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1.
The reactions of UO3 and TeO3 with KCl, RbCl, or CsCl at 800 °C for 5 d yield single crystals of A2[(UO2)3(TeO3)2O2] (A=K (1), Rb (2), and Cs (3)). These compounds are isostructural with one another, and their structures consist of two-dimensional sheets arranged in a stair-like topology separated by alkali metal cations. These sheets are comprised of zigzagging uranium(VI) oxide chains bridged by corner-sharing trigonal pyramidal TeO32− anions. The chains are composed of dimeric, edge-sharing, pentagonal bipyramidal UO7 moieties joined by edge-sharing tetragonal bipyramidal UO6 units. The lone-pair of electrons from the TeO3 groups are oriented in opposite directions with respect to one another on each side of the sheets rendering each individual sheet non-polar. The alkali metal cations form contacts with nearby tellurite oxygen atoms as well as with oxygen atoms from the uranyl moieties. Crystallographic data (193 K, MoKα, ): 1, triclinic, space group , , , , α=101.852(1)°, β=102.974(1)°, γ=100.081(1)°, , Z=2, R(F)=2.70% for 98 parameters and 1697 reflections with I>2σ(I); 2, triclinic, space group , , , , α=105.590(2)°, β=101.760(2)°, γ=99.456(2)°, , Z=2, R(F)=2.36% for 98 parameters and 1817 reflections with I>2σ(I); 3, triclinic, space group , , , , α=109.301(1)°, β=100.573(1)°, γ=99.504(1)°, , Z=2, R(F)=2.61% for 98 parameters and 1965 reflections with I>2σ(I).  相似文献   

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The uranyl vanadates A2(UO2)3(VO4)2O (A=Li, Na) have been synthesized by solid-state reaction and the structure of the Li compound was solved from single-crystal X-ray diffraction. The crystal structure is built from chains of edge-shared U(2)O7 pentagonal bipyramids alternatively parallel to - and -axis and further connected together to form a three-dimensional (3-D) arrangement. The perpendicular chains are hung on both sides of a sheet parallel to (001), formed by U(1)O6 square bipyramids connected by VO4 tetrahedra, and derived from the autunite-type sheet. The resulting 3-D framework creates non-intersecting channels running down the - and -axis formed by empty face-shared oxygen octahedra, the Li+ ions are displaced from the center of the channels and occupy the middle of one edge of the common face. The peculiar position of the Li+ ion together with the full occupancy explain the low conductivity of Li2(UO2)3(VO4)2O compared with that of Na(UO2)4(VO4)3 containing the same type of channels half occupied by Na+ ions in the octahedral sites.Crystallographic data for Li2(UO2)3(VO4)2O: tetragonal, space group I41/amd, , , , Z=4, ρmes=5.32(2) g/cm3, ρcal=5.36(3) g/cm3, full-matrix least-squares refinement basis on F2 yielded, R1=0.032, wR2=0.085 for 37 refined parameters with 364 independent reflections with I?2σ(I).  相似文献   

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The rare-earth dicyanamides Ln[N(CN)2]3 (Ln=La, Ce, Pr, Nd, Sm, Eu) were obtained via ion exchange in aqueous medium and subsequent drying: The crystal structures were solved and refined based on X-ray powder diffraction data and they were found to be isotypic: Ln[N(CN)2]3; Cmcm (no. 63), Z=4, Ln=La: , , ; Ce: , , ; Pr: , , ; Nd: , , ; Sm: , , ; Eu: , , ). The compounds represent the first dicyanamides with trivalent cations. The Ln3+ ions are coordinated by three bridging N atoms and six terminal N atoms of the dicyanamide ions forming a three capped trigonal prism. The structure type is related to that of PuBr3. The novel compounds Ln[N(CN)2]3 have been characterized by IR and Raman spectroscopy (Ln=La) and the thermal behavior has been monitored by differential scanning calorimetry (Ln=Ce, Nd, Eu).  相似文献   

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The crystal structures of the title compounds were solved using the single-crystal X-ray diffraction technique. At room temperature CsKSO4Te(OH)6 was found to crystallize in the monoclinic system with Pn space group and lattice parameters: ; ; ; β=106.53(2)°; ; Z=4 and . The structural refinement has led to a reliability factor of R1=0.0284 (wR2=0.064) for 7577 independent reflections. Rb1.25K0.75SO4Te(OH)6 material possesses a monoclinic structure with space group P21/a and cell parameters: ; ; ; β=106.860(10)°; ; Z=4 and . The residuals are R1=0.0297 and wR2=0.0776 for 3336 independent reflections. The main interest of these structures is the presence of two different and independent anionic groups (TeO66− and SO42−) in the same crystal.Complex impedance measurements (Z*=ZiZ) have been undertaken in the frequency and temperature ranges 20-106 Hz and 400-600 K, respectively. The dielectric relaxation is studied in the complex modulus formalism M*.  相似文献   

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The crystal structures of three new intermetallic ternary compounds in the LnNiSb3 (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb3, NdNiSb3 and SmNiSb3 all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb6 octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb3), 4.6 K (NdNiSb3), and 2.9 K (SmNiSb3). Effective moments of 3.62 μB, 3.90 μB and 0.80 μB are found for PrNiSb3, NdNiSb3 and SmNiSb3, respectively, and are consistent with Pr3+ (f 2), Nd3+ (f 3), and Sm3+ (f 4).  相似文献   

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Two new aluminotriphosphates, RbAl3(P3O10)2 and CsAl3(P3O10)2, were synthesized by solid-state reaction. They crystallize in non-centrosymmetric space groups: C2221 with , , , (Z=4) for RbAl3(P3O10)2 and C2ce with , , , (Z=4) for CsAl3(P3O10)2. Their 3D frameworks, built up of corner sharing P3O10 groups, AlO4 tetrahedra and AlO6 octahedra, exhibit several remarkable features. The AlO4 tetrahedra and P3O10 groups are directly associated through the corners, forming helical columns in the Rb-phase and “helicoid” layers in the Cs-phase. The simultaneous presence of AlO4 and AlO6 species, rather rare in phosphates, leads to the formation of closely related [Al3P6O24] layers in both structures, which differ by their stacking mode. The presence of intersecting tunnels running along 〈110〉 and [001] directions, with Rb+ and Cs+ sitting at the intersections, shows the opened character of these two structures.  相似文献   

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The single crystals of lanthanum metaphosphate MLa(PO3)4 (M=Na, Ag) have been synthesized and studied by a combination of X-ray crystal diffraction and vibrational spectroscopy. The sodium and silver compounds crystallize in the same monoclinic P21/n space group ( factor group) with the following respective unit cell dimensions: a=7.255(2), b=13.186(3), , β=90.40(2)°, , Z=4 and a=7.300(5), b=13.211(9), , β=90.47(4)°, , Z=4. This three-dimensional framework is built of twisted zig-zag chains running along a direction and made up of PO4 tetrahedra sharing two corners, connected to the LaO8 and NaO7 or AgO7 polyhedra by common oxygen atoms to the chains. The infrared and Raman vibrational spectra have been investigated. A group factor analysis leads to the determination of internal modes of (PO3) anion in the phosphate chain.  相似文献   

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Three manganese oxalates have been hydrothermally synthesized, and their structures determined by single-crystal X-ray diffraction. MnC2O4·2H2O (I) is orthorhombic, P212121, , , , , Z=4, final R, Rw=0.0832, 0.1017 for 561 observed data (I>3σ(I)). The one-dimensional structure consists of chains of oxalate-bridged manganese centers. [C4H8(NH2)2][Mn2(C2O4)3] (II) is triclinic, , , , , α=81.489(2)°, β=81.045(2)°, γ=86.076(2)°, , Z=1, final R, Rw=0.0467, 0.0596 for 1773 observed data (I > 3σ (I)). The three-dimensional framework is constructed from seven coordinate manganese and oxalate anions. The material contains extra-framework diprotonated piperazine cations. Mn2(C2O4)(OH)2 (III) is monoclinic, P21/c, , , , β=91.10(3)°, , Z=1, final R1, wR2=0.0710, 0.1378 for 268 observed data (I>2σ (I)). The structure is also three dimensional, with layers of MnO6 octahedra pillared by oxalate anions. The hydroxide group is found bonded to three manganese centers resulting in a four coordinate oxygen.  相似文献   

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Three new hydrated scandium selenites have been hydrothermally synthesized as single crystals and structurally and physically characterized. Sc2(SeO3)3·H2O crystallizes as a new structure type containing novel ScO7 pentagonal bipyramidal and ScO6+1 capped octahedral coordination polyhedra. Sc2(SeO3)3·3H2O contains typical ScO6 octahedra and is isostructural with its M2(SeO3)3·3H2O (M=Al, Cr, Fe, Ga) congeners. CsSc3(SeO3)4(HSeO3)2·2H2O contains near-regular ScO6 octahedra and has essentially the same structure as its indium-containing analogue. All three phases contain the expected pyramidal [SeO3]2- selenite groups. Crystal data: Sc2(SeO3)3·3H2O, Mr=524.85, trigonal, R3c (No. 161), , , , Z=6, R(F)=0.018, wR(F2)=0.036; Sc2(SeO3)3·H2O, Mr=488.82, orthorhombic, P212121 (No. 19), , , , , Z=4, R(F)=0.051, wR(F2)=0.086; CsSc3(SeO3)4(HSeO3)2·2H2O, Mr=1067.60, orthorhombic, Pnma (No. 62), , , , , Z=4, R(F)=0.035, wR(F2)=0.070.  相似文献   

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The disordered structures and low temperature dielectric relaxation properties of Bi1.667Mg0.70Nb1.52O7 (BMN) and Bi1.67Ni0.75Nb1.50O7 (BNN) misplaced-displacive cubic pyrochlores found in the Bi2O3-MIIO-Nb2O5 (M=Mg, Ni) systems are reported. As for other recently reported Bi-pyrochlores, the metal ion vacancies are found to be confined to the pyrochlore A site. The B2O6 octahedral sub-structure is found to be fully occupied and well-ordered. Considerable displacive disorder, however, is found associated with the O′A2 tetrahedral sub-structure in both cases. The A-site ions were displaced from Wyckoff position 16d (, , ) to 96 h (, , ) while the O′ oxygen was shifted from position 8b (, , ) to Wyckoff position 32e (, , ). The refined displacement magnitudes off the 16d and 8b sites for the A and O′ sites were 0.408 Å/0.423 Å and 0.350 Å/0.369 Å for BMN/BNN, respectively.  相似文献   

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The two compounds RbInS2 and RbInSe2 have been synthesized at 773 K by means of the reactive flux method. These isostructural compounds crystallize in space group C2/c of the monoclinic system with 16 formula units in a cell at 153 K of dimensions , , , and β=100.244(1)° for RbInS2, and , , , and β=100.16(2)° for RbInSe2. The In atoms are four-coordinated. The structure consists of two-dimensional (Q=S, Se) layers perpendicular to [001] separated from the Rb+ cations. Adamantane-like In4Q10 units are connected by common corners to form the layers. Band structure calculations indicate that these compounds are direct band-gap semiconductors with the smallest band gap at the Γ point. The calculated band gaps are 2.8 eV for RbInS2 and 2.0 eV for RbInSe2, values that are consistent with the colors of the compounds.  相似文献   

18.
The reaction of UO3 and TeO3 with a KCl flux at 800 °C for 3 days yields single crystals of K4[(UO2)5(TeO3)2O5]. The structure of the title compound consists of layered, two-dimensional sheets arranged in a stair-like topology separated by potassium cations. Contained within these sheets are one-dimensional uranium oxide ribbons consisting of UO7 pentagonal bipyramids and UO6 tetragonal bipyramids. The ribbons are in turn linked by corner-sharing with trigonal pyramidal TeO3 units to form sheets. The lone-pair of electrons from the TeO3 groups are oriented in opposite directions with respect to one another on each side of the sheets rendering each individual sheet nonpolar. The potassium cations form contacts with nearby tellurite units and axial uranyl oxygen atoms. Crystallographic data (193 K, MoKα, ): triclinic, space group , , , , α=99.642(1)°, β=93.591(1)°, γ=100.506(1)°, , Z=1,R(F)=4.19% for 149 parameters and 2583 reflections with I>2σ(I).  相似文献   

19.
The compound CsAgSb4S7 has been synthesized by the reaction of the elements in a Cs2S3 flux at 773 K. The compound crystallizes in a new structure type with eight formula units in space group C2/c of the monoclinic system in a cell at 153 K of dimensions , , , β=97.650(1)°, and . The structure contains two-dimensional layers separated by Cs atoms. Each layer is built from edge-sharing one-dimensional and chains. Each Ag atom is tetrahedrally coordinated to four S atoms. Each Sb3+ center is pyramidally coordinated to three S atoms to form an SbS3 group. CsAgSb4S7 is insulating with an optical band gap of 2.04 eV. Extended Hückel calculations indicate that the band gap in CsAgSb4S7 is dominated by the Sb 5s and S 3p states above and below the Fermi level.  相似文献   

20.
Two alkali metal uranates Rb2U2O7 and Rb8U9O31 have been synthesized by solid state reaction at high temperature and their crystal structures determined from single crystal X-ray diffraction data, collected with a three circles Brucker SMART diffractometer equipped by Mo(Kα) radiation and a charge-coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least-square method on the basis of F2 for all unique reflections, with R1=0.043 for 53 parameters and 746 independent reflections with I?2σ(I) for Rb2U2O7, monoclinic symmetry, space group P21/c, , , , β=108.81(1)°, , , Z=2 and R1=0.036 for 141 parameters and 2065 independent reflections with I?2σ(I) for Rb8U9O31, orthorhombic, space group Pbna, , , , , , Z=4.The Rb2U2O7 structure presents a strong analogy with that of K2U2O7 and can be described by layers of distorted UO2(O4) octahedra built from dimeric units of edge shared octahedra further linked together by opposite corners. In Rb8U9O31 puckered layers are formed by the association of two different uranium polyhedra, pentagonal bipyramids and distorted octahedra. The structure of Rb8U9O31 is built from a regular succession of infinite ribbons similar to those observed in diuranates M2U2O7 (MK, Rb) and infinite three polyhedra wide ribbons , to create an original undulated sheets .For both compounds Rb+ ions occupy the interlayer space and exhibit comparable mobility with conductivity measurements indicating an Arrhenius-type behavior.  相似文献   

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