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The incorporation of low levels of Mn(II) (Mn/Al~0.001) into five aluminophosphate zeotypes was studied by high-field echo-detected EPR, and by ³¹P and ¹H electron−nuclear double resonance (ENDOR) spectroscopies. The zeotype structures investigated&sbd;SOD, AEL, AFI, SBS, and SBT&sbd;cover a variety of channel morphologies, and span a range of framework densities. The highly resolved EPR spectra could distinguish between two types of Mn with different ⁵⁵Mn hyperfine couplings in structures containing more than one T site. Mims and Davies ³¹P ENDOR spectra, recorded at a field set to one of the |−¹/2, mI〉 → |+¹/2, mI〉 ⁵⁵Mn hyperfine components consist of a symmetric doublet, with a splitting in the range of 5−8 MHz. The large open structures showed smaller couplings than the denser morphologies. A similar ³¹P hyperfine was also detected for Fe(III) incorporated into aluminophosphate zeotype with the SOD structure. Variations in the ¹H ENDOR spectra of the various Mn(II) substituted zeotypes, particularly in the relative intensity of the ¹H matrix line, were detected as well. These ENDOR results indicate a common mechanism of framework substitution in which Mn(II) and Fe(III) are replacing Al (or Mg). Moreover, the spectra serve as a probe for the differences in the local environment and bonding topology of these substituted framework sites. A qualitative interpretation of the ³¹P ENDOR data is provided, based on relevant crystallographic information, and the ¹H ENDOR signals are partially attributed to the interactions with the templates occluded in the zeotype cages. To further relate the isotropic ³¹P hyperfine couplings to structural properties, DFT methods were employed for cluster model optimizations and hyperfine coupling constants calculations. Geometry optimizations of substituted rings, derived from the SOD and AEL framework structures, indicate considerable distortions of the coordination environment of framework Mn as compared to Al. A systematic study of the hyperfine interactions of a series of model structures containing tetrahedral and octahedral Mn(II) show that both Mn−O bond lengths and Mn−O−P bond angles contribute significantly to the variation in the isotropic and anisotropic ³¹P hyperfine coupling.

A combination of continuous wave (CW) electron paramagnetic resonance (EPR), pulsed EPR, and pulsed electron−nuclear double resonance (ENDOR) techniques were used to obtain structural information about the Cu²⁺ ions in hydrated, room-temperature evacuated, and dehydrated Cu−Y (Si:Al = 12 and 5) with a particular emphasis on framework Al interactions. W-band ¹H ENDOR was used to probe the water ligands, whereas X-band hyperfine sublevel correlation (HYSCORE) spectroscopic measurements were employed to detect ²⁷Al hyperfine couplings. The X-band CW EPR spectra show that a total of three Cu²⁺ species (A, B, and C) are present in the samples. ENDOR measurements of hydrated and evacuated Cu−Y-12 indicate that species A and B have a complete coordination sphere of water and, on the basis of the absence of ²⁷Al signals in the HYSCORE spectrum, the Cu²⁺ is not directly bonded to the zeolite framework. Evacuation converted species B to species A. ¹H ENDOR spectra combined with simulations show that upon freezing, the equatorial and axial water ligands of species A and B have a distribution of orientations with respect to the Cu−O bond. The CW EPR spectrum of dehydrated Cu−Y-12 shows a single species (species C) and the HYSCORE spectrum exhibits cross-peaks from ²⁷Al with an isotropic coupling, aiso, of 1.5 MHz. Unlike Cu−Y-12, evacuated Cu−Y-5 consists of species A and C, and the HYSCORE spectrum clearly shows a doublet of ²⁷Al cross-peaks with aiso = 3.0 MHz assigned to species C. Upon dehydration, the ²⁷Al coupling decreases to 2.6 MHz. This indicates that in species C the Cu²⁺ is bound to framework oxygens which are bonded to an Al nucleus. For Si:Al = 5, the zeolite framework becomes negative enough that it can replace water ligands even after mild evacuation. Simulations of ²⁷Al HYSCORE spectra indicate that species C is Cu²⁺ bound to the framework oxygens primarily near a single Al nucleus with a large quadrupole coupling constant.

The incorporation of Fe(III), during the synthesis, into aluminosilicate sodalite (FeSOD) and aluminophosphate sodalite, AlPO4-20 (FAPO), was investigated by continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) techniques at X- and W-band. Specifically, the effect of the framework composition and the presence of occluded template molecules (tetramethyl ammonium hydroxide, TMAOH) in the β cages on the distribution of the Fe(III) species was explored. The X-band CW EPR spectrum of FAPO shows the existence of two types of species, one with a large (g ≈ 6.3,4) and the other with a small (g ≈ 2) zero field splitting (ZFS) interaction. These species were also found in FeSOD synthesized with TMAOH. The X-band field-sweep echo-detected (FS-ED) EPR spectrum shows contributions only from the Fe(III) species in the more symmetric environment (g ≈ 2). The other was not detected due to fast relaxation. This spectrum is very broad and suffers from distortions due to the nuclear modulation effect. In contrast, the W-band FS-ED EPR spectrum of the same species was significantly narrower and free from distortions. Analysis of the temperature dependence of the width and relative intensity of the peak corresponding to the |−½ 〉 → | +½ 〉 EPR transition shows that the g ≈ 2 signal arises from a number of Fe(III) species with a distribution of ZFS parameters. Calcination significantly reduces the ZFS parameter, D, suggesting that the distortions of the T sites are due to specific interactions with the template. Electron spin echo envelope modulation (ESEEM) experiments shows the presence of weak dipolar interaction between Fe(III) and template ¹⁴N and ¹H template nuclei, as well as framework ²⁷Al and ³¹P nuclei. This indicates that the species characterized by small ZFS are well dispersed and are located within the inner structure of the zeolite. These g≈ 2 species are most probably Fe(III) in framework sites. A small fraction that occupies highly asymmetric sites (g ≈ 6.3,4), situated at ‘defect’ framework or extraframework sites, and some Fe(II) produced due to the reduction of Fe(III) by the organic template (detected by Mössbauer spectroscopy), were found as well. The possible presence of some extraframework Fe(III) with a g ≈ 2 signal cannot be excluded. Copyright © 1999 John Wiley & Sons, Ltd.

The brightness of synchrotron X-ray sources, which exceeds that available from conventional generators by many orders of magnitude1–3, provides the possibility of making conventional measurements on much smaller samples. We describe here measurements of Bragg diffracted intensities from two microcrystals of cancrinite, a typical zeolite, performed in order to assess the scope of microcrystal diffraction. Our results demonstrate that many materials previously regarded as polycrystalline can now be studied using well established single-crystal methods at synchrotron facilities.

Zeolites dominate petroleum and new petrochemical processing, and any new large-pore zeolite is of major significance. Here we propose a structure for the recently synthesized zeolite phase ECR-1 (ref. 1). The proposed model is an intimate twin of the mordenite2and mazzite3structures, constructed by interposing layers of mordenite-like sheets between layers of mazzite-like cages. Although there is an ambiguity between two ways the layers are interconnected, this layer-twin model explains the results of sorption and crystallization experiments, the spectroscopic data, X-ray and electron diffraction, and high-resolution transmission electron microscopy (HRTEM) lattice imaging results. The ECR-1 channel system is one-dimensional, with 12-membered-ring openings intermediate in size between those of the parent materials. The structure solution confirms the power of HRTEM lattice imaging in helping to solve the structures of microcrystalline materials4,5, and the intergrowth of ECR-1 and mazzite observed in the images suggests that a new subfamily of zeolite materials based on differing sequences of the two structural layers can be synthesized.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Inelastic neutron scattering has been used to measure tetramethylammonium (TMA) template torsional vibrations, vibrations that prove to be sensitive to the strength of the interaction between the template cation and the enclosing zeolite cage.

The structures of the three faujasite framework zeolites NaxGaxSi192‐xO384 with x = 85 (type X), x = 72 (XY), and x = 57 (Y) are satisfactorily described in the space group Fd3m, indicating no long‐range order of Si and Ga.