Organic metal (EDO-TTF)2PF6 with multi-instability

Abstract

The multi-instability of the electronic structure of (EDO-TTF)₂PF₆, where EDO-TTF means ethylene-dioxytetrathiafulvalene, is reviewed. This complex showed the metal–insulator transition at 280 K associated with distinct molecular deformations. The mechanism is interpreted as the cooperation of Peierls transition, charge ordering, and the order–disorder transition of the countercomponent. The charge ordering pattern in the low-temperature phase is of the novel [0, 0, 1, 1] type. The sensitivity of the electronic state to external perturbations is demonstrated applying not only static but also instantaneous stimuli. In the latter case, the photo-induced phase transition is ultrafast and highly efficient. One photon causes the transition of several hundreds of donor molecules in the low-temperature phase to relax into a highly conducting metastable state within about 1.5 ps. In the early stage of the transient state, the charge ordering of the [1, 0, 1, 0] type occurs. As for the chemical modifications of this material, the partial deuteration of this complex increases the metal–insulator transition temperature. The introduction of a methyl group greatly modulates the electronic structure of the complex, i.e. (methyl-EDO-TTF)₂X (X=BF₄, ClO₄) shows a two-dimensional electronic structure. The working hypotheses for developing the systems with multi-instability are described.     

Organic metal (EDO-TTF)2PF6 with multi-instability

The multi-instability of the electronic structure of (EDO-TTF)₂PF₆, where EDO-TTF means ethylene-dioxytetrathiafulvalene, is reviewed. This complex showed the metal–insulator transition at 280 K associated with distinct molecular deformations. The mechanism is interpreted as the cooperation of Peierls transition, charge ordering, and the order–disorder transition of the countercomponent. The charge ordering pattern in the low-temperature phase is of the novel [0, 0, 1, 1] type. The sensitivity of the electronic state to external perturbations is demonstrated applying not only static but also instantaneous stimuli. In the latter case, the photo-induced phase transition is ultrafast and highly efficient. One photon causes the transition of several hundreds of donor molecules in the low-temperature phase to relax into a highly conducting metastable state within about 1.5 ps. In the early stage of the transient state, the charge ordering of the [1, 0, 1, 0] type occurs. As for the chemical modifications of this material, the partial deuteration of this complex increases the metal–insulator transition temperature. The introduction of a methyl group greatly modulates the electronic structure of the complex, i.e. (methyl-EDO-TTF)₂X (X=BF₄, ClO₄) shows a two-dimensional electronic structure. The working hypotheses for developing the systems with multi-instability are described.     

Cu magic angle spinning (MAS) nuclear magnetic resonance (NMR) study of CuX crystals (X=Cl, Br, and I) and CuX-based glasses (X=Cl, Br, and I)

⁶³Cu MAS NMR spectra of CuX crystals (X=Cl, Br, and I) and CuX-based glasses (X=Cl, Br, and I) have been measured. The CuCl and CuI crystals gave the isotropic chemical shift values around 0 ppm, and the CuBr crystal, around −55 ppm. The peak positions of the chlorocuprate(I), bromocuprate(I), and iodocuprate(I) glasses were very close to those of the CuX crystals, respectively. This result indicates that these glasses mainly consist of CuX₄ tetrahedra (X=Cl, Br, and I). The halogen coordination environments around Cu⁺ in bromochlorocuprate(I) glasses were dependent on the kind of modifying cation and the Br⁻/(Cl⁻+Br⁻) ratio. The bromochlorocuprate(I) glasses were mainly composed of CuCl_mBr_4−m or CuCl_nBr_4−n tetrahedra (m=0, 1, 2, and 4; n=0, 1, and 4).     

The synthesis and characterisation of Co2X (Ba2Co2Fe28O46) and Co2U (Ba4Co2Fe36O60) ferrite fibres, manufactured from a sol-gel process

The X and U phases of hexagonal ferrites are notoriously difficult to make as pure materials, and what little data there is published regarding their physical or magnetic properties relates only to single crystals. Stoichiometric Co₂X and Co₂U fibres were made from a sol-gel based process, and the characteristics of the sols and fibres were studied using PCS, XRD, SEM and VSM. The evolution of the X and U fibres was studied, and shown to be similar that of the W and Z fibres whose structures they respectively resemble. Co₂X and Co₂U had been formed at 1200°C, and the morphology of the fibres was different from those of the W and Z phases. The magnetic properties, again while resembling the W and Z phases, were different to any of the other hexagonal ferrite fibres. The magnetic hysteresis loops of both fibres were magnetically as was, the Co₂X fibres having M _s = 45.0 emu g^–1 and H _c = 0.085 T, and the Co₂U fibres having M _s = 51.5 emu g^–1 and H _c = 0.059 T.     

The thallous chalcogenides Tl6X4Y (X = Cl,Br, I; Y = S,Se)

Single crystals of Tl₆X₄Y(X = Cl, Br, I; Y = S, Se) were prepared by the Bridgman technique. The compounds were characterized by complete X-ray structural analyses. All are isotypic, space group $\text{P}\text{4}\text{mnc}$, with a = 843.3(2) pm, c = 917.2(2) pm for Tl₆Cl₄S, a = 872.1(2) pm, c = 932.8(1) pm for Tl₆Br₄S, a = 917.6(3) pm, c = 960.8(1) pm for Tl₆I₄S and a = 917.8(3) pm, c = 967.5(1) pm for Tl₆I₄Se. FIR spectra as well as photoacoustic spectra are given.     

New quasi one-dimensional AxNb6X8 phases isostructural with Nb3Te4

A large number of new ternary niobium chalcogenides A_xNb₆X₈ with A = Na,K,Rb,Ca,Cu,Ag,In,Zn,Cd,Sn,Pb and Bi, X = S,Te and A = Sn,Pb and Bi, for X = Se have been synthesized by molten salt ion exchange and/or ternary element insertion. TlNb₆X₈ with X = S,Te were prepared for the first time by high temperature methods. The A cations are incorporated into large empty channels of the three-dimensional network structure of Nb₃X₄. The volume of the crystal lattice is nearly independent of the size of the cations. The extent of insertion (the value of x) appears to be limited primarily by electronic effects.     

New coordination networks constructed from N-(4-pyridyl)isonicotinamide

Crystal structures of new coordination polymers of N-(4-pyridyl)isonicotinamide (pia) were prepared and crystallographically characterized. Compound 1, [Cd(pia)(NCS)₂]_n, provides a rectangular, two-dimensional network, which is constructed by a single bridging of the pia ligand and double bridging of the NCS ligands. Compound 2, [Cu(pzdc)(pia)₂]_n (pzdc = pyrazine-2,3-dicarboxylate), forms a fishbone-type, one-dimensional network, which is comprised of –(Cu-pzdc)– chains with pia ligands. The imino-pyridine donor of the pia binds to the chains, in which the other remains free. The π–π and hydrogen bonding interactions between the pia ligands in the adjacent chains provide a three-dimensional structure.     

Systemes CuX (X = Cl,Br)HgS. etude des composes CuHgSX (X = Cl,Br)

Powder samples of CuHgSCl and CuHgSBr have been synthesized, they crystallize in an orthorhombic structure, space group Pbam. The structure is built up of a three dimensional network of SHgS chains in z = 0 planes connected together with CuS₂X₂ (X = Cl, Br) tetrahedrons. S and X atoms build up a distorted cubic centered lattice.     

Phase Stability of the A2Cu3O4X2 (A = Alkaline-Earth; X = Halogen) System

Stability of A ₂ Cu ₃ O ₄ X ₂ (A = Sr, Ba; X =Cl, Br) of the 2342 phase with the Cu ₃ O ₄ plane, which is composed of the Cu(1)O ₂ and extra Cu(2) sublattices, has been studied in the temperature range between 600 °C and 950 °C. Polycrystalline samples of the composition Sr _2–x Ba _x Cu ₃ O ₄ Cl _2–y Br _y were prepared by the solid-state reaction method. From the powder x-ray diffraction analysis, we have made the phase diagram (x vs. y vs. heat-treatment-temperature). It has been found that the 2342 phase becomes stable with increasing x and y at high heat-treatment-temperatures instead of a mixture of CuO and the A ₂ CuO ₂ X ₂ (2122) phase with the CuO ₂ plane. These results can be explained in terms of the structural matching between the Cu ₃ O ₄ plane and the A ₂ X ₂ layer.     

Isomer shifts of the 6.2 keV nuclear transition of Ta-181 in the ternary thallium chalcogen tantalates Tl3TaX4 (X=S,Se)

The isomer shifts of the 6.2 keV nuclear transition of Ta-181 in the compounds Tl₃TaS₄ and Tl₃TaSe₄ were investigated by nuclear gamma resonance spectroscopy. Relative to tantalum metal the isomer shifts measured correspond to ?10.16 ± 0.05 mm/s and +3.85 ± 0.03 mm/s, respectively; they are about 25 mm/s lower than the values of the corresponding isomer shifts of the Cu₃TaX₄ series (X = S, Se). This can be explained by the differences in charge transfer for Tl ← X and Cu ← X. The substitution of S by Se in Tl₃TaS₄ changes the isomer shift in the same measure as the corresponding substitution in Cu₃TaS₄. Taking into account the one Ta valence electron difference, a similar dependence was also found for the corresponding binary chalcogenide series $\text{TaS}{}_2\text{TaSe}{}_2$.     

Preparation and electrical properties of sintered oxides composed of Mn1.5Co(0.25+X)Ni(1.25-X)O4 ( $$0 \leqq X \leqq 0.75$$) with a cubic spinel structure

Monophase cubic spinel-type oxides of Mn_1.5Co_(0.25+X)Ni_(1.25-X)O₄ ( ) were prepared through the oxidation of specimens sintered at 1400 °C. The oxides with composition are focused on in this study, as the oxides with composition did not convert into a monophase cubic spinel structure. The electrical conductivity of the sintered bodies was confirmed to increase exponentially with increasing temperature. In the composition range of , both the electrical conductivity and the Seebeck coefficient increased with increasing X. The oxides with composition between were n-type semiconductors, whereas those with were p-type. It was concluded that electrical conduction in the specimens is controlled by small polaron hopping.     

Effects of substitution of X (X=rhenium,chromium and zirconium) on the properties of Co7Mo6 μ phase: A first‐principles study

The effects of three typical refractory elements (rhenium, chromium and zirconium) substituting the molybdenum atom in Co₇Mo₆ μ phase were investigated using first‐principles calculations based on the density functional theory (DFT). Energy (including binding energy and defect energy) and electronic structures (including density of states and charge density) of Co₇Mo₅X (X=rhenium, chromium and zirconium) were calculated. The optimized lattice structure of Co₇Mo₆ agrees well with the experimental data. The calculated results show the bonding between doped rhenium atom and its nearest neighbor molybdenum and cobalt atoms gets visibly stronger, contributing to the good stability of the unit cell. Neverthless, the bonding between chromium and its nearest neighbor molybdenum and cobalt is weaker, and the zirconium‐molybdenum and zirconium‐cobalt bonds are much weaker. The results reveal rhenium tends to participate in the formation of μ phase, but zirconium and chromium atoms are not prone to concentrate in μ phase.     

Preparation of compounds A2CuCl4−xBrx (A=K,Rb,NH4,Tl; x=0,1,2) and crystal structures of compounds Rb2CuCl4−xBrx with ordered distribution of the anions

The systems AX-CuX₂ (A=K,Rb,NH₄,Tl; X=Cl,Br,I) have been surveyed in search of compounds A₂CuX₄ having the K₂NiF₄ or a related structure. For compounds A₂CuX_4?xX′_x, where x=1,2 and X′ is a halogen ion larger than X, and having such a structure, it is expected that a special ordering exists between the X and X′ anions. The compounds Rb₂CuCl₄,Rb₂CuCl₃Br and Rb₂CuCl₂Br₂ are found to crystallize in the (NH₄)₂CuCl₄ structure which is related to the K₂NiF₄ structure. The expected ordering between C1 and Br ions is demonstrated.     

Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Geometric isomerism of layered complexes of uranyl selenates: Synthesis and structure of (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)] and (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)](H2O)

New uranyl selenates with organic cations (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)] (I) and (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)](H₂O) (II) were synthesized by evaporation of aqueous solutions and studied. Compound I has monoclinic symmetry, space group C2/c, a = 16.7572(13), b = 11.7239(12), c = 19.0490(13) Å, β = 98.875(6)°, V = 3697.6(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.085 for 2868 reflections with |F _hkl | ≥ 4σ|F _hkl |. Compound II has monoclinic symmetry, space group P2₁/n, a = 10.8252(10), b = 19.0007(10), c = 18.6463(15) Å, β = 100.324(7)°, V = 3773.2(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.084 for 5721 reflections with |F _hkl | ≥ 4σ|F _khl |. The structures of I and II are based on layered complexes [(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)]^3? formed by combination of uranyl pentagonal bipyramids and selenate tetrahedra. H₃O⁺ cations, water molecules, and protonated methylbutylamine cations are located in the interlayer space. Geometric isomerism of two-dimensional complexes [(UO₂)₃(SeO₄)₅(H₂O)] in the structures of uranyl selenates was found and described.     

Synthesis and crystal structures of a new (2,3-(CH3)2C6H3NH3)H2XO4 (X=P,As)

The aim of encapsulation of 2,3-dimethylanilinium cation in (H₂XO₄)_n polymeric anion chains is to build acentric frameworks that are efficient for non-linear optical (NLO) applications. The synthesis and structures of two new inorganic–organic NLO crystals with general formula (2,3-(CH₃)₂C₆H₃NH₃)H₂XO₄ (X=P, As) are reported. The magnitude of their second harmonic generations (SHG) responses was found to be between the KDP and urea. They crystallize with monoclinic unit-cells and are isotopic. We have determined the structure of phosphoric salt. The following unit-cell parameters were found: a=8.866(3) Å, b=5.909(6) Å, c=10.644(5) Å, β=112.44(1)°, V=515.5(5) Å³ and D_X=1.412 g cm⁻³. The space group is P2₁ with Z=2. The structure was refined with R=0.041 (R_w=0.057) for 1652 reflections with I≥3σ(I). It exhibits infinite (H₂PO₄)_nⁿ⁻ chains. The organic groups (2,3-(CH₃)₂C₆H₃NH₃)⁺ are anchored between adjacent polyanions through multiple hydrogen bonds. Chemical preparation, crystal structure, calorimetric and spectroscopic investigation are described.     

Evidence for the π-d Interaction Comparing Magnetoresistance in (EDT-DSDTFVO)2 X, X=FeCl4, GaCl4

Hall resistance and magnetic torque measurements have been carried out in the field-induced spin-density-wave (FISDW) phase of deuterated (TMTSF)₂ClO₄ for various cooling rates through the anion ordering temperature. We have found that the Hall resistance in the intermediate cooled state shows a phase transition from the non-quantized Hall phase to the quantized Hall phase (n=1) with hysteresis. We have also found that the magnetic torque in the non-quantized Hall phase rapidly decreases with increasing cooling rate. These results suggest that there is a new phase transition from the non-quantized Hall phase to the quantized Hall phase in (TMTSF)₂ClO₄.     

Isomer shifts of the 6.2 keV nuclear transition of Ta-181 in sulvanite type ternary phases Cu3TaX4 (X=S,Se,Te)

The isomer shift of the 6.2 keV nuclear transition of Ta-181 in Cu₃TaTe₄ was determined by nuclear gamma resonance spectroscopy. The value obtained amounts to +55.95±0.06 mm/s relative to tantalum metal. The isomer shifts in the three isotypic compounds Cu₃TaX₄ are related linearly to the Mulliken electronegativities of the chalcogens X = S, Se, Te. A correlation between isomer shifts and the unit cell volumes is deduced for these compounds in good agreement with the experimental results.     

Quantum Dots of [Na4Cs6PbBr4]8+, Water Stable in Zeolite X,Luminesce Sharply in the Green

Nanocrystals (NCs) of CsPbX₃, X = Cl, Br, or I, have excellent photoluminescent properties: high quantum yield, tunable emission wavelengths (410−700 nm), and narrow emission band widths. CsPbBr₃ NCs show high promise as a green-emitting material for use in wide color gamut displays. CsPbBr₃ NCs have, however, not been commercialized because they are sensitive to moisture and heat. To avoid these problems, this work attempts to introduce CsPbBr₃ into five zeolites. The zeolite X product, Pb,Br,H,Cs,Na−X, shows superior stability toward moisture, maintaining its initial luminescence properties after being under water for more than a month. Its structure, determined using single-crystal X-ray crystallography, shows that quantum dots (QDs) of [Na₄Cs₆PbBr₄]⁸⁺ (not of CsPbBr₃) have formed. They are tetrahedral PbBr₄²⁻ ions (Pb−Br = 3.091(11) Å) surrounded by Na⁺ and Cs⁺ ions. Each fills the zeolite's supercage with its Pb²⁺ ion precisely at the center, a position of high symmetry. The peaks in the emission spectra of Pb,Br,H,Cs,Na−X and the CsPbBr₃ NCs are both at about 520 nm. The FWHM of Pb,Br,H,Cs,Na−X, however, is narrower than any previously reported for any of the CsPbBr₃ NCs, and for zeolite Y and the various mesoporous materials treated with CsPbBr₃.     

Charge and Anion Ordering in (TMTTF)2X Quasi-One-Dimensional Conductors

We present results of measurements of dielectric spectroscopy concerning the 4k_F charge density wave associated with the charge ordering (CO) of Wigner type in (TMTTF)₂X conductors. This CO transition is due to correlated electron interactions on the molecular chains and to the appropriate displacement of the anion chains (transition at q=0). Recent experiments on the substitution of hydrogen by deuterium in TMTTF molecules will be reported. In the vicinity of T_CO it has also been found the divergence of the relaxation time and the development of a low frequency shoulder in the frequency dependence of the imaginary part of the dielectric permittivity, which are typical features for classical ferroelectrics.