Layered Hydrate Research Articles

Structural and Motional Features of a Layered Sodium Hydrous Silicate as Revealed by Solid State NMR

An approach for the investigation of layered alkali metal polysilicate hydrous materials is presented by choosing complementary multinuclear NMR methodologies. New insights into the structural and motional features of magadiite, a layered sodium silicate hydrate, have been gained using 1H, 2H, 29Si and 23Na one- and two-dimensional NMR experiments. Complementary 1H MAS single- and double-quantum studies have proven to be powerful tools in a clear recognition of the nature of hydrous species involved in hydrogen bonding. 1H and 2H MAS experiments permitted us to determine the extent of the mobility of water molecules and provided corroborating evidences of an intralayer, strongly hydrogen bonded character of silanol groups. On the basis of a novel strategy in the analysis of the cross polarization dynamics, it appeared that magadiite contains two types of structurally different Q(3) tetrahedra, as well as two types of sodium ions. The strategy applied in this work might be useful to obtain structural and motional information in the related layered alkali metal silicates, as well as in other classes of nanoporous materials.

Synthesis and Characterization of a New Layered Lithium Zinc Phosphate Hydrate

A new layered lithium zinc phosphate hydrate, Li2Zn(HPO4)2·0.66H2O, isostructural with Na2Zn(HPO4)2·4H2O was prepared by the direct ambient pressure and temperature reaction between zinc 2,4-pentanedionate, phosphoric acid, and lithium hydroxide. The as-prepared sample is monoclinic (a=8.896(8) Å, b=13.092(5) Å, c=10.882(9) Å, and β=115.760(6)°). The prepared solid undergoes three thermal transformations when it is heated from 110 to 600°C. The first two transformations are due to the release of intercalated water molecules and the third one is due to the HPO2−4–P2O4−7 transition.

Synthesis and Characterization of a New Layered Barium Aluminate Containing Six-Membered Rings: BaAl2O3(OH)2·H2O

A new layered barium aluminate hydrate, BaAl2O3(OH)2·H2O, has been synthesized from a hydrothermal system. The compound crystallizes in the orthorhombic space group Pna21 with M=291.33, a=5.642(3) Å, b=9.887(7) Å, c=10.449(6) Å, V=582.9(6) Å3, Z=4, R=0.0288, and RW=0.0744. The structure of the compound consists of aluminate sheets stacked in an ABAB sequence. Each individual sheet contains six-membered rings formed by corner-sharing AlO2(OH)2 tetrahedral units with the terminal OH groups pointing toward the interlayer region in one direction. There are Ba2+ cations and water molecules located between the adjacent aluminate sheets. On the basis of powder X-ray diffraction, the as-synthesized compound converts to the BaAl2O4 phase by thermal treatment at elevated temperatures. The phase transition has also been monitored by infrared spectroscopy.

Reactivity of layered vanadium pentoxide hydrate with ultrafine metal oxide, TiO2 and ZrO2, particles in an aqueous system

The interactions between vanadium pentoxide hydrate (V2O5·nH2O) sol and colloid solutions of ultra fine titanium dioxide TiO2 and zirconium dioxide particles ZrO2 were studied. When mixed with an intrinsic V2O5·nnH2O sol, TiO2 particles in the mixed sol are sandwiched by V2O5·nH2O layer sheets to form intercalation compounds. An Interlayer distance of V2O5·nH2O was increased by this treatment and the surface area was also increased from 7.9 m2 g−1 for the V2O5·nH2O to ca. 50 m2 g−1. When the TiO2 sol was contacted with K-type V2O5·nH2O, microporous nature appeared in the sample and the surface area incrased up to ca. 100 m2 g−1. The porous structure was maintained up to 300°C, above which materials were separated into two phases, anhydrous V2O5 and anatase type TiO2. Ultrafine ZrO2 particles were intercalated stoichiometrically in both intrinsic and K-type V2O5·nH2O giving ZrO2-V2O5·nH2O for all the mixing ratios from ZrO2/V2O5 = 5 to 20. Physico-chemical properties were almost unvaried and the materials were nonporous. Their surface areas are around 50 m2 g−1 for the former and around 60 m2 g−1 for the latter. The layered structure was maintained up to 300°C above which the sample was crystallized into ZrV2O7. The reaction temperature is about 150°C lower than that the heated mixture of ZrO2 and V2O5 powders. The electron microscope observations of the prepared materials showed that the number of the stacked layers was decreased from more than 10 sheets for the sample before intercalation to about 2–4 sheets by exfoliation. This indicates that V2O5·nH2O is exfoliated by ion exchangeably reacting to ultrafine titanium oxide and zirconium oxide particles.

Synthesis and structure of layered fluorine-containing crystal hydrates based on aquacomplexes of noble metals

Crystal hydrates were synthesized based on aquaions of noble metals [M(H2O)6]F3·nH2O, where n = 3–8 and M = Ir, Rh. The structure of the resulting crystal hydrates with three aqueous molecules is characterized by the space group P3, Z = 1 and has a layered form. The positively charged layers [M(H2O)6F2+ which alter with negatively charged layers of the composition ∼-·3H2O, are located perpendicular to the c axis. According to X-ray structural and nuclear magnetic resonance data, the water molecules and the F- ions in the negatively charged layers are disordered.

A New Polymorph of VO2Prepared by Soft Chemical Methods

A novel polymorph of VO2, designated VO2(C), has been prepared by dehydration of the new layered vanadium oxide hydrate, VO2·1/2 H2O. The hydrate is prepared in high yield as a single phase from the hydrothermal reaction of the hydrolyzate of VCl4and NaOH in a molar ratio of 1:4.5 for 96 hours at 200°C. The hydrate crystallizes in the tetragonal space groupI4/mmm, witha=3.7211(6) Å,c=15.421(1) Å,Z=4, andR=0.045 as determined by X-ray single crystal diffraction. The structure consists of layers of VO5square pyramids, each of which shares its four basal edges with four neighboring VO5square pyramids. Water molecules that reside between the layers can be removed reversibly to give the new layered oxide VO2(C).

Preparation and Properties of Layered Silica and Layered Alumino-Silica Hydrate from Natural Apophyllite

Crystalline layered silica hydrates were prepared from a natural apophyllite pretreated with 0.1mol⋅dm-3 hydrochloric acid at 5° or 25°C. In these treatments, a product with higher crystallinity was obtained by acidic treatment at a lower temperature. The two silica hydrates had the different local silica structure, and were found to correspond to the silicas reported as an H-apophyllite and a Silica-AP, respectively. The silica hydrates have a fundamental silica sheet structure of apophyllite, and the structure is destroyed by heating above 200°C due to condensation of silanol groups in the interlayer spaces. On the other hand, a crystalline layered alumino-silica hydrate was also obtained from a natural apophyllite pretreated with an aluminum chloride solution. Formation of four different hydrate phases depended mainly upon pH of the reacting solution and/or temperature in the drying process. The introduced aluminum ion was coordinated tetrahedrally and occupied mainly at the interlayer of the silica sheets. On heating, these alumino-silicates maintained their crystal structures up to ca. 400°C. These results suggested that the introduced aluminum ion should prevent the basal silica sheet distance from narrowing and the silanol groups from condensing. In consequence, the sheet structure of these alumino-silicates were more stabilized thermally than that of the silica hydrate.

Valence State of Cerium Incorporated in Aluminium-Free Layered Silicates

Due to their catalytic, adsorptive and exchange properties aluminium-free layered silicate hydrates are interesting supplements to the well-known crystalline porous zeolites and alumophosphates. To create active sites Cerium ions were introduced into the interlayer space of metal silicate hydrates by an ion exchange process. A Ce/Na ion exchange was carried out with a 0.1N Ce(NO 3 ) 3 -solution at room temperature. Two types of air dried Ce-containing layered silicates, ilerite and magadiite, were analysed by XANES and EXAFS spectroscopy at the Ce L III -edge. Both valence states Ce 3+ and Ce 4+ have been detected but Ce 3+ dominated at all. The ratio of Ce 4+ /Ce 3+ at ilerite was larger than that for magadiite. This result leads to the conclusion, that the local order must be higher around cerium in the ilerite.

A structural consideration of kanemite, octosilicate, magadiite and kenyaite

By comparing data from 29 Si, 1 H and 23 Na NMR studies, new model structures have been proposed for the layered sodium polysilicate hydrates, kanemite, octosilicate, magadiite and kenyaite. These are based on the known structures of the anhydrous silicate, KHSi 2 O 5 , and piperazine silicate (EU19), rather than the known structure of the layered sodium polysilicate hydrate, makatite, which previous authors have used as a basis for their models.

Thermoanalytische Untersuchungen an aluminiumfreien Schichtsilikaten

Aluminium-free layered silicate hydrates (metal silicate hydrates — M-SH) are an interesting supplement to the well-known zeolite-like porous materials, due to their large number of catalytic, adsorptive and ion-exchange properties. By means of a combination of X-ray diffraction investigations and several thermo-analytic methods (TG, DSC, TMA) it could be shown that the properties of magadiite will be influenced by the cations located in the interlayer and the morphology of the as-synthesized magadiite products. In particular, hydration behaviour and phase transformation behaviour of the magadiite will be affected. Thus, H- and Ce-magadiite are stable up to temperatures of about 800‡C, while the as-synthesized Na-forms will loss water irreversible already at about 200‡C, will be dehydroxylated, and will be decomposed structurally at about 400‡C.

1H, 29Si and 1H, 23Na heteronuclear shift correlation in octosilicate via cross-polarisation

Solid-state magic-angle spinning was used to study octosilicate, a layered sodium polysilicate hydrate. Conventional one-dimensional NMR spectra detect two distinct proton and silicon sites and a single sodium species. Heteronuclear shift correlation experiments have shown that only one type of proton is involved in efficient cross-polarisation to all the silicon and sodium sites. Such selectivity could be caused by a favourable position for, and suitable rigidity of, this strongly hydrogen-bonded proton. The latter requirement can be used to propose a simple model of the interlayer space in octosilicate.

Synthesis, structure and catalytic properties of the layered antimony rhenium oxide hydrate (SbOReO4.cntdot.2H2O): location of hydrogen-atom positions by powder neutron diffraction

A new hydrated antimony rhenium oxide, SbOReO[sub 4][center dot]2H[sub 2]O, has been prepared by hydrothermal methods and fully characterized by powder neutron diffraction. The structure consists of double layers built up from infinite, interconnected arrays of [SbO[sup +]][sub n] and ReO[sub 4][sup [minus]] units. Water molecules reside in the interlamellar region, and all four protons are involved in hydrogen bonds which are responsible for holding the structure together. Catalytic activity of dehydrated SbOReO[sub 4][center dot]2H[sub 2]O for the oxidation of ethanol and the aldol condensation of acetone is consistent with acidic behavior. Crystal data: SbOReO[sub 4][center dot]2H[sub 2]O, M[sub r] = 423.98, orthorhombic, space group Pbca (No. 61), a = 5.6952 [angstrom], b = 18.325 [angstrom], c = 11.909 [angstrom], V = 1242.9 [angstrom][sup 3], Z = 8, T = 298 K. Final residuals of R[sub p] = 1.43% and R[sub wp] = 1.84% (x[sup 2] = 1.24) were obtained for 58 parameters and 2600 data points (powder neutron diffraction data). 21 refs., 3 figs., 4 tabs.

Complementarity of optical and incoherent inelastic neutron scattering spectroscopies in the study of proton conducting materials

With the availability of incoherent inelastic neutron scattering (INS) data over spectral ranges comparable to those in optical vibrational (infrared and Raman) spectroscopies, the methods have become truly complementary, and the combination of information they provide particularly suited to the identification of the nature of protonic entities in proton conducting solids. The use of these techniques to recognise the extent of proton transfer to water in strong acid hydrates (e.g. perchloric acid monohydrate), and in layered solid acid hydrates (e.g. aluminium hydrogen sulphate mono- and tetra-hydrates, tin hydrogen phosphate and tungstophosphoric acid hexahydrate) is illustrated, so allowing the spectral fingerprint of oxonium and diaquahydrogen ions to be established. The application of vibrational spectroscopic methods to organic derivatives of layered proton conductors is also shown, with examples including ammonium-, tetramethylammonium- and aniline-exchanged metal hydrogen phosphates.

A layered clathrate hydrate structure of tetrapropyl ammonium fluoride

A layered clathrate hydrate structure of tetrapropyl ammonium fluoride

Vanadyl phosphate dihydrate, a solid acid: the role of water in VOPO4�2H2O and its sodium derivatives Na x (VIV x VV 1?x O)PO4�(2?x)H2O

Sodium-containing intercalates having as general formula Na x VOPOP4·(2−x)H2O (0.25≤x<0.50) have been obtained and characterized. Orthorhombic phases, which essentially maintain the structure of the layered oxide hydrate VOPO4·2H2O result. Intercalated sodium ions act as ‘pillars’. The presence of H3O+ ions in the parent VOPO4·2H2O and also in some reduced phases, is detected. The understanding of the structural role of the water molecules is advanced and the topotactic dehydration/rehydration processes are studied. The formation of a new metastable VOPO4·H2O phase is established.

Neutron diffraction study on the mechanism of the topotactic reduction of 2HTaS 2 electrodes

The dynamic investigation by neutron diffraction of the topotactic reduction of 2HTaS 2 electrodes in K + D 2 O electrolyte to the ionic layered hydrate K + 0.5(D 2O) 0.5[TaS 2] 0.5− is shown to proceed via third-stage K + x (D 2O) y [TaS 2] 3 x− , second-stage K + x (D 2O) y [TaS 2] 2 x− , and first-stage K + x (D 2O) y [TaS 2] x− intermediates. A comparative study by X-ray diffraction on the cathodic intercalation of 2HTaS 2 and 2HNbS 2 electrodes with hydrated main group and transition metal ions reveals analogous behavior; the formation of higher-stage intermediates is supposedly correlated with stable electronic layer states. Influence of kinetic factors is observed for larger guest cations such as transition metal complexes and organic ions. CdI 2-type host lattices with an octahedral environment of intralayer cations shown different reaction pathways, although the occurrence of intermediate states (at least in the nucleation phase) can be demonstrated. It is concluded that the presence of ordered intermediate states is a general phenomenon in topotactic electrode processes of layered dichalcogenides.