Crystal growth, characterization and physical properties of PrNiSb3, NdNiSb3 and SmNiSb3

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 μ_B, 3.90 μ_B and 0.80 μ_B are found for PrNiSb₃, NdNiSb₃ and SmNiSb₃, respectively, and are consistent with Pr³⁺ (f ²), Nd³⁺ (f ³), and Sm³⁺ (f ⁴).     

PbI4Cu2(PPh3)4: A heterometallic iodide with unusual cis-divacant octahedral coordination sphere for lead: Synthesis, structure, red-infrared fluorescence and theoretical studies

A new heterometallic iodide, PbI₄Cu₂(PPh₃)₄, was synthesized by reactions of PbI₂, CuI and triphenylphosphine (PPh₃) in DMF solution. The single-crystal X-ray diffraction analyses show that Pb(II) center adopts an unusual cis-divacant octahedral geometry. Crystal data: triclinic, space group , , , , α=106.623(4)°, β=103.478(6)°, γ=93.574(5)°, and Z=2. Density function theory (DFT) calculations and fragment orbital interaction analyses reveal the presence of a three-center four-electron (3c-4e) hypervalent bonding about lead; and the formation of the unusual cis-divacant [PbI₄]²⁻ octahedron is energetically favorable. The title yellow compound has an optical bandgap of 2.69 eV and shows remarkable red-infrared fluorescence emission at 732 nm with lifetime of 24 μs which is assigned as an iodine 5p-lead 6s to PPh₃-lead 6p charge transfer (XM-LM-CT).     

Thermodynamic studies on the interactions of diglycine with magnesium chloride in aqueous medium at different temperatures

Apparent molar heat capacities (C_P2,?), apparent molar volumes (V_2,?), and viscosities (η) of diglycine in water and in aqueous magnesium chloride (MgCl₂) solutions of molality m_S ≈ (0.05 to 0.70) mol · kg⁻¹ over the temperature range T = (288.15 to 328.15) K have been determined using high sensitivity micro-differential scanning calorimeter, vibrating-tube digital density meter, and automatic viscosity measuring unit (AVS 350), respectively. The data have been used to calculate the partial molar heat capacities and partial molar volumes at infinite dilution. The viscosity B-coefficients have also been obtained from viscosity data using Jones-Dole equation. The and values of diglycine in aqueous MgCl₂ solutions are higher than those in water and thus exhibit positive transfer functions ( and ), which are indicative of strong interactions between diglycine and MgCl₂. Corresponding viscosity B-coefficients of transfer are also generally positive. The transfer functions decrease with increase in temperature and increase with the concentration of MgCl₂. The free energies, enthalpies and entropies of activation for viscous flow of diglycine in aqueous MgCl₂ solutions have been obtained by using the Feakins transition-state theory. Partial molar expansibilities and at infinite dilution along with their temperature dependence, the interaction coefficients from the volume, heat capacity, and viscosity B-coefficients have been used to divulge the various kinds of plausible interactions between solute (diglycine) and cosolute (MgCl₂) in solutions.     

Synthesis of N-alkylimidazolium salts and their utility as solvents in the Beckmann rearrangement

Six different room temperature ionic liquids (RTILs) based on N-methyl or N-isopropyl imidazolium cations with counteranions, such as , , and OTf⁻, have been synthesized by exchanging the counteranions of the corresponding N-methyl or N-isopropylimidazolium bromides using appropriate salts such as NH₄BF₄, KPF₆, and AgOTf. Catalytic amounts of these ionic liquids (ILs) have been used as the reaction medium for the Beckmann rearrangement of oximes to amides in the presence of PCl₅. A moderate to good conversion of oximes to amides in all the six ILs was observed.     

Structural and conductivity studies of CsKSO4Te(OH)6 and Rb1.25K0.75SO4Te(OH)6 materials

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. Rb_1.25K_0.75SO₄Te(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^*=Z^′—iZ^″) 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^*.     

Crystal structure and vibrational properties of new luminescent hosts K3YF6 and K3GdF6

The luminescence hosts K₃YF₆ and K₃GdF₆ were obtained in a single-crystal form. Their crystal structure was determined from single-crystal X-ray diffraction data. Both crystals adopt monoclinic system with space group P2₁/n, Z=2. Lattice parameters for K₃YF₆ are refined to the following values , , , β=90.65(3) and for K₃GdF₆, , , β=90.80(3). The vibrational analysis, IR and Raman spectroscopy at room temperature, was applied to these compounds in order to study the site symmetry of Y³⁺ and Gd³⁺ ions.     

Structural evolution in iron tellurates

Three new members within the iron tellurate family have been synthesized and characterized by single-crystal diffraction. Fe₂Te₃O₉ is orthorhombic, , , , Z=4, space group Pnma, final agreement factors R₁=0.0261(wR₂=0.0688) for 1271 independent reflections. Fe₃Te₄O₁₂ is monoclinic, , , , β=107.950(10)^°, Z=4, space group P2₁/c, final agreement factors R₁=0.0380(wR₂=0.0281) for 3302 independent reflections. FeTe₆O₁₃ is trigonal, , , Z=6, space group , final agreement factors R₁=0.0309(wR₂=0.0641) for 1264 independent reflections. Together with the four already known members of the family, Fe₂TeO₅, Fe₂TeO₆, and Fe₂Te₃O₉ (a dimorphic variant of the afore-mentioned structure with the same chemical formula), and Fe₂Te₄O₁₁, the iron tellurates now span from relatively Fe-rich and Te-poor to relatively Fe-poor to Te-rich compounds. The structural diversity within Fe-Te-O system is discussed in terms of the lone-pair stereochemistry of the Te⁴⁺ anion and the cross-over from Fe³⁺ to mixed-valence Fe³⁺/Fe²⁺ and Fe²⁺ coordination polyhedra compounds.     

Three-dimensional framework of uranium-centered polyhedra with non-intersecting channels in the uranyl oxy-vanadates A2(UO2)3(VO4)2O (A=Li, Na)

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, ρ_mes=5.32(2) g/cm³, ρ_cal=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).     

Synthesis and crystal structures of La3MgBi5 and LaLiBi2

Two new ternary bismuthides, La₃MgBi₅ and LaLiBi₂, have been prepared by solid-state reactions of the corresponding pure metals in welded niobium tubes at high temperature. Their structures have been established by single-crystal X-ray diffraction studies. La₃MgBi₅ crystallizes in the hexagonal space group P6₃/mcm (No.193) with cell parameters of , , , and Z=2. LaLiBi₂ belongs to tetragonal space group P4/nmm (No.129) with cell parameters of , ,, and Z=2. The structure of La₃MgBi₅ is of the ‘‘anti’’ Hf₅Sn₃Cu type, and features 1D linear Bi⁻ anionic chains and face-sharing [MgBi_6/2]⁷⁻ octahedral chains. The structure of LaLiBi₂ is isotypic with HfCuSi₂, and is composed of 2D Bi⁻ square sheets and 2D LiBi layers with La³⁺ ions as spacers. Band calculations indicate that both compounds are metallic.     

Photoluminescent behavior of SrB4O7:RE (RE=Sm and Eu) prepared by Pechini, combustion and ceramic methods

This work reports the preparation of system containing RE²⁺ ions (RE=Sm and Eu)-doped in SrB₄O₇ matrix by ceramic, Pechini and combustion methods. These compounds were prepared by reduction of RE³⁺ to RE²⁺ in air, which exhibit some different features according to the preparation method. Photoluminescent properties of these systems were investigated based on the emission and excitation spectral data. The emission spectra of SrB₄O₇:Eu²⁺ system prepared by combustion and Pechini methods are characterized by a broad band assigned to interconfigurational 4f⁶5d→4f⁷ transition, while SrB₄O₇:Sm²⁺ compound exhibit narrow emission bands arising from intraconfigurational-4f⁶ also shows ⁴G_5/2→⁶H_J′ transitions ( and ) arising from Sm³⁺ ion, transitions. SrB₄O₇:RE system prepared by combustion method presents emission bands from RE³⁺ ions as intense as that arising from RE²⁺, suggesting that the preparation route is not efficient for the reduction RE³⁺→RE²⁺ process. Emission quantum efficiency and radiative emission rates of Sm²⁺ ion are determined and discussed.     

Crystal structures of Rb2U2O7 and Rb8U9O31, a new layered rubidium uranate

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.     

Silver-halide/organic-composite structures: Toward materials with multiple photographic functionalities

We report the synthesis and structure of the novel silver-halide-based organic-inorganic hybrids Ag₂Br₆(PPD)₂, Ag₂Br₆(CD-2)₂·H₂O, Ag₂Br₄(TMBD), and Ag₂I₆(CD-2)₂·H₂O. 1,4-phenylenediammonium hexabromodiargentate(I) [Ag₂Br₆(PPD)₂] crystals are monoclinic (P2₁/n), with unit-cell dimensions, , , and β=93.109(1)°. N,N-diethyl-2-methyl-1,4-benzenediammonium hexabromodiargentate(I) monohydrate [Ag₂Br₆(CD-2)₂·H₂O] crystals are monoclinic (space group P2₁/c) with , , , and β=96.153(1)°. N,N,N′,N′-tetramethyl-1,4-benzenediammonium tetrabromodiargentate(I) [Ag₂Br₄(TMBD)] crystals are orthorhombic (space group Pbcn) with , , and . N,N-diethyl-2-methyl-1,4-benzenediammonium hexaiododiargentate(I) monohydrate, [Ag₂I₆(CD-2)₂·H₂O], are monoclinic (C2/c), with unit-cell dimensions, , , , and β=98.657(1)°. The novel structures are members of a class of silver-halide-based organic-inorganic hybrids based upon the assembly of [Ag_aX_b]ⁿ⁻ clusters and protonated organoamines in aqueous mineral acids. The clusters display short intracluster Ag-Ag distances, and computational methods are used to evaluate intracluster Ag-Ag bonding. The diverse stoichiometries and cluster connectivities observed suggest a rich compositional and structural chemistry based upon the general assembly method. We have extended the methodology to include a silver-halide-organoamonium chemistry in which the organic moiety is chosen to serve a specific photographic function and demonstrate the first examples of such materials. The methodology allows for the direct assembly of [Ag_aX_b]ⁿ⁻ clusters with commercial photographic color developer molecules, and we show that development is repressed but can later be “switched on” in a unique photographic scheme. The photographic properties of Ag₂Br₆(PPD)₂ are examined and show an extremely facile development rate owing to the fact that the developer molecules are within molecular proximity to the clusters. As a result of their molecular nature, we anticipate that such materials could enable conventional or completely new imaging technologies with very fast image access rates and very high resolution.     

Synthesis and magnetic properties of the quasi-one-dimensional compound Ca0.83(Cu1−xCox)O2

A new solid solution of the quasi-one-dimensional composite crystal, , has been synthesized under of O₂ at 830°C. The non-doped compound Ca_0.83CuO₂ consists of two interpenetrating monoclinic subsystems of the [Ca] atoms and the edge-shared square planar [CuO₂] chains. Upon increasing x, both the subsystems undergo a phase change from monoclinic to orthorhombic (M-O). The M-O change occurs at x∼0.04 for the [(Cu,Co)O₂] subsystem, while such a change occurs at x∼0.17 for the [Ca] subsystem. Magnetic susceptibility measurements show an evolution from a short-range ordered state near x=0 to a long-range antiferromagnetic state for the samples with x?0.15. The effective magnetic moment μ_eff is found to increase with increasing x from for x=0.10 to for x=0.30, suggesting that the solid solution can be regarded as Ca_0.83[Cu_0.66²⁺Cu_0.34−x³⁺Co_x³⁺]O₂, in which a mixed state of Cu²⁺(S=1/2), Cu³⁺(S=0) and high-spin Co³⁺(S=2) ions is realized.     

Syntheses and crystal structures of two new pentaborates

Two new pentaborates, [Zn(DIEN)₂][B₅O₆(OH)₄]₂ (DIEN=diethylenetriamine) (I) and [B₅O₇(OH)₃Zn(TREN)] (TREN=tris(2-aminoethyl)amine) (II), have been hydrothermally synthesized and characterized by single crystal X-ray diffraction, FTIR, elemental analysis and thermogravimetric analysis. Compound I crystallizes in the monoclinic system, space group P2₁/c (No. 14), , , , β=91.259(2)°, , Z=2. The structure consists of isolated borate polyanion [B₅O₆(OH)₄]⁻ and zinc complex cation [Zn(DIEN)₂]²⁺. The anionic units, [B₅O₆(OH)₄]⁻, are linked by hydrogen bonds to form a 3D supramolecular network containing large channels, in which the templating [Zn(DIEN)₂]²⁺ cation are located. II is monoclinic, P2₁/c (No. 14), , , , β=99.635(2)°, , Z=4. The structure of II is constructed from two distinct motifs, a usual [B₅O₇(OH)₃]²⁻ cluster and a supporting zinc complex [Zn(TREN)]²⁺, which are integrated through Zn-O-B linkage. This compound represents the first example of the combination of B-O cluster with transition-metal complex.