Triclinic Modification Research Articles

XPS and NEXAFS Studies of Zn-Doped Bismuth Iron Tantalate Pyrochlore

The effect of Zn-doping on the phase composition and optical properties of the Bi2ZnxFe1-xTa2O9.5-Δ (x = 0.3, 0.5, 0.7) was studied. XRD data showed that the samples crystallize in the structural type of pyrochlore (sp. gr.Fd-3m). For all the samples, an admixture of bismuth orthotantalate β-BiTaO4 triclinic modification up to 22.5 wt.% is observed. The content of β-BiTaO4 increases with zinc doping. The unit cell parameter of the pyrochlore phase rises from 10.4878 (x = 0.3) to 10.5154 Å (x = 0.7). The samples are characterized by a porous microstructure with indistinct grain boundaries. Zinc oxide has a sintering effect on ceramics. The charge state of the ions in Bi2ZnxFe1-xTa2O9.5-Δ was investigated by X-ray spectroscopy. NEXAFS and XPS data show that zinc doping does not change the oxidation degree of iron and bismuth ions in pyrochlore. The ions are in the charge states Bi(+3), Fe(+3), Zn(+2). In the Ta4fspectrum, an energy shift of the absorption band towards lower energies by ΔE = 0.5 eV is observed, which is typical for tantalum ions with an effective charge of (+5-δ). With the increase of x(Zn), the Bi 4f7/2 and Bi 4f5/2 bands are observed to shift to lower energies due to the distribution of some Zn(II) ions in the bismuth position.

Orthorhombic and triclinic modifications of the arsenate Cu4O(AsO4)2 and isotypic phosphates Cu4O(PO4)2: strongly frustrated antiferromagnetics

A structural-magnetic models of the orthorhombic and triclinic modifications of the arsenates Cu4O(AsO4)2 and isotypic phosphates Cu4O(PO4)2 has been built and analyzed. Their base elements are the complicated ribbons composed of antiferromagnetic Cu4 tetrahedra. Structurally, these tetrahedra have no shared copper atoms; however, there are strong antiferromagnetic (AFM) and ferromagnetic (FM) couplings between them, both within the complicated ribbons and between them. It has been established that both modifications are strongly frustrated 3D antiferromagnetics due to competition between the nearest AFM interactions along the edges of the Cu4 tetrahedra and competition between interactions and a multiplicity of long-range secondary AFM and FM interactions. Additionally, a large number of weaker long-range interactions are competing among each other. However, there is a possibility of the ordering Dzyaloshinskii-Moriya (DM) interaction in the centrosymmetric orthorhombic modification (Pnma), because two of the three types of magnetic ions, Cu1 and Cu3, are in the partial position 4c, where the ions are not related by the inversion center. In the triclinic modification (P −1) of Cu4O(As(P)O4)2, all four copper ions are in the centrosymmetric equivalent position 2i, which prevents DM interactions. This centrosymmetry will allow magnetic interactions in the triclinic modification of Cu4O(As(P)O4)2 to be still frustrated at lower temperature. It is possible that the triclinic modification of these compounds is a quantum spin liquid.

Preparation of triclinic alite with short soakings in a small experimental high-temperature furnace

The article deals with a laboratory preparation of triclinic modification of clinker mineral tricalcium silicate. A substantial part of the article is devoted to the technology and technique of firing a sample of tricalcium silicate, which would in the future allow the study of the development of the crystal lattice structure of this clinker mineral at short isothermal durations, in the order of minutes. As part of the research, a small high-temperature experimental furnace was designed and constructed. Based on the results, we can express the suitability and applicability of this furnace for the study of the formation of triclinic tricalcium silicate at short soakings.

Low-temperature phase transition and high-pressure phase stability of 1H-pyrazole-1-carboxamidine nitrate

The phase transition observed in a temperature-dependent experiment at 174 K is unachievable under high-pressure conditions. Negative thermal expansion for phase (II) and negative compressibility for phase (I) were observed. A new salt of 1H-pyrazole-1-carboxamidine, (HPyCA)NO3, for guanylation reaction was obtained in a crystalline form. The compound crystallizes in monoclinic space group P21/c and a phase transition at 174 K to triclinic modification P 1 was found. An unusual increase of the unit-cell volume was observed just after transition. Although the volume decreases upon cooling, it remains higher down to 160 K in comparison to the unit-cell volume of phase (I). The mechanism of the phase transition is connected with a minor movement of the nitrate anions. The triclinic phase was unreachable at room-temperature high-pressure conditions up to 1.27 GPa. On further compression, delamination of the crystal was observed. Phase (I) exhibits negative linear compressibility, whereas abnormal behaviour of the b unit-cell parameter upon cooling was observed, indicating negative thermal linear expansion. The unusual nature of the compound is associated with the two-dimensional hydrogen-bonding network, which is less susceptible to deformation than stacking interactions connecting the layers of hydrogen bonds. Infrared spectroscopy and differential scanning calorimetry measurements were used to investigate the changes of intermolecular interactions during the phase transition.

Lithium-Cation Conductivity of Solid Solutions in Li6-xZr2-xAxO7 (A = Nb, Ta) Systems.

Li6-xZr2-xAxO7 (A = Nb; Ta) system with 0 < x < 0.30 is synthesized by glycine-nitrate method. Boundaries of solid solutions based on monoclinic Li6Zr2O7 are determined; temperature (200–600 °C) and concentration dependences of conductivity are investigated. It is shown that monoclinic Li6Zr2O7 exhibits better transport properties compared to its triclinic modification. Li5.8Zr1.8Nb(Ta)0.2O7 solid solutions have a higher lithium-cation conductivity at 300 °C compared to solid electrolytes based on other lithium zirconates due the “open” structure of monoclinic Li6Zr2O7 and a high solubility of the doping cations.

Packing Polymorphism on the Example of 5-Hydroxy-1-(4-Methylbenzyl)-3-Chloro-4-[(4-Chlorophenyl)Sulfanyl]-1,5-Dihydro-2H-Pyrrol-2-One: A Crystallographic, Thermochemical, and Spectroscopic Study

Two packing polymorphs of 5-hydroxy-1-(4-methylbenzyl)-3-chloro-4-[(4-chlorophenyl)sulfanyl]-1,5-dihydro-2H-pyrrol-2-one are studied by single-crystal and powder X-ray diffraction, IR spectroscopy, and differential scanning calorimetry. Classical hydrogen bonds and CL…O interactions have the fundamental importance for the formation of the supramolecular motif that is identical in both modifications. The difference relates to the packing of 2D layers which is “parallel” in the triclinic modification and of the “herringbone” type in the monoclinic modification. It is shown that close similarity between structural organizations of crystal lattices, which is typical of packing polymorphs, can be accompanied by significant differences between their energies as well as by a high potential barrier upon the transition from the metastable polymorph to its stable form.

Supramolecular interactions and self-assembling in adducts of cymantrenecarboxylic acid with amino derivatives of five- and six-membered heterocyclic N-bases

The structures of eleven new derivatives of cymantrenecarboxylic acid with heterocyclic N-bases as well as with ethanolamine were characterized by X-ray analysis. Depending on the strength of the bases, the complexes are either ionic salts in which the N atoms of the aromatic ring are protonated, or supramolecular adducts in which the carboxylic acid protons form hydrogen bonds. In the structures of compounds, the various supramolecular interactions take place due both to the specific geometry of the cymantrene fragment and to the geometry of the N-base. It was shown that the location of the H-bond donor and acceptor fragments of the base molecules is a factor determining the self-assembly. The crystal structure of the triclinic modification of cymantrenecarboxylic acid was described for the first time.

Thermal analysis and high-temperature X-ray diffraction study of BiNbO4

Phase transformations of bismuth orthoniobate BiNbO4 were studied by the methods of differential scanning calorimetry and high-temperature X-ray diffraction. The DSC curve in the heating–cooling mode of the orthorhombic samples (α-BiNbO4) showed endothermic and exothermic effects associated with the phase transition from the orthorhombic modification to the triclinic one at the temperatures of ~ 1328 K and ~ 1270 K. This phase transition passed through a high-temperature phase of γ-BiNbO4, in which reflections were indicated in the temperature range of 1323 K → 1353 K → 1263 K. The X-ray diffraction pattern of the sample quenched in air (77 K) and calcined at the temperature from this range, 1323 K, corresponded to the triclinic modification. During the heating, the triclinic modification (β-BiNbO4) was transformed into the high-temperature phase of γ-BiNbO4, which was stable up to ~ 1270 K. Then, it was transformed into the triclinic modification again. The DSC curve of the sample of triclinic BiNbO4 showed endo- and exothermic effects at temperatures of ~ 1274 K and ~ 1270 K associated with the transition into the high-temperature phase of γ-BiNbO4. The cooling of the sample leads to the phase transition from the triclinic to the orthorhombic modification of BiNbO4. Thermostating at 1223 K for 1 h and quenching in air the compact sample or dispersed powder of bismuth orthoniobate of the triclinic modification led to the formation of the orthorhombic modification.

Subsolidus phase relations and structures of solid solutions in the systems K2MoO4–Na2MoO4–MMoO4 (M = Mn, Zn)

Study of phase formation in the system K2MoO4–Na2MoO4 at 500 °C showed the existence of the only double molybdate K2-xNaxMoO4 (0.4 ≤ x ≤ 1) of the glaserite-related type. Using these data, the subsolidus phase relations in the systems K2MoO4–Na2MoO4–MMoO4 (M = Mn, Zn) were studied at 470–560 °C and the extended solid solutions based on the alluaudite-type Na4−2xM1+x(MoO4)3 were found. In the structure of K1.71Na1.71Mn1.29(MoO4)3 (sp. gr. C2/c, Z = 4, a = 13.0595(3) Å, b = 13.7892(3) Å, c = 7.2973(2) Å, β = 111.339(1)°, R = 0.0134), the potassium ions partially replace Na+ in the channels running along c-axis. The structure of K1.84Na2.11Zn1.02(MoO4)3 (sp. gr. P1̅, Z = 2, a = 7.3258(8) Å, b = 9.4128(10) Å, c = 9.4302(10) Å, α = 93.104(3)°, β = 104.573(3)°, γ = 104.432(3)°, R = 0.0220) is isotypic with alluaudite-related α-K4Zn(WO4)3 and seems to be a result of stabilizing an unknown triclinic modification of K4Zn(MoO4)3 by substitution of sodium for potassium with the strong differentiation of alkali and zinc cations in the structure. In the structure of K1.5Na0.5Mn2(MoO4)3 (sp. gr. Pcca, Z = 8, a = 10.6160(7) Å, b = 12.2714(8) Å, c = 18.0275(11) Å, R = 0.0155) of the α-K2Mn2(MoO4)3 type, one of three initial potassium positions is jointly occupied by (Na, Mn); a similar phenomenon occurs in isostructural Rb3Na3Sc2(MoO4)6. The structure contains zigzag-like ribbons of edge-sharing MnO6 octahedra linked with separate MnO6 octahedra and МоО4 tetrahedra into 3D containing channels along the c-axes filled by K+ ions. BVS maps show possible one-dimensional sodium-ion conductivity for the structures of K1.71Na1.71Mn1.29(MoO4)3 and Rb3Na3Sc2(MoO4)6.

Phase transition of BiNb1−xMnxO4−δ: Thermal analyse, NEXAFS, XPS and ESR-study

Abstract The manganese-doped polymorphs of bismuth orthoniobate were studied using thermal analysis, ESR, XPS and NEXAFS spectroscopy. It was shown that the phase transition from the orthorhombic (α) to the triclinic (β) modification can be reversible and it can be achieved by prolonged calcination of samples at 750°C. The DSC curves revealed no thermal effects associated with the phase transformation from the triclinic to the orthorhombic modification near 750°C. In the ESR spectra, the absorption band with g = 3.8 characterized by sextet structure disappeared during the phase transformation from the - to the -form and only the broad component with average intensity was observed at g = 2.2-2.0. According to NEXAFS spectroscopy data, the content of oxidized Mn(III) atoms increased and the content of Mn(II) decreased in the orthorhombic polymorph obtained at 750°C from the tri-clinic modification.

Phase transformations and thermal stability of Ni-doped BiNbO4 ceramics

Phase transformations and thermal stability of nickel-containing solid solutions of bismuth orthoniobate BiNbO4 were studied by methods of thermal and X-ray phase analysis. The DSC curve of the BiNb1-xNixO4-δ samples exhibited endothermic effects near the temperatures of 1049 °C and 1227 °C during the heating, and exothermic effects at ˜990 °C during the cooling, which were associated with the phase transition from the orthorhombic to triclinic modification and with congruent melting. In the compacted polycrystalline samples of the solid solutions, the phase transition from the high-temperature triclinic modification to the orthorhombic modification was revealed after calcination at 750 °C for 150 h, as well as after 1 h calcination at 950 °C.

High-Temperature Studies of the Structure of Complex Oxides Based on Bi26Mo10O69–d

Complex oxides with the general formula Bi26–2xMe2x′ Mo10O69–d, Bi26Mo10–2yMe2y′′ O69–d are synthesized by the standard ceramic technology, certified and analyzed by high-temperature X-ray and neutron diffraction techniques. Specific features of the structures of triclinic and monoclinic modifications of complex oxides are determined. It helps interpret a change in the electroconductive properties of the samples as a result of a polymorphic transition: in the monoclinic modification [MoO4–O–MoO4] clusters are detected together with a doubled amount of [(MoO4)–Bi(MoO4)–]n chains oriented along the b axis, which may affect the character of oxygen ion transfer. For Fe-substituted samples selective iron substitution for molybdenum is revealed.

Mn doped BiNbO4 ceramics: Thermal stability, phase transitions, magnetic properties, NEXAFS and ESR spectroscopy

Thermal stability, magnetic properties, ESR (Electron Spin Resonance) and NEXAFS (Near-Edge X-ray Absorption Fine Structure) spectra of the orthorhombic and triclinic modifications of solid solutions BiNb1-xMnxO4-δ have been studied. X-ray diffraction determined the reversibility of the phase transition from the high-temperature triclinic modification to the orthorhombic modification at 950 °C in the BiNb1-xMnxO4-δ solid solutions. The ESR spectra of the triclinic BiNb1-xMnxO4-δ revealed the sextet structure of Mn(II) ions with 8.4 mT splitting and some features at g = 3.80 and 1.47, and a broad diffuse band with g ∼ 2.2 having a sextet with 8–9 mT splitting and g = 2.0 against its background. The measurements of magnetic susceptibility allowed us to calculate the parameters of exchange interactions in dimers and the distribution of manganese atoms (II), (III) and (IV) in dependence on concentrations of the solid solutions in the orthorhombic and triclinic modifications. It was established that in the manganese-doped solid solutions of triclinic modification, the degree of aggregation and the nuclearity of the clusters were higher than in the solid solutions of orthorhombic modification. The clusters were presented in the forms of dimers and trimers of Mn(II), Mn(III) and Mn(IV) atoms with different valence atoms with antiferro- and ferromagnetic types of exchange.The solid solutions BiNb1-xMnxO4-δ as well as manganese oxides MnO, Mn2O3 and MnO2 were studied by the NEXAFS spectroscopy in order to determine the degrees of oxidation of manganese atoms. The DSC (Differential Scanning Calorimetry) curves of the samples BiNb1-xMnxO4-δ revealed the endothermic effects associated with the phase transition from the orthorhombic modification to the triclinic one at 1050 °C (x = 0.03) and 1048 °C (x = 0.06). The melting peaks were observed at 1231 °C (x = 0.03) and 1220 °C (x = 0.06), respectively. The differences in the magnetic characteristics and in the results of ESR and NEXAFs spectroscopy of the BiNb1-xMnxO4-δ of orthorhombic and triclinic modifications were due to the relative content of Mn(II), Mn(III), Mn(IV) ions and the degree of distortion of their local surroundings, composition and nature of exchange interactions in the clusters of manganese atoms.

EPR and NEXAFS spectroscopy of BiNb1-xFexO4-δ ceramics

The methods of EPR and NEXAFS spectroscopy were employed for the study of BiNb1-xFexO4-δ solid solutions of triclinic and orthorhombic modifications. The analysis of the NEXAFS Fe2p-spectra of iron oxides and the iron-containing solid solutions revealed that Fe atoms were mainly in an oxidation state of +3. In the EPR spectra of the BiNb1-xFexO4-δ samples of orthorhombic modification, a broad line with the center at g of 2.16–2.37 was registered along with the low-intensity signal with a g-factor of ∼4.3 observed on its low-field wing. EPR spectra of the triclinic structure samples exhibited a complex system of lines in the range of 80–300 mT. An intense complex line having features at g of 4.74–4.80, 4.04–4.10 and 3.76–3.80 was recognized in the low-field signal. The low-field wing of the line was complicated by a shoulder with g of 5.3 and by a line in the form of an absorption signal with g of 7.7–8.0. As a result of the modeling of EPR spectra, the spin-Hamiltonian parameters of Fe(III) in the structure of BiNb1-xFexO4-δ of triclinic modification were obtained.

Phase Formation Studies of Lead(II) Copper(II) Oxotellurates: The Crystal Structures of Dimorphic PbCuTeO5, PbCuTe2O6, and [Pb2Cu2(Te4O11)](NO3)2

Two modifications of the oxotellurate(VI) PbCuTeO5 were isolated as single crystals from product mixtures obtained from solid state reactions, whereas single crystals of the oxotellurates(IV) PbCuTe2O6 and [Pb2Cu2(Te4O11)](NO3)2 were grown under hydrothermal conditions. The crystal structures of all compounds comprise of characteristic coordination polyhedra, viz. nearly square [CuO4] plaquettes for divalent copper, octahedral [TeO6] units for hexavalent tellurium, trigonal‐pyramidal [TeO3] and bisphenoidal [TeO4] groups for tetravalent tellurium, and distorted [PbOx] polyhedra for divalent lead. PbCuTeO5 is dimorphic and crystallizes in a monoclinic and a triclinic modification, related by a translationengleiche group‐subgroup relation of index 2. PbCuTe2O6 represents the ideal composition of the rare mineral choloalite. The characteristic feature of the crystal structure of [Pb2Cu2(Te4O11)](NO3)2 is its layered set‐up, comprised of cationic [Pb2Cu2(Te4O11)]2+ ribbons (width approximately 6.7 Å) sandwiched between nitrate anions that are only weakly bound to the cationic layers.

The [4 + 4] thermocyclization of 9-anthraldehyde: synthesis, crystal structure, experimental and theoretical UV spectra, natural bonding orbital analysis and prediction of third-order nonlinear optical properties.

The dimer of 9-anthraldehyde, namely heptacyclo[8.6.6.62,9.03,8.011,16.017,22.023,28]octacosa-3,5,7,11,13,15,17(22),18,20,23(28),24,26-dodecaene-1,9-carbaldehyde, C30H20O2, has been synthesized by refluxing an ethanol solution in the presence of M(ClO4)2 and 1,3-diaminopropan-2-ol (M = Co2+ or Cu2+). Its structure has been determined by single-crystal X-ray diffraction, showing it to be a new polymorph, referred to as polymorph II, in the monoclinic space group P21/n. It is compared with the previously reported triclinic modification [Ehrenberg (1968). Acta Cryst. B24, 1123-1125], which is referred to as polymorph I. The asymmetric unit of polymorph II contains two half molecules located on crystallographic centres, while the asymmetric unit of polymorph I includes one half molecule, also located on a crystallographic centre. Time-dependent density functional theory (TD-DFT) at the RB3LYP level using the 6-31G(d,p) basis set was applied. The predicted electronic absorption spectrum is in good agreement with the experimental one. The analysis of the calculated electronic absorption spectrum of polymorph II was carried out in order to assign the observed electronic transitions and to determine their character. A natural bonding orbital (NBO) analysis was executed at the same level to evaluate charge-transfer, intramolecular hydrogen-bonding interactions and hyperconjugative interactions. The third-order nonlinear optical (NLO) properties of the compound were appraised by the ZINDO/sum-over-states method in both static and dynamic states. The orientationally averaged (isotropic) value of γ for the compound is greater than the corresponding value of 4-nitroaniline (pNA).

Study of the Conditions for the Biosynthesis of Bacterial Cellulose by the Producer Medusomyces gisevii Sa-12

The effect of culture conditions on the bacterial cellulose (BC) yield synthesized by symbiotic culture Medusomyces gisevii Sa-12 grown in synthetic nutrient medium was studied for the first time. The conditions providing the maximum yield of bacterial cellulose were evaluated: the initial glucose concentration in the culture medium was 20–25 g/L, the temperature was 24–27°C, the ratio of the nutrient medium to the air volume was 1: 10, and the content of the black tea extracts comprised 1.6–4.8 g/L. A sample of chemically pure BC with the following characteristics was obtained under the selected culture conditions: moisture— 99.0%, degree of polymerization—4800, average width of microfibrillar ribbons—30.6 nm, degree of crystallinity— 86%, and the content of triclinic modification Iα—98%.

A monoclinic modification of (4Z)-1-benzyl-4-(2-oxopropylidene)-2,3,4,5-tetrahydro-1H-1,5-benzodiazepin-2-one

In the title molecule, C19H18N2O2, the orientation of the oxopropylidene substituent is largely determined by an intramolecular N—H...O hydrogen bond. In the crystal, C—H...O hydrogen bonds form zigzag chains, which are elaborated into sheets lying parallel to (101) by complementary C—H...π interactions. Comparisons to the structure of the triclinic modification are made.

A Polymorphic Gold(III) Complex Comprising a Multifunctional Triazolylpropanamide Ligand

Reaction of HAuCl4·4H2O with the multifunctional ligand 3‐(1H‐1,2,4‐triazol‐1‐yl)propanamide (1, TPA) afforded the polymorphic gold(III) complex AuCl3(TPA) (2) in 75 % yield. Thermal decomposition of the latter revealed the hydrochloride [HTPA]Cl (3). Complex 2 forms a stable monoclinic and a metastable triclinic modification. The crystal structures of both modifications feature infinite supramolecular assemblies formed by secondary Au···Cl bonding interactions and hydrogen bonding.

Phase transitions and magnetic properties of BiNb1−xFexO4−δ

Magnetic susceptibility of the iron-containing solid solutions BiNb1−xFexO4-δ in orthorhombic and triclinic modifications has been studied. The reversibility of the phase transition from the high-temperature triclinic modification to the orthorhombic one has been revealed by means of magnetic dilution and X-ray phase analysis by the example of polycrystalline samples of the solid solutions BiNb1−xFexO4-δ.