₂O in a triclinic space group P1¯ with a=6.656(2) Å, b=6.714(2) Å, c=10.701(2) Å, α=99.07(2)°, β=93.67(2)°, γ=118.87(1)°, Z=2. Zn₈[(BO₃)₃O₂(OH)₃] represents a new structure type in which Zn-centered tetrahedra are connected via common vertices leading to helical ribbons _∞¹[Zn₈O₁₅(OH)₃]¹⁷⁻ that pack side by side and are further condensed through sharing oxygen atoms to form a three-dimensional _∞³[Zn₈O₁₁(OH)₃]⁹⁻ framework. The boron atoms are incorporated into the channels in the framework to complete the final structure. Pb[B₅O₈(OH)]·1.5H₂O is a layered compound containing double ring [B₅O₈(OH)]²⁻ building units that share exocyclic oxygen atoms to form a two-dimensional layer. Symmetry-center-related layers are stacked along the c-axis and held together by interlayer Pb²⁺ ions and water molecules via electrostatic and hydrogen bonding interactions. The IR spectra further confirmed the existence of both triangular BO₃ and OH groups in Zn₈[(BO₃)₃O₂(OH)₃], and BO₃, BO₄, OH groups as well as guest water molecules in Pb[B₅O₈(OH)]·1.5H₂O.