Les systèmes MFTlF3 (M = Li,Na, K)

A large number of new phases have been prepared and characterized in the MFTlF₃ system: Na₃TlF₆ isostructural with cryolite, Na₃Tl₂F₉, Na_xTl_1−xF_3−2x (0.425 ? x ? 0.565 at 500°C) and Na₅Tl₉F₃₂ related to the fluorite type, K₃TlF₆ with a structure similar to that of (NH₄)₃FeF₆, K₅Tl₃F₁₄ with the chiolite structure, Na_yTl_1−yF_3−2y (0.12 ? y ? 0.14 at 500°C) and K₂Tl₇F₂₃ affiliated to α-UO₃, KTlF₄, and KTl₂F₇.     

121Sb Mössbauer spectra of alkali metal antimonides M3Sb (M3 = Na3, K3, Na2K, Rb3)

¹²¹Sb Mössbauer spectra for M₃Sb (M₃ = Na₃, K₃, Na₂K, Rb₃) were measured at 12 K. The values of isomer shift (d) and quadrupole coupling constant suggest that the valence state of antimony in M₃Sb is –3. The d values increase in the order Rb₃Sb<K₃Sb<Na₃Sb<Na₂KSb. The differences in d values are discussed by examining M–Sb distances and bond valence for M–Sb interactions. Some covalent interactions between alkali metal atoms and antimony atom are suggested.     

Gas-phase chemistry of nitrogen trifluoride NF3: structure and stability of its M–NF3 (M=H, Li, Na, K) complexes

The stationary points characterizing the potential energy profiles of the complex processes of the M⁺(M=H, Li, Na, K) and NF₃ were investigated by QCISD and B3LYP in conjunction with the 6-311+G(2d,2p) basis set. The optimized geometries and NBO analysis indicate that the complexes of M⁺(M=Li, Na, K) and NF₃ exist as ion-dipole molecules. But for H⁺ complexes, there are two stable isomers NF₃H⁺ and NF₂⁺–HF. The interaction distances of isomers follow the sequence H⁺< Li⁺< Na⁺< K⁺. The calculated affinity energies of the most stable isomers of H⁺, Li⁺, Na⁺, and K⁺ complexes exceed 20.1 kJ/mol, and these values suggest that the M⁺–NF₃ (M=H, Li, Na, K) complexes could be observed as stable species in gas phase, which supports Fujii's proposal that Li⁺ ion attachment mass spectrometry can serve as a conceivable technique to quantify the emissions of the NF₃.     

Phase equilibria in M2O-MgO-B2O3 (M=Na, Rb) systems

The Na₂O-MgO-B₂O₃ system (500-550°C) and Rb₂O-MgO-B₂O₃ system (550-700°C) were studied by the methods of powder X-ray diffraction and visual polythermal analysis, and their isothermal sections were constructed at 550 and 650-700°C, respectively. New ternary compounds were found to form: Na₂₄Mg₃B₁₀O₃₀, Na₄Mg₃B₂O₈, and Rb₂Mg₃B₂O₇.     

The crystal chemistry of the M+VO3 (M+ = Li,Na, K,NH4, Tl,Rb, and Cs) pyroxenes

The crystal structures of M⁺VO₃(M⁺ = K, NH₄, and Cs) have been refined using three-dimensional counter-diffractometer X-ray data and full-matrix least-squares methods. The structure of these compounds is characterized by a (V⁵⁺O^2?₃)^?_∞ chain extending along the c-axis (Pbcm orientation), with adjacent chains linked by the alkali metal cation. The structure may be considered as a variant of the pyroxene structure, and standard atom nomenclature is proposed in order to facilitate comparison with silicate pyroxenes. Structural variation across this series is discussed in detail and is compared with the analogous M⁺M³⁺Si₂O₆ (M⁺ = Li, Na; M³⁺ = Al, Cr, Fe, Sc, In) series.     

Crystal structures of M2FeO4 (M = K,Rb, Cs)

The crystal structure of K₂FeO₄, which is isomorphous with β-K₂SO₄, K₂MnO₄ and K₂CrO₄, has been determined in detail. In addition, Rb₂FeO₄ and Cs₂FeO₄ are shown to be of the same structural type. Crystals of K₂FeO₄ are orthorhombic, space group Pnma, a = 7.694(5), b = 5.858(7), c = 10.335(7) with Z = 4. The integrated intensities of 1174 independent reflections were measured with an automated diffractometer and refined to a weighted least-squares residue of 0.046. The average tetrahedral [FeO] bond length, corrected for libration effects, is 1.656(6) Å which is equal within experimental error to values observed for [CrO] and [MnO] tetrahedral bonds.     

Electron spin resonance of diluted solid solutions of Gd2O3 in CeO2

Electron spin resonance spectra of Gd³⁺ in diluted solid solutions of Gd₂O₃ in CeO₂ have been studied at room temperature for Gd concentrations between 0.01 and 1.00 mol%. While in the case of Mn²⁺:CeO₂ samples, both the linewidth and the line intensity go through a maximum between 0.2 and 0.4% Mn and then start to decrease, in the case of Gd³⁺:CeO₂ samples the linewidth and the line intensity increase monotonically with the dopant concentration. This as taken as evidence that in Gd₂O₃-CeO₂ diluted solid solutions there are no clustering effects similar to the ones observed in Mn:CeO₂ solid solutions. It is not clear why clustering effects are present in Mn:CeO₂ solid solutions and not in Gd:CeO₂ solid solutions; however, it seems reasonable to assume that this is due to the fact that the ionic radius of Mn²⁺ (81 pm) is about 25% smaller that that of Gd³⁺ (107.8 pm). In any case, the fact that Gd:CeO₂ solid solutions do not exhibit clustering effects means that ESR linewidth data can be used to estimate the concentration of Gd in CeO₂ samples, as it is possible to do in several solid solutions of paramagnetic ions in ceramic materials. The results also suggest that the range of the exchange interaction between Gd³⁺ ions in CeO₂ is about 0.89 nm.     

New manganites NdM3Sr3Mn4O12 and NdM3Ba3Mn4O12 (M = Li, Na, K): Synthesis and X-ray diffraction characteristics

Manganites NdM₃Sr₃Mn₄O₁₂ and NdM₃Ba₃Mn₄O₁₂ (M = Li, Na, K) were synthesized by a ceramic method from the corresponding oxides and carbonates. The X-ray diffraction analysis showed that all the compounds crystallized in the tetragonal crystal system with the following lattice parameters: NdLi₃Sr₃Mn₄O₁₂: a = 10.88 ?, c = 9.52 ?, V ^o = 1126.9 ?³, Z = 4, ρ_X = 4.95 g/cm³, ρ_pycn = 4.87 ± 0.05 g/cm³; NdNa₃Sr₃Mn₄O₁₂: a = 10.73 ?, c = 10.66 ?, V ^o = 1227.3 ?³, Z = 4, ρ_X = 4.80 g/cm³, ρ_pycn = 4.73 ± 0.07 g/cm³; NdK₃Sr₃Mn₄O₁₂: a = 10.87 ?, c = 11.71 ?, V ^o = 1382.6 ?³, Z = 4, ρ_X = 4.50 g/cm³, ρ_pycn = 4.43 ± 0.09 g/cm³; NdLi₃Ba₃Mn₄O₁₂: a = 10.97 ?, c = 10.34 ?, V ^o = 1244.3 ?³, Z = 4, ρ_X = 5.33 g/cm³, ρ_pycn = 5.23 ± 0.09 g/cm³; NdNa₃Ba₃Mn₄O₁₂: a = 10.99 ?, c = 11.15 ?, V ^o = 1346.7 ?³, Z = 4; ρ_X = 5.11 g/cm³, ρ_pycn = 5.05 ± 0.06 g/cm³; NdK₃Ba₃Mn₄O₁₂: a = 10.997 ?; c = 13.80 ?, V ^o = 1668.9 ?³, Z = 4, ρ_X = 4.32 g/cm³, ρ_pycn = 4.26 ± 0.07 g/cm³. Original Russian Text ? B.K. Kasenov, E.S. Mustafin, M.A. Akubaeva, S.T. Edil’baeva, Sh.B. Kasenova, Zh.I. Sagintaeva, S.Zh. Davrenbekov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 3, pp. 424–427.     

Antiferromagnetism in MUO3 (M=Na,K,Rb) studied by neutron diffraction

Simultaneous refinements of X-ray and neutron powder diffraction patterns taken on the MUO₃ perovskite compounds with M=Na, K and Rb, were performed to reveal anisotropy in the temperature factors, mainly of oxygen. No anisotropic thermal motion was found.The magnetic ordering of the compounds has been investigated with low temperature neutron diffraction. It is found that all these compounds show G-type antiferromagnetic ordering with a similar, orthorhombic magnetic unit cell. The propagation vector could only be determined for the orthorombic NaUO₃ compound and was found to point in the z-direction. The refined magnetic moment for U⁵⁺ in these structures was found to be around .     

Phase formation in the Re-Se-Br-MBr systems (M = Li, Na, K, Rb, Cs)

Phase formation in the Re-Se-Br-MBr systems (M = K, Rb, Cs) was studied by NMR spectroscopy and powder X-ray diffraction. The reactions taking place in alkali metal halide melts were found to give, among the series of cluster anions [{Re₆Se_{8 − n} Br _n }Br₆]^{(4 − n)}− (0 ≤ n≤ 4), polymeric complexes Re₆Se₈Br ₂ and M₂Re₆Se₈Br₄ (M = Cs, Rb) and salts containing cluster anions [Re₆Se₆Br₈]²⁻ and [Re₆Se₇Br₇]³⁻ as the major products. The effect of the alkali metal cation on the product composition and ratio was established. Original Russian Text ? S.S. Yarovoi, Yu.V. Mironov, S.V. Tkachev, V.E. Fyodorov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 2, pp. 344–349.     

19F nuclear magnetic resonance spectra of some trisubstituted metal trifluorophosphine complexes. Examples of [AX3]3 nuclear spin systems

The ¹⁹F NMR spectra of π-allyl-tris(trifluorophosphine)rhodium(I), [A], benzene-tris(trifluorophosphine)chromium(0), [B], and nitrosyl-tris(trifluorophosphine) rhodium(-I), [C], are presented. These are examples of [AX₃]₃ nuclear spin systems (A = phosphorus, X = fluorine). The spectra of [A] and [B] have been completely analysed to afford values of ¹J(PF), ²J(PP′), ³J(PF′) and ⁴J(FF′).     

The lowest triplet state of K2Cr2O7. Electron spin resonance in an external magnetic field at 1.2 K

ESR experiments on the luminescent triplet state of triclinic K₂Cr₂O₇ are reported. For the A site D = 24.300, E = 2.324 GHz, for t     

LiZr4(PO4)3的Na/Li及Ag/Li离子交换

研究了LiZr2(PO4)3在水溶液中的Na/Li和Ag/Li离子交换行为.结果表明,LiZr2(PO4)3对Na+和Ag+离子均具有很高的选择性,且对Ag+的选择性高于Na+.LiZr2(PO4)3与Ag+的离子交换反应是通过形成固溶体的形式进行的,而与Na+的离子交换反应则是通过置换进行的.温度升高有利于提高LiZr2(PO4)3上Na/Li和Ag/Li的离子交换反应速度.     

Electron spin resonance spectra of α-sulfonyl iminoxy radicals

Syn- andanti-α-sulfonyl iminoxy radicals have been generatedin situ by lead tetra-acetate oxidation of α-oximino sulfones. The ESR spectra of the geometrical isomers have been assigned and the¹⁴N and¹H hyperfine splitting constants are discussed in terms of the proposed structures.     

ChemInform Abstract: First‐Principles Investigations of the MMgH3 (M: Li,Na, K,Rb, Cs) Series.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

New alkali-metal-molybdenum(VI)-selenium(IV) oxides: syntheses, structures, and characterization of A2SeMoO6 (A=Na, K, or Rb)

Three new quaternary selenites, A₂SeMoO₆ (A=Na⁺, K⁺, or Rb⁺), were synthesized through the solid-state reaction of A₂MoO₄ with SeO₂ at 400°C. Although the reported materials are ‘stoichiometrically equivalent’, the compounds exhibit strikingly different crystal structures. Whereas Na₂SeMoO₆ has a three-dimensional crystal structure, K₂SeMoO₆ and Rb₂SeMoO₆ are molecular and uni-dimensional, respectively. However, all of the new materials have structures containing Mo⁶⁺ octahedra linked to Se⁴⁺ trigonal pyramids. Although the Mo⁶⁺ and Se⁴⁺ cations are in local asymmetric environments in all three materials, only Na₂SeMoO₆ is non-centrosymmetric. Single crystal X-ray data: Na₂SeMoO₆, cubic, space group, P2₁3 (no. 198), a=8.375(5) Å, Z=4, R(F)=0.0143; K₂SeMoO₆, monoclinic, space group, P2₁/c (no. 14), a=6.118(8) Å, b=15.395(2) Å, c=7.580(9) Å, β=112.39(4)°, Z=4, R(F)=0.0281; Rb₂SeMoO₆, orthorhombic, space group, Pnma (no. 62), a=7.805(9) Å, b=6.188(7) Å, c=14.405(4) Å, Z=4, R(F)=0.0443.     

Synthesis,mass spectra,raman and infrared spectra of the compounds M(PF3)6 (M = Cr,Mo, W)

An improved method of synthesis of hexakis(trifluorophosphine)chromium(0), -molybdenum(0)and -tungsten(0) is described, involving photochemically induced substituion of carbonyl groups from the (trifluorophosphine)tricarbonylmetallates by PF₃ under moderate pressure. A full analysis of the fragmentation patterns in a mass spectrometer is given, and both Raman and infrared data obtained throughoutthe range 4000–50 cm^?1 are discussed. Complete vibrational mode assignments are made, and a normal coordinate analysis leading to the determination of force constants and potential energy distributions is presented. The normal mode in which M-P bond stretching is predominant in all cases involves a significant contribution from PF bond stretching in these molecules.     

Structural phase stability studies on MBeH3 (M = Li, Na, K, Rb, Cs) from density functional calculations

Density functional theory calculations within the generalized-gradient approximation are used to establish the ground-state structure, equilibrium structural parameters, and electronic structure for MBeH(3) phases. From the 24 structural arrangements used as inputs for structural optimization calculations, the ground-state crystal structures of MBeH(3) phases have been predicted. At ambient conditions, LiBeH(3) and NaBeH(3) crystallize with perovskite-related orthorhombic and cubic structures, respectively. The remaining phases KBeH(3), RbBeH(3), and CsBeH(3) crystalize in a monoclinic structure. In the predicted phases one can store up to 15.93 wt % of hydrogen. The formation energy for the MBeH(3) phases have been investigated along different reaction pathways. The electronic structures reveal that all these phases are insulators with estimated band gaps varying between 1.79 and 3.44 eV.     

Vibrational spectra and structure of AlCl3NH3 and molten mixtures with MCl-AlCl3 (M = Li,Na, K OR Cs)

Raman and IR spectra were obtained of molten AlCl₃NH₃, AlCl₃ND₃ and AlBr₃NH₃ in addition to chloroaluminate mixtures of the AlCl₃NH₃. The main spectral features of the gaseous AlCl₃NH₃ molecules having a C_3v-symmetry are retained in the molten and glassy states. Some additional bands were observed both in the pure liquid and in mixtures with chloroaluminate melts. The spectra indicated that the discussion reaction 2AlCl₃NH₃ = AlCl⁻₄ + [AlCl₂(NH₃)₂]⁺ occurs with K ⋍ 3 × 10⁻³ (mole fraction basis). Frequency shifts found on liquefaction demonstrate that extensive hydrogen bonding takes place between AlCl₃NH₃ molecules. This observation is supported by the glass-forming nature of AlCl₃NH₃. The molecule Al₂Cl₆NH₃ seems to exist in binary AlCl₃-AlCl₃NH₃ melts.     

Synthesis and crystal structure of new uranyl tungstates M2(UO2)(W2O8) (M=Na, K), M2(UO2)2(WO5)O (M=K, Rb), and Na10(UO2)8(W5O20)O8

The solid-state reactions of UO₃ and WO₃ with M₂CO₃ (M=Na, K, Rb) at 650°C for 5 days result, accordingly the starting stoichiometry, in the formation of M₂(UO₂)(W₂O₈) (M=Na (1), K (2)), M₂(UO₂)₂(WO₅)O (M=K (3), Rb (4)), and Na₁₀(UO₂)₈(W₅O₂₀)O₈ (5). The crystal structures of compounds 2, 3, 4, and 5 have been determined by single-crystal X-ray diffraction using Mo(Kα) radiation and a charge-coupled device detector. The crystal structures were solved by direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F² for all unique reflections. For (1), unit-cell parameters were determined from powder X-ray diffraction data. Crystallographic data: 1, monoclinic, a=12.736(4) Å, b=7.531(3) Å, c=8.493(3) Å, β=93.96(2)°, ρ_cal=6.62(2) g/cm³, ρ_mes=6.64(1) g/cm³, Z=4; 2, orthorhombic, space group Pmcn, a=7.5884(16) Å, b=8.6157(18) Å, c=13.946(3) Å, ρ_cal=6.15(2) g/cm³, ρ_mes=6.22(1) g/cm³, Z=8, R1=0.029 for 80 parameters with 1069 independent reflections; 3, monoclinic, space group P2₁/n, a=8.083(4) Å, b=28.724(5) Å, c=9.012(4) Å, β=102.14(1)°, ρ_cal=5.83(2) g/cm³, ρ_mes=5.90(2) g/cm³, Z=8, R1=0.037 for 171 parameters with 1471 reflections; 4, monoclinic, space group P2₁/n, a=8.234(1) Å, b=28.740(3) Å, c=9.378(1) Å, β=104.59(1)°, ρ_cal=6.13(2) g/cm³,  g/cm³, Z=8, R1=0.037 for 171 parameters with 1452 reflections; 5, monoclinic, space group C2/c, a=24.359(5) Å, b=23.506(5) Å, c=6.8068(14) Å, β=94.85(3)°, ρ_cal=6.42(2) g/cm³,  g/cm³, Z=8, R1=0.036 for 306 parameters with 5190 independent reflections. The crystal structure of 2 contains linear one-dimensional chains formed from edge-sharing UO₇ pentagonal bipyramids connected by two octahedra wide (W₂O₈) ribbons formed from two edge-sharing WO₆ octahedra connected together by corners. This arrangement leads to [UW₂O₁₀]²⁻ corrugated layers parallel to (001). Owing to the unit-cell parameters, compound 1 probably contains similar sheets parallel to (100). Compounds 3 and 4 are isostructural and the structure consists of bi-dimensional networks built from the edge- and corner-sharing UO₇ pentagonal bipyramids. This arrangement creates square sites occupied by W atoms, a fifth oxygen atom completes the coordination of W atoms to form WO₅ distorted square pyramids. The interspaces between the resulting [U₂WO₁₀]²⁻ layers parallel to plane are occupied by K or Rb atoms. The crystal structure of compound 5 is particularly original. It is based upon layers formed from UO₇ pentagonal bipyramids and two edge-shared octahedra units, W₂O₁₀, by the sharing of edges and corners. Two successive layers stacked along the [100] direction are pillared by WO₄ tetrahedra resulting in sheets of double layers. The sheets are separated by Na⁺ ions. The other Na⁺ ions occupy the rectangular tunnels created within the sheets. In fact complex anions W₅O₂₀¹⁰⁻ are built by the sharing of the four corners of a WO₄ tetrahedron with two W₂O₁₀ dimmers, so, the formula of compound 5 can be written Na₁₀(UO₂)₈(W₅O₂₀)O₈.