Substitution clustering in a non-stoichiometric celsian synthesized by the thermal transformation of barium exchanged zeolite X

The thermal transformation of Ba exchanged zeolite X to celsian has been studied by ²⁷Al and ²⁹Si MAS NMR spectroscopy. Evidence for the degradation of the zeolite framework is present in the ²⁹Si NMR spectra after thermal treatment at 850 °C. Confirmation is provided by the ²⁹Si NMR data that synthesis of celsian via the decomposition of Ba exchanged zeolite leads to a single defect phase. Clustering of the isomorphous replacement of aluminium by silicon must occur to explain the observed ²⁹Si chemical shifts. The ²⁷Al NMR data show distorted aluminium co-ordination sites upon the thermal transformation of Ba exchanged zeolite X. The distortions present in the amorphous matrix are greater than those present in the monoclinic and hexagonal crystalline phases of celsian.     

Ion association in solutions of dimethylthallium(III) hydroxide

From studies of the specific hydroxide ion catalyzed decomposition of diacetone alcohol by dimethylthallium(III) hydroxide at 25°C, it is concluded that both ion pairs (dissociation constantK=0.090 mole-dm^–3) and dimers (dimerization constantK _d=1.5 dm³-mole^–1) exist in aqueous solution.Request for reprints should be addressed to: Dr. A. D. Pethybridge, Department of Chemistry, The University, Whiteknights Park, Reading, Berkshire, England.Deceased October 16, 1972.     

29Si-NMR-Untersuchungen zur Verteilung der Silicium-und Aluminiumatome im Alumosilicatgitter von Zeolithen mit Faujasit-Struktur

²⁹SiNMR Investigation of Silicon-Aluminum Ordering in the Aluminosilicate Framework of Faujasite-Type Zeolites The high resolution magic angle spinning ²⁹Si NMR spectra of a series of NaX and NaY zeolites with Si/Al ratios of 1.18 to 67 exhibit up to five sharp signals which could be assigned to the central silicon atoms of Si(OSi)_4–n(OAl)_n building units (n = 0–4) of the aluminosilicate framework. From the signal intensities the quantitative distribution of the building units and the Si/Al ratio of the aluminosilicate lattice have been estimated. By comparison of the building units obtained from the ²⁹Si NMR spectra with those from theoretical model structures detailed information on silicon-aluminum ordering of the zeolite framework has been derived. Except for NaX of Si/Al = 1.4 a centrosymmetrical distribution of Si and Al atoms within a double-cubooctahedra unit has been found which agrees well with the Si/Al ordering scheme proposed by Dempsey.     

29Si-NMR-Untersuchungen zur Anionenstruktur von Kristallinen Tetramethylammonium-alumosilicaten und -alumosilicatlösungen

²⁹Si NMR Investigations on the Anion Structure of Crystalline Tetramethylammoniumaluminosilicates and -aluminosilicate Solutions The ²⁹Si NMR spectra of crystalline tetramethylammonium (TMA) aluminosilicates with different Si/Al ratios exhibit up to 4 sharp signals with characteristic chemical shifts which can be assigned to the central Si atom of OSi(OSi)_3?n(OAl)_n building units of double four-ring (DFR) aluminosilicate anions. The number and distributions of the Al atoms in the DFR framework can be derived from the signal intensities in connection with the results of the trimethylsilylation method [1]. A good agreement of the results of both methods has been found. The DFR can exist as monomeric unit or can be connected to polymeric structures by SiOAl bridges, but no information can be obtained about this question by the ²⁹Si NMR spectra. The investigation of the TMA aluminosilicate solutions by ²⁹Si NMR and TMS method [1] show that stable aluminosilicate anions exist in these solutions. The structure of these aluminosilicate anions is different from the structure of the crystalline TMA aluminosilicates obtained from the solutions.     

One-step synthesis of hydrothermally stable mesoporous aluminosilicates with strong acidity

Using tetraethylorthosilicate (TEOS), polymethylhydrosiloxane (PMHS) and aluminium isopropoxide (AIP) as the reactants, through a one-step nonsurfactant route based on PMHS-TEOS-AIP co-polycondensation, hydrothermally stable mesoporous aluminosilicates with different Si/Al molar ratios were successfully prepared. All samples exclusively showed narrow pore size distribution centered at 3.6 nm. To assess the hydrothermal stability, samples were subjected to 100 °C distilled water for 300 h. The boiled mesoporous aluminosilicates have nearly the same N₂ adsorption-desorption isotherms and the same pore size distributions as those newly synthesized ones, indicating excellent hydrothermal stability. The ²⁹Si MAS NMR spectra confirmed that PMHS and TEOS have jointly condensed and CH₃ groups have been introduced into the materials. The ²⁷Al MAS NMR spectra indicated that Al atoms have been incorporated in the mesopore frameworks. The NH₃ temperature-programmed desorption showed strong acidity. Due to the existence of large amount of CH₃ groups, the mesoporous aluminosilicates obtained good hydrophobicity. Owing to the relatively large pore and the strong acidity provided by the uniform four-coordinated Al atoms, the excellent catalytic performance for 1,3,5-triisopropylbenzene cracking was acquired easily. The materials may be a profitable complement for the synthesis of solid acid catalysts.     

Li+(TMPAND)Na−: The first alkalide prepared from an azacage complexant

The new lithium-selective complexant 5,12,17-trimethyl-1,5,9,12,17-pentaazabicyclo[7.5.5]nonadecane (TMPAND) was used to synthesize Li⁺(TMPAND)Na–, the first alkalide prepared from an azacage complexant. This sodide was characterized by a variety of methods. Differential scanning calorimetry experiments showed a reversible, endothermic, solid-solid phase transition at an onset temperature of –75 ± 3°C and with H = 3.3 ± 1 kJ/mol.²³Na NMR spectra showed a peak at –61 ppm, characteristic of a sodium anion, and a second minor peak at –10 ppm, probably due to the interaction of Na- with trapped electrons. The quadrupole coupling constant of the complexed lithium cation was found to be 0.19 MHz at –100°C, and⁷Li NMR spectra showed a discontinuity in the line width of the⁷Li NMR peak and in the quadrupole coupling constant at the phase transition.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Surface Modification of Colloidal Silica by Sulfonation Route for Super-Hydrophilicity

Colloidal silica was chemically modified by a two-step method including an olefin sulfonation route as a preliminary study for super-hydrophilic applications. The hydrophobic vinyl groups were initially bonded chemically to the hydroxylated silica surface using the trichlorosilane coupling agents. The vinyl-terminated silica was then sulfonated by addition reaction with chlorosulfonic acid. The modified silica was investigated using DRIFT, TGA, element analysis, solid-state ²⁹Si- and ¹³C CP-MAS NMR. The vinyl-terminated specimen showed a characteristic IR absorption band at 1600 cm^–1 and a weight loss of approximately 3% starting at 350°C while the ²⁹Si NMR peaks at 70.9 and 79.8 ppm and ¹³C NMR at 136 ppm and 129.8 ppm were assigned to a vinyl group bonded to silica. Elemental analysis of the sulfonated silica indicated the presence of sulfur, carbon and hydrogen. Thermal decomposition in range 150–600°C was due to the presence of sulfonated organics and unreacted vinyl groups while the new signals on ¹³C NMR, which were in the range 70–15 ppm, were assigned to sulfonated carbons.     

Building block approach to organic/silica hybrid materials

The reaction of the cubic octameric silicate anion, Si₈O ₂₀ ^8– , with dimethyldichlorosilane in 2,2-dimethoxypropane yielded solid products. FT-IR and solid-state ²⁹Si NMR spectra of the products indicate that the silicate anion becomes cross-linked via the dimethylsilyl group without degradation of the cubic core, resulting in the formation of organic/silica hybrids consisting of the Si₈O ₂₀ ^8– structure as a building block. The hybrids are thermally stable up to ca. 380°C in air. The specific surface area of the hybrids is 31 m² g^–1, while the value increases to 339 m² g^–1 after calcination at 350°C in air. The process of increasing the surface area of the hybrids by the heat-treatment was investigated using solid-state ¹³C NMR spectroscopy.     

1H and13C spectra of biologically active compounds X. Two-dimensional HH COSY 45° and CH HET CORR spectra of the 18α- and 18β-isomers of glycyrrhetic acid 3-acetate

An assignment of¹H and¹³C NMR signals has been made by the methods of homonuclear two-dimensional spectroscopy, HH COSY (45°), and heteronuclear correlation spectroscopy, CH HET CORR. It has been shown that the range of diastereomeric effects in the¹³C NMR spectra substantially exceeds the effects due to solvents, in contrast to the proton spectra in which these ranges overlap.Institute of Chemistry, Bashkir Scientific Center, Urals Branch, Academy of Sciences of the USSR, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 363–368, May–June, 1991.     

Spectra and structure of silicon containing compounds

The Raman (50 to 3200 cm^–1) and infrared (50 to 3500 cm^–1) spectra of chlorodimethylmethoxysilane, Cl(CH₃)₂SiOCH₃, in the vapor and solid phases have been recorded. Raman spectra of the liquid including depolarization ratios have also been recorded. Optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing the RHF/3–21G* and RHF/6–31G* basis sets. The calculations from both of these basis sets indicated the gauche conformer to be significantly more stable than the trans conformer. Since the gauche has twice the multiplicity of the trans form it is unlikely that the trans conformer will be detected in the fluid phases at room temperature. This is supported by the fact that no infrared or Raman bands were found to vanish in the spectra of the crystalline solid. The vibrational frequencies have been calculated using appropriate scaling factors, and the vibrational spectra are interpreted in detail. The results have been compared with those obtained for some related molecules.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthdayFor part XX, see J Raman Spectrosc 26:in press (1995)Analytical R/D Department, Organic Products Division, Miles Inc., Bushy Park Plant. Charleston, SC 9411, USAChemistry Department, Mu'tah University, P.O.Box 7, Mu'tah-Karak, JordanDepartment of Chemistry, Moscow State University, Moscow, B-234, RussiaDepartment of Ceramic Engineering, Inha University, Nam-Ku, Incheon 160, KoreaDepartment of Chemistry, University of Oslo, P.O.Box 1033, 0315 Oslo, Norway     

NAA determiantion of iron and silicon in USGS standards and bauxites using fast neutrons from241Am-Be source

Fast neutron-activation methods have been developed for the determination of iron and silicon in USGS and Indian standards and bauxites. Nuclear reactions⁵⁶Fe/n, p/⁵⁶Mn and²⁸Si/n, p/²⁸Al were carried out using²⁴¹Am-Be neutron source and cutting off thermal neutrons with a Cd shield. For Si a cyclic method was adopted due to short half life of²⁸Al /2.3 min/. The methods are non destructive, fast, economic and ideal for bulk analysis of rocks and process control.A part of this work was presented at the International Symposium on Nuclear Analytical Chemistry, Slowpoke Reactor Facility, Dalhousie University, Canada, June 5–7, 1985.     

High magnetic field solid‐state NMR analyses by combining MAS,MQ‐MAS,homo‐nuclear and hetero‐nuclear correlation experiments

A general strategy of structural analysis of alumina silicate by combining various solid‐state NMR measurements such as single pulse, multi‐quantum magic angle spinning, double‐quantum homo‐nuclear correlation under magic angle spinning (DQ‐MAS), and cross‐polarization hetero‐nuclear correlation (CP‐HETCOR) was evaluated with the aid of high magnetic field NMR (800 MHz for ¹H Larmor frequency) by using anorthite as a model material. The high magnetic field greatly enhanced resolution of ²⁷Al in single pulse, DQ‐MAS, and even in triple‐quantum magic angle spinning NMR spectra. The spatial proximities through dipolar couplings were probed by the DQ‐MAS methods for homo‐nuclear correlations between both ²⁷Al–²⁷Al and ²⁹Si–²⁹Si and by CP‐HETCOR for hetero‐nuclear correlations between ²⁷Al–²⁹Si in the anorthite framework. By combining various NMR methodologies, we elucidated detailed spatial correlations among various aluminum and silicon species in anorthite that was hard to be determined using conventional analytical methods at low magnetic field. Moreover, the presented approach is applicable to analyze other alumina‐silicate minerals. Copyright © 2012 John Wiley & Sons, Ltd.     

Factor analysis of 27Al MAS NMR spectra for identifying nanocrystalline phases in amorphous geopolymers

Nanostructured materials offer enhanced physicochemical properties because of the large interfacial area. Typically, geopolymers with specifically synthesized nanosized zeolites are a promising material for the sorption of pollutants. The structural characterization of these aluminosilicates, however, continues to be a challenge. To circumvent complications resulting from the amorphous character of the aluminosilicate matrix and from the low concentrations of nanosized crystallites, we have proposed a procedure based on factor analysis of ²⁷Al MAS NMR spectra. The capability of the proposed method was tested on geopolymers that exhibited various tendencies to crystallize (i) completely amorphous systems, (ii) X‐ray amorphous systems with nanocrystalline phases, and (iii) highly crystalline systems. Although the recorded ²⁷Al MAS NMR spectra did not show visible differences between the amorphous systems (i) and the geopolymers with the nanocrystalline phase (ii), the applied factor analysis unambiguously distinguished these materials. The samples were separated into the well‐defined clusters, and the systems with the evolving crystalline phase were identified even before any crystalline fraction was detected by X‐ray powder diffraction. Reliability of the proposed procedure was verified by comparing it with ²⁹Si MAS NMR spectra. Factor analysis of ²⁷Al MAS NMR spectra thus has the ability to reveal spectroscopic features corresponding to the nanocrystalline phases. Because the measurement time of ²⁷Al MAS NMR spectra is significantly shorter than that of ²⁹Si MAS NMR data, the proposed procedure is particularly suitable for the analysis of large sets of specifically synthesized geopolymers in which the formation of the limited fractions of nanocrystalline phases is desired. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterisation of Siliceous Extra‐Framework Species in DAY Zeolites by 29Si MAS NMR and IR Spectroscopic Measurements

Dealuminated Y zeolites (DAY) were obtained by steaming of NH₄NaY at temperatures between 450 °C and 700 °C. They were characterised by means of ²⁷Al and ²⁹Si MAS NMR, IR spectroscopic and XRD measurements. The Si/Al framework ratios of samples were calculated using the ²⁹Si MAS NMR signal intensities, the wave numbers of the double‐ring vibration band w_DR and the asymmetrical TOT valence vibration w_TOT of IR spectra as well as the XRD lattice constant a₀. In contrast to actual Si/Al ratio obtained from w_DR and a₀, the NMR spectroscopic and w_TOT values were determined to be too high because of the superposition of the signals coming from dealuminated zeolite framework and silica gel which forms in the zeolite as a result of steaming. The differently determined Si/Al ratios characterise the siliceous extra‐framework species.     

Solid-state Al and Si NMR characterization of hydrates formed in calcium aluminate-silica fume mixtures

Partially deuterated Ca₃Al₂(SiO₄)_y(OH)_12−4y-Al(OH)₃ mixtures, prepared by hydration of Ca₃Al₂O₆ (C₃A), Ca₁₂Al₁₄O₃₃ (C₁₂A₇) and CaAl₂O₄ (CA) phases in the presence of silica fume, have been characterized by ²⁹Si and ²⁷Al magic-angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopies. NMR spectroscopy was used to characterize anhydrous and fully hydrated samples. In hydrated compounds, Ca₃Al₂(OH)₁₂ and Al(OH)₃ phases were detected. From the quantitative analysis of ²⁷Al NMR signals, the Al(OH)₃/Ca₃Al₂(OH)₁₂ ratio was deduced. The incorporation of Si into the katoite structure, Ca₃Al₂(SiO₄)_3−x(OH)_4x, was followed by ²⁷Al and ²⁹Si NMR spectroscopies. Si/OH ratios were determined from the quantitative analysis of ²⁷Al MAS-NMR components associated with Al(OH)₆ and Al(OSi)(OH)₅ environments. The ²⁹Si NMR spectroscopy was also used to quantify the unreacted silica and amorphous calcium aluminosilicate hydrates formed, C-S-H and C-A-S-H for short. From ²⁹Si NMR spectra, the amount of Si incorporated into different phases was estimated. Si and Al concentrations, deduced by NMR, transmission electron microscopy, energy dispersive spectrometry, and Rietveld analysis of both X-ray and neutron data, indicate that only a part of available Si is incorporated in katoite structures.     

Structural Development of Single Phase (Type I) Mullite Gels

Single phase (type I) mullite gels were prepared by sol-gel techniques starting from alkoxides (Al-butylate, tetraethylorthosilicate) and alkoxides plus nitrates (tetraethylorthosilicate, Al(NO₃)₃·9H₂O). After drying at 150°C the aluminosilicate gels are non-crystalline and remain so up to 900°C. Above 900°C the gels transform into Al₂O₃-rich mullite plus a coexisting SiO₂ phase. Structural studies on temperature-dependent dehydroxylation and condensation of the gels were carried out by large angle X-ray scattering, by infrared spectroscopy and by²⁹ Si NMR spectroscopy. Heat-treatment (<150°C) of dried gels first causes removal of the H₂O and organic residuals weakly bound at the open pore surfaces of the gels while the stronger, structurally bound OH groups are not affected. At temperatures <600°C OH groups are released and recombine to molecular H₂O. If the temperature does not exceed 800°C the newly formed H₂O is trapped in closed nanopores of the gel-network. Corresponding electron microscopical investigations reveal agglomerates of 10 nm sized primary particles virtually unaffected by the heat-treatment below 900°C. NMR investigation provided a new structural model on type and distribution of coordination polyhedra in aluminium silicate gel networks. Unlike Si, which according to ²⁹Si NMR is always 4-fold coordinated with O, ²⁷Al NMR spectroscopy revealed that Al cordination is more complex and is influenced by thermal treatment. Al occurs six-fold (octahedrally) and four-fold (tetrahedrally) coordinated. A third ²⁷Al NMR signal which has been attributed to five-fold-coordinated Al in the literature increased in intensity with the heat-treatment. A comparison of NMR data of the gels with those of mullite suggests that tetrahedra triclusters (3 tetrahedra having one oxygen atom in common) occur as major structural units in aluminium silicate gels rather than five-fold-coordinated Al. Triclusters of tetrahedra may compensate the excess negative charge in the network caused by Si⁴⁺ Al³⁺ substitution. The charge compensation model is supported by aluminosilicate gels doped with network modifiers (e.g., Na⁺). Since equimolar addition of Na⁺ compensates Si⁴⁺ Al³⁺ substitution the formation of triclusters is no longer required which actually can be deduced from²⁷ Al NMR studies.     

SAPO-11分子筛模板剂理论筛选及改进合成

本文通过能学计算,表明二乙胺比二丙胺更有利于合成出高Si含量的SAPO-11分子筛。以二乙胺作模板剂、较高温度水热条件下合成出不同Si/Al比的SAPO-11样品。Si/Al比升高,结晶度下降,晶粒变小。 ²⁹Si NMR谱表明Si/Al比为0.33的SAPO-11的SAPO区明显扩大。     

Synthesis and structures of sila-macrobicyclic compounds: syn and anti isomers of hexasilabicyclo[12.8.8]triacontane

Syn and anti isomers of a novel saturated sila-macrobicyclic compound, hexasilabicyclo[12.8.8]triacontane, were synthesized via the functionalization of 1,1,10,10-tetraphenylhexasilacyclooctadecane derivative, which was obtained by the diimide hydrogenation of the corresponding hexasilacyclooctadecahexayne derivative. The structures of these macrocyclic compounds were determined by ¹H, ¹³C, and²⁹Si NMR and X-ray crystallography.     

MAS-NMR studies of lithium aluminum silicate (LAS) glasses and glass-ceramics having different Li2O/Al2O3 ratio

Emergence of phases in lithium aluminum silicate (LAS) glasses of composition (wt%) xLi₂O-71.7SiO₂-(17.7−x)Al₂O₃-4.9K₂O-3.2B₂O₃-2.5P₂O₅ (5.1≤x≤12.6) upon heat treatment were studied. ²⁹Si, ²⁷Al, ³¹P and ¹¹B MAS-NMR were employed for structural characterization of both LAS glasses and glass-ceramics. In glass samples, Al is found in tetrahedral coordination, while P exists mainly in the form of orthophosphate units. B exists as BO₃ and BO₄ units. ²⁷Al NMR spectra show no change with crystallization, ruling out the presence of any Al containing phase. Contrary to X-ray diffraction studies carried out, ¹¹B (high field 18.8 T) and ²⁹Si NMR spectra clearly indicate the unexpected crystallization of a borosilicate phase (Li,K)BSi₂O₆, whose structure is similar to the aluminosilicate virgilite. Also, lithium disilicate (Li₂Si₂O₅), lithium metasilicate (Li₂SiO₃) and quartz (SiO₂) were identified in the ²⁹Si NMR spectra of the glass-ceramics. ³¹P NMR spectra of the glass-ceramics revealed the presence of Li₃PO₄ and a mixed phase (Li,K)₃PO₄ at low alkali concentrations.     

Nuclear magnetic resonance in the zeolite NaY-hexane system

Conclusions A close interrelationship is found between the,NME spectral data for¹H,¹³C,²³Na,²⁷Al, and²⁹Si and the NMR parameters of the adsorbate and quadrupole nuclei of the adsorbent upon the occupancy of zeolite NaY cavities by hexane molecules.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 185–187, January, 1988.