The defect solid solution Na7/8(Fe7/8+xTi9/8−2xSbx)O4 (0 ≤ x ≤ 1/3): Evidence of Na mobility in the tunnels of a quadruple rutile-chain structure

A new defect solid solution, the series Na_7/8(Fe^III_7/8+xTi^IV_9/8−2xSb^V_x)O₄, was synthesized. Its homogeneity range is rather wide: 0 <- x ≤ 0.33. The incorporation of Sb^V gives rise to a progressive increase of the parameters of the orthorhombic unit cell. X-ray powder structure calculations point to a partial occupancy of the large double tunnels in a quadruple rutile-chain structure. A significant ordering of cations over the octahedral framework is observed, owing to a Ti^IV---Sb^V segregation. Electrical measurements emphasize a cationic conductivity, mainly related to a 1D motion of Na^I cations. A transition from a low activation energy process—E_A ≤ 0.20 eV—to a high activation energy one—E_A ≈ 0.75 eV—systematically occurs at T ≈ 440°C, independent of the Sb^V concentration. A possible skew motion from a half tunnel to another one is proposed as a tentative explanation of the high-temperature conductivity mechanism.     

Preparation and characterization of a novel hybrid magnetic semiconductor containing rare, one-dimensional mixed-iodide/chloride anion of lead(II)

A new hybrid inorganic–organic magnetic semiconductor [Ni(bipy)₃Pb₂I_4.84Cl_1.16·DMF]_n (bipy=2,2′-bipyridine) containing novel one-dimensional mixed-halide anion of lead(II) was synthesized by reactions of PbI₂, NaI, NiCl₂ and bipy in DMF solution, and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the space group C2/c with a=29.260(8) Å, b=15.602(4) Å, c=23.695(6) Å, β=126.815(°), Z=8, V=8660(4) Å³ and consists of a magnetic cation [Ni(bipy)₃]²⁺ in addition to one-dimensional mixed-halide anion, which is built up of face-sharing [PbX₆] octahedra. Of the seven crystallographically independent halide sites in this anion, one and five are occupied by Cl and I, respectively, the remaining one has mixed-iodide and -chloride occupancy. The title yellow compound has an optical bandgap of 2.59 eV, and the variable-temperature magnetic susceptibility measurement indicates paramagnetic behavior.     

On the conformation of 6-ketononanolide and 1,4-cyclohexanedione in solution by dipole moment studies

The dipole moments of 6-ketononanolide (1) and its 2,4,7 and 8-Me derivatives (2–5) are found to be 1·8 – 1·9±0·2 D. Utilizing the known solid-state geometry of 1, a dipole moment of 1·6 D is calculated by the INDO quantum mechanical method. Thus the conformation of 1 in solution does not differ much from its solid-state conformation which is diamond-lattice derived with the CO groups 174° apart and in “Type III” positions. However, the IR spectrum of 1 in solution shows differences from that in the solid state (Nujol or KBr).The dipole moment of 1,4-cyclohexanedione (10) is calculated to be 1·2 D for the experimental 156° twist boat conformation (found in the solid-state). This is in excellent agreement with the experimental value found by several groups. 1,6-Cyclodecanedione (6), however, is found to have an experimental dipole moment of 0·7 D, as contrasted with a calculated value of 0 D for 180° opposed carbonyls.     

Mössbauer study of the FeV2O4---Fe3O4 system

Mössbauer spectra of the Fe_1+xV_2−xO₄ spinel solid solutions are taken to investigate the cation distribution. Room temperature spectra can be interpreted by assuming that the cation distribution is represented approximately as Fe²⁺[Fe³⁺_xV³⁺_2−x]O₄ for 0 x 0.35 and Fe³⁺[Fe²⁺Fe³⁺_x−1V³⁺_2−x]O₄ for 1 x 2 and the ionic valence arrangement changes from the 2-3-3 type (Fe²⁺[Fe³⁺_xV³⁺_2−x]O₄) to the 3-2-3 one (Fe³⁺[Fe²⁺V³⁺]O₄) in the range 0.35 x 1. Fe₂VO₄ is found to be 3-2-3 spinel, Fe³⁺[Fe²⁺V³⁺]O₄. Its paramagnetic spectrum at 473°K is, however, composed of a broad single line with isomer shift value of 0.61 mm/sec relative to stainless steel, in which the line splitting due to the ferric and ferrous ions is rendered indistinguishable.     

Heteropoly Complexes Na0.5Cs2 ? x[H0.5 ? xM

Crystals of novel heterepoly complexes (HPC) Na_0.5Cs_{2 − x} [H_{0.5 − x} M _x ^II X^III(OH)₆Mo₆O₁₈] · 7−8H₂O (M^II = Fe, Mn; X^III = Cr, Al) are synthesized. Crystal structures of the complexes Na_0.5Cs_{2 − x} [H_{0.5 − x} Fe_xCr(OH)₆Mo₆O₁₈] · 7H₂O (I) (x = 0.19) and Na_0.5Cs_{2 − x} [H_{0.5 − x} Mn_xAl(OH)₆Mo₆O₁₈] · 8H₂O (II) (x = 0.22) are determined (space group Pbcn, Z = 8, a = 23.023(4) Å, b = 22.064(4) Å, c = 11.606(3) Å, V = 5895.66 ų for I and a = 22.972(9) Å, b = 22.002(8) Å, c = 11.543(5) Å, V = 5834.18 ų for II, respectively). The [X^III(OH)₆Mo₆O₁₈]³⁻ ligands were found to be coordinated in monodentate fashion to M atoms due to the participation of a terminal O atom of the cis-MoO₂ group in coordination with the Fe and Mn atoms, which was confirmed by IR data. __________ Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 9, 2005, pp. 663–676. Original Russian Text Copyright ? 2005 by Gavrilova, Molchanov.     

Synthesis and electrochemical properties of Li9V3 − x Ti x (P2O7)3(PO4)2/C compounds via wet method for lithium-ion batteries

A series of Ti⁴⁺-doped Li₉V_3???x Ti _x (P₂O₇)₃(PO₄)₂/C compounds have been prepared by using wet method. X-ray diffraction measurement shows that single phase region can be expressed as x?≤?0.10. The effects of substitution of Ti for V on the electrochemical properties of Li₉V_3???x Ti _x (P₂O₇)₃(PO₄)₂ compounds have been studied. Our investigations show that Ti doping can improve the electrochemical performance. The Li₉V_2.95Ti_0.05(P₂O₇)₃(PO₄)₂/C exhibits the best cycle performance and the highest first discharge capacity of 120.7 mAh g^?1 at 0.2 C. The electrochemical impedance spectroscopy indicates that the charge transfer resistance initially decreases with x and then for x?>?0.05 increases monotonically with Ti⁴⁺ content.     

Preparation and characterization of spherical V2O3 nanopowder

V₂O₃ nanopowder with spherical particles was prepared by reducing pyrolysis of the precursor, (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O, in H₂ atmosphere. The thermolysis process of the precursor in a H₂ flow was investigated by thermogravimetric analysis and differential thermal analysis. The results indicate that pure V₂O₃ forms at 620°C and crystallizes at 730°C. The effects of various reductive pyrolysis conditions on compositions of V₂O₃ products were studied. Scanning electron micrographs show that the particles of the V₂O₃ powder obtained at 650°C for 1 h are spherical about 30 nm in size with more homogeneous distribution. Experiments show that nanopowder has larger adsorption capacity to gases and is more easily reoxidized by air at room temperature than micropowder. Differential scanning calorimetry experiment indicates that the temperature of phase transition of nano-V₂O₃ powder is −119.5°C on cooling or −99.2°C on heating. The transition heats are −12.55 J g⁻¹ on cooling and 11.42 J g⁻¹ on heating, respectively.     

Computer automation of polarographic analyzer PAR 384B and development of specific implementation software

The automation of Polarographic Analyzer PAR 384B by connecting it to an HP 9816S Technical Computer is presented. The connection itself transforms an analytically oriented instrument towards one which is more appropriate for research work. Specific implementation software is developed in order to enable and facilitate pseudopolarographic measurements and evaluation of heavy-metal complexation phenomena. As as example, the procedure for the simultaneous determination of the stability constants of lead and cadmium present in constant ionic strength medium of X mol/dm³ NaCl + (4 − X) mol/dm³ NaClO₄ is presented. The results obtained, for lead, β₁ = 9±1, β₂ = 92±13, β₃ = 99±21, β₄ = 27±6, and for cadmium, β₁ = 44±3, β₂ = 194±36, β₃ = 816±67, β₄ = 68±24, are in agreement with the literature data.     

n-Butane Oxidation over γ-Al2O3 Supported Vanadium Phosphate Catalysts

Four vanadium phosphate catalysts supported onγ-Al_2O_3(20 wt%)were synthesized via wetness impregnation of VOHPO_4·0.5H_2O precursor and calcined for different durations(6,10,30 and 75 h)at 673 K in a reaction flow of n-butane/air mixture.The samples calcined for 6 and 10 h produced only a single phase of(VO)_2P_2O_7.However,the VOPO_4 phase(β-VOPO_4)was detected and became more prominent with only a minor pyrophosphate peaks were found after 30 h of calcination.All these pyrophosphate peaks disappeared after 75 h of calcination.The formation of V~(5 )phase was also observed in the SEM micrographs.The redox properties and the nature of oxidants of the catalysts employed in this study were investigated by H_2-TPR analysis.Selective oxidation of n-butane to maleic anhydride(MA) over these catalysts shows that the percentage of n-butane conversion decreases with the transformation of the catalysts from V~(4 )to V~(5 )phases.An appropriate ratio of V~(5 )/V~(4 )can enhance the performance of the VPO catalyst.However,a higher amount of V~(5 )and its associated oxygen species are responsible to promote the MA selectivity.     

Studies of organotin(IV)-orthoquinone systems

The primary process in the reaction of hexaphenylditin with various substituted orthoquinones (Q) is shown to involve attack by the quinone at a phenyl ligand. The intermediate thus formed decomposes to yield Ph₃Sn(SQ^·), where S(Q^·−) is the corresponding semiquinonate. Rearrangement of these species in solution gives rise to biradicals, while intramolecular electron transfer may lead to the formation and precipitation of Ph₂Sn(CAT), where CAT²⁻ is the corresponding substituted catecholate. The identification of these processes depends in part on electron paramagnetic resonance spectroscopy. The reaction of Ph₃SnCl or Ph₂SnCl₂ with Na(TBSQ^·) (TBSQ^·−=3,5-di-tert-butyl-orthobenzosemiquinonate) results in the formation of Ph₂Sn(TBSQ^·), which can undergo redistribution and intramolecular electron transfer, so that the solution chemistry of these latter systems is similar to that of the products of the Sn₂Ph₆+Q reaction.     

Structural studies in main group chemistry : XIX. Organotin(IV) derivatives of tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane and 2,3,5,6-tetrachlorobenzoquinone. The isolation of stable organotin-substituted radicals

The reaction of organotin chlorides with the lithium salt of 7,7,8,8-tetracyanoquinodimethane (TCNQ) or hexaalkylditins with TCNQ yield stable organotin-substituted free radicals of the types R₃SnTCNQ^. (R = Me, n-Pr, n-Bu) and Me₂Sn(TCNQ^.)₂. The reaction of hexaphenylditin with TCNQ yields a (σ → π) charge transfer complex of stoichiometry (Ph₃SnSnPh₃)·TCNQ, whilst [Me₂SnCl(terpyridyl)⁺](TCNQ^-·) was isolated from the reaction of [Me₂SnCl(terpyridlyl)⁺][Me₂SnCl₃^-] and LiTCNQ. The oxidation of hexaalkylditins by tetracyanoethylene (TCNE) yields stable free radicals of the type R₃SnTCNE·, but treatment with 2,3,5,6-tetrachlorobenzoquinone yields either R₃SnOC₆Cl₄O·-p (R = Me) or R₃SnOC₆Cl₄OSnR₃-p (R = n-Bu, Ph). Tin-119 Mössbauer spectroscopy shows that the derivatives R₃SnTCNQ· and R₃TCNE· have trigonally-bipyramidally coordinated tin with planar [SnC₃] skeletons and bridging [TCNQ·] and [TCNE·] groups forming infinite one-dimensional chain structures. Me₃SnOC₆Cl₄O·-p was inferred to possess a similar structure but with oxy bridges forming chains with a Sn---O---Sn---O backbone. Me₂Sn(TCNQ·)₂ has a structure intermediate between tetrahedral and octahedral with a non-linear MeSnMe unit and anisobidentate chelation by two TCNQ groups. The TCNQ derivatives were of two types: (i) “green” or “brown”, indicative of delocalisation of the Ione electron over the cyanoquinone ligand, and (ii) a “blue” form in which spin-pairing of the Ione electron between adjacent organic groups takes place. Me₃SnTCNQ· may exist in both forms depending upon the mode of preparation.     

Cobalt-thioalkylazoimidazole complexes: Structures, spectra and redox properties

1-Alkyl-2-{(o-thioalkyl)phenylazo}imidazole (SRaaiNR^/, 1) reacts with Co(ClO₄)₂·6H₂O to form [Co(SRaaiNR^/)₂](ClO₄)₂ (2). The single crystal X-ray structure of one of the complexes of 2 shows a tridentate chelation N(imidazole), N(azo), S(thioether) system. In the structure one of ClO₄⁻ anions shows disorder and forms an (imidazole)C–H···O(ClO₃) interaction leading to a 1-D chain. Co(OAc)₂.4H₂O and SRaaiNR^/ react in the presence of NH₄SCN (1:1:2 mole ratio) in methanol and the complex [Co(SRaaiNR^/)₂(SCN)₂] (3) has been separated. The single crystal X-ray structure determination has established the structure of the complexes in which the ligand SRaaiNR^/ acts in a bidentate N(imidazole), N(azo) chelation mode. A cyclic voltammogram shows a Co(III)/Co(II) oxidative response at 0.6–0.8 V and azo reductions. DFT computation using optimized geometry support the electronic spectral and redox properties of the complexes.     

Coordination networks constructed with supramolecular synthon RX–CCAgn (n = 4, 5; RX = halophenyl)

Eight new silver(I) double salts: AgL¹·2AgCF₃COO (1), AgL¹·3AgNO₃ (2), 2AgL²·5AgCF₃COO·2CH₃CN·H₂O (3), 4AgL³·6AgCF₃COO·5CH₃CN (4), 4AgL⁴·6AgCF₃COO·5CH₃CN (5), 2AgL⁵·4AgCF₃COO·NC(CH₂)₄CN (6), 2AgL⁵·4AgCF₃COO·2CH₃CN (7) and AgL⁶·2CF₂(CF₂COOAg)₂·2CH₃CN (8) (L¹ = 4-iodophenylethynide; L² = 3,4-dichlorophenylethynide; L³ = 3-chlorophenylethynide; L⁴ = 3-bromophenylethynide; L⁵ = 2-chlorophenylethynide; L⁶ = 2-fluorophenylethynide) have been synthesised and characterized by X-ray crystallography. All compounds contain the silver–halophenylethynide supramolecular synthon R_X−CCAg_n (n = 4, 5). In particular, the three-dimensional supramolecular structures in 1 and 2 are stabilized by strong AgI interactions, while that in 3 is consolidated by both AgCl and van der Waals type FCl interactions. In isomorphous compounds 4 and 5, the presence of respective FCl or FBr contact contributes to the stability of the network. The silver aggregates in 6, 7 and 8 are stabilized by AgCl or AgF interactions between the ortho-halo substituent and the Ag_n basket.     

Excess Molar Volumes and Excess Logarithm Viscosities for Binary Mixtures of the Ionic Liquid 1-Butyl-3-methylimidazolium Hexaflurophosphate with Some Organic Compounds

Experimental data of densities and viscosities are presented for the mixtures of the ionic liquid 1-butyl-3-methylimidazolium hexaflurophosphate, [C₄mim][PF₆], with acetone, 2-butanone, 3-pentanone, cyclopentanone and ethyl acetate at 298.15 K. Based on these data, excess molar volumes, V_m^E, and excess logarithm viscosities, (lnη)^E, have been determined for the binaries. It is shown that all values of V_m^E are negative but those of (lnη)^E are positive. Interestingly, a minimum in V_m^E and a maximum in (lnη)^E are observed at about the same mole fraction of the ionic liquid (x = 0.3) for every mixture investigated. Combined with the V_m^E data reported in literature, the effects of the [PF₆]⁻ and [BF₄]⁻ anions are compared. The results have been discussed in terms of the ion–dipole interactions of the cations of the ionic liquids with the organic compounds as well as their influence on the association of [C₄mim]⁺ and [PF₆]⁻ in the ionic liquid.     

Mouvement du lithium dans deux nouvelles familles d'électrolytes solides: Les boracites Li4+xB7O12+x/2Cl et les halogénoborates de lithium vitreux

The boracites Li_4+xB₇O_12+x/2Cl and the related B₂O₃---xLi₂O---yLiCl glasses have been studied by cw and pulsed NMR between 130 and 500°K. Above 160°K the ⁷Li spectrum is composed of two lines: a broad one due to nonmobile Li⁺ ions and a narrow one due to diffusing Li⁺ with a hopping frequency greater than the dipolar frequency. The activation energy deduced from spin-lattice relaxation time measurements (T₁) is lower than that given by variation of conductivity with temperature. At low temperature T₁ disagrees with the BPP prediction (T₁ ω²_o). The diffusion process may be explained by the existence of a distribution of the local energy barriers.     

X-Ray Diffraction Study of Cs5(HSO4)3(H2PO4)2, a New Solid Acid with a Unique Hydrogen-Bond Network

Solid solution investigations in the CsHSO₄–CsH₂PO₄system, carried out as part of an ongoing effort to elucidate the relationship between proton conduction, hydrogen bonding, and phase transitions, yielded the new compound Cs₅(HSO₄)₃(H₂PO₄)₂. Single-crystal X-ray diffraction methods revealed that Cs₅(HSO₄)₃(H₂PO₄)₂crystallizes in space groupC2/c(or possiblyCc), has lattice parametersa=34.066(19) Å,b=7.661(4) Å,c=9.158(6) Å, andβ=90.44(6)°, a unit cell volume of 2389.9(24) ų, a density of 3.198 Mg m⁻³, and four formula units in the unit cell. Sixteen non-hydrogen atoms and five hydrogen sites were located in the asymmetric unit, the latter on the basis of geometric considerations rather than from Fourier difference maps. Refinement using anisotropic temperature factors for all non-hydrogen atoms and fixed isotropic temperature factors for all hydrogen atoms yielded residuals based onF²(weighted) andFvalues, respectively, of 0.0767 and 0.0340 for observed reflections [F²>2σ(F²)]. The structure contains layers of (CsH₂XO₄)₂that alternate with layers of (CsHXO₄)₃, whereXis P or S. The arrangement of Cs, H, andXO₄groups within the two types of layers is almost identical to that in the end-member compounds, CsH₂PO₄and CsHSO₄-II, respectively. Although P and S each reside on two of the threeXatom sites in Cs₅(HSO₄)₃(H₂PO₄)₂, the number of protons in the structure appears fixed. In addition, the correlation of S–O and S–OH bond distances with O···O distances, where the latter represents the distance between two hydrogen-bonded oxygen atoms, was determined from a review of literature data.     

Ion polarisation-assisted hydrogen-bonded ferroelectrics in liquid crystalline domains

An alkylamide-substituted (−NHCOC₁₀H₂₁) hydrogen-bonded dibenzo[18]crown-6 derivative (1) was prepared to stabilise the ionic channel structure in a discotic hexagonal columnar (Col_h) liquid crystal. The introduction of simple M⁺X⁻ salts such as Na⁺PF₆⁻ and K⁺I⁻ into the ionic channel of 1 enhanced the ionic conductivity of the Col_h phase of the M⁺·(1)·X⁻ salts, with the highest ionic conductivity reaching ∼10⁻⁶ S cm⁻¹ for K⁺·(1)·I⁻ and Na⁺·(1)·PF₆⁻ at 460 K, which was approximately 5 orders of magnitude higher than that of 1. The introduction of non-ferroelectric 1 into the ferroelectric N,N′,N′′-tri(tetradecyl)-1,3,5-benzenetricarboxamide (3BC) elicited a ferroelectric response from the mixed Col_h phase of (3BC)_x(1)_1−x with x = 0.9 and 0.8. The further doping of M⁺X⁻ into the ferroelectric Col_h phase of (3BC)_0.9(1)_0.1 enhanced the ferroelectric polarisation assisted by ion displacement in the half-filled ionic channel for the vacant dibenzo[18]crown-6 of (3BC)_0.9[(M⁺)_0.5·(1)·(X⁻)_0.5]_0.1.

An alkylamide-substituted (−NHCOC₁₀H₂₁) hydrogen-bonded dibenzo[18]crown-6 derivative (1) was prepared to stabilise the ionic channel structure in a discotic hexagonal columnar (Col_h) liquid crystal.     

Synthesis and crystal structure of mixed metal(III) tungstenyl(VI) ortho-pyrophosphates

The series of isotypic anhydrous ortho-pyrophosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, V, Cr, Fe, Mo, Ru, Rh, In, Ir) was obtained via vapor phase moderated solid state reactions in sealed ampoules. The crystal structure of the phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: V, Ru, Rh) was solved from single crystal X-ray data (C2/c, Z = 16). Fairly regular MO₆ and distorted WO₆ octahedra share vertices with PO₄ and P₂O₇ units to form a 3D network. For the ortho-pyrophosphates with M: V³⁺, Cr³⁺, and Fe³⁺ the oxidation state of M is confirmed by magnetic measurements. ³¹P-MAS-NMR spectra of the diamagnetic phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, In, Ir) show surprisingly different isotropic chemical shifts for the seven phosphorus sites. V^III(W^VIO₂)₂(P₂O₇)(PO₄) occurs as equilibrium phase in the quasi-binary system (V_1–xW_x)OPO₄ at x = 0.67 and exhibits a small homogeneity range 0.60 ≤ x ≤ 0.67. The scandium compound shows a fully inverted occupancy of the M sites according to the formulation W(Sc_1/2W_1/2O₂)₂(P₂O₇)(PO₄).     

On the validity of the Avrami theorem in the case of decelerating growth

It is argued that the use of the Avrami theorem, S(t) = 1−e^−S_x(t), is in principle not allowed when applied to overlapping diffusion zones or, more generally, in all cases where the phantom nuclei overtake the front of their parent nuclei. Via computer simulations the overtake effect is shown to exist and is found to be surprisingly small. The use of a modified Avrami equation, S(t) = FS_x(t)·[1 −e^−S_x(t)], is suggested for such cases and the function F[S_x(t)] pertaining to diffusion-controlled growth is reported.     

Synthesis, characterizations and crystal structures of new organoantimony(V) complexes with various isomers of fluoromethylbenzoate ligands

Six new organoantimony(V) complexes containing various isomers of fluoromethylbenzoate ligands [RC₆H₃COO]₂SbPh₃ and [RC₆H₃COO]SbPh₄ [R = 3-F-4-(CH₃) (1, 4), 4-F-2-(CH₃) (2, 5), 5-F-2-(CH₃) (3, 6)] have been synthesized by the reactions of triphenylantimony(V) dichloride or tetraphenylantimony(V) bromide with various isomers of fluoromethylbenzoate ligands in 1:2 or 1:1 stoichiometries. All the complexes have been characterized by elemental analysis, IR and NMR [¹H, ¹³C and ¹⁹F] studies. The crystal structures of complexes 1, 3, 4, 5 and 6 have been determined by X-ray single crystal diffraction. The structure of complexes show that the five-coordinated antimony(V) atom adopts a distorted trigonal bipyramidal geometry. Furthermore, weak but significant intermolecular C–H···O, C–H···F hydrogen bonds, C–H···pi stacking lead to aggregation and assembly of these complexes into 1D and 2D supramolecular frameworks.