Karl G. Strohmaier

Structure of a Three-Dimensional, Microporous Molybdenum Phosphate with Large Cavities

The synthesis, single-crystal x-ray structural characterization, and sorption properties of a microporous molybdenum phosphate, (Me4N)1.3(H3O)0.7[Mo4O8(PO4)2] � 2H2O (Me, methyl), are presented. The three-dimensional framework is built up from Mo4O84+ cubes and PO43- tetrahedra that are connected in such a way that large, cation-filled voids are generated; these voids constitute 25% of the volume of the solid. Absorption isotherms for water show the completely reversible uptake of 4 to 5 percent by weight water into the micropores of this compound, which corresponds to 10 to 12 percent by volume.

A zeolitic structure (ITQ-34) with connected 9- and 10-ring channels obtained with phosphonium cations as structure directing agents.

Zeolites are materials with a large applied interest. Here we present ITQ-34 a new zeolitic material, obtained combining the use of the highly stable tetraalkylphosphonium cations as structure directing agents with the incorporation of Ge atoms in the structure.

EMM-23 : A Stable High-Silica Multidimensional Zeolite with Extra-Large Trilobe-Shaped Channels.

Stable, multidimensional, and extra-large pore zeolites are desirable by industry for catalysis and separation of bulky molecules. Here we report EMM-23, the first stable, three-dimensional extra-large pore aluminosilicate zeolite. The structure of EMM-23 was determined from submicron-sized crystals by combining electron crystallography, solid-state nuclear magnetic resonance (NMR), and powder X-ray diffraction. The framework contains highly unusual trilobe-shaped pores that are bound by 21-24 tetrahedral atoms. These extra-large pores are intersected perpendicularly by a two-dimensional 10-ring channel system. Unlike most ideal zeolite frameworks that have tetrahedral sites with four next-nearest tetrahedral neighbors (Q(4) species), this unusual zeolite possesses a high density of Q(2) and Q(3) silicon species. It is the first zeolite prepared directly with Q(2) species that are intrinsic to the framework. EMM-23 is stable after calcination at 540 °C. The formation of this highly interrupted structure is facilitated by the high density of extra framework positive charge introduced by the dicationic structure directing agent.

Studies of Fe(III) incorporated into AlPO4‐20 by X‐ and W‐band EPR spectroscopies

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

A synchroton single crystal X-ray structure determination of (NH4)3Mo4P3O16: A microporous molybdenum phosphate with Mo4O6+4 cubes

Abstract Reaction of MoO3, Mo, (NH4)2HPO4, H3PO4, and H2O in a mole ratio of 1.4:1:3.6:6:120 at 360°C for 16 hr gives a nearly quantitative yield of black cubes of (NH4)3Mo4P3O16 (1). The structure of (1) was solved from data collected on a 30 × 30 × 30 μm3 crystal at the National Synchrotron Light Source at Brookhaven National Laboratory. The compound is cubic, space group P 4 3m , with a = 7.736(2) A, and was refined to residuals of R(Rw) = 0.035(0.049). Phosphate (1) is isotypic with Cs3Mo4P3O16 and is related to the iron arsenate mineral pharmacosiderite. Unlike the Cs+ compound, (1) can be rendered microporous by thermal removal of the NH+4 cations to give ammonia with the charge compensating proton remaining behind in the lattice. Water absorption isotherms show the reversible uptake of 5.6 wt% water, which corresponds to over 15 vol% void space in (1) after the NH3 removal. The framework consists of Mo4O6+4 cubes, with six MoMo contacts of 2.570(4) A, joined together together by ( PO 4 ) 6 2 along 〈100〉 to form a 3-D network composed of tetramers of triply edge-sharing Mo-centered octahedra and phosphate groups alternating along all 〈100〉 directions. The windows and cavities in (1) are large enough that the NH+4 cations occupy several different positions in the unit cell.

A synchrotron single crystal X-ray structure determination of a small crystal: MoMo double bonds in the 3-D microporous molybdenum phosphate NH4[Mo2P2O10] · H2O

Abstract Black crystals of NH 4 [Mo 2 P 2 O 10 ] · H 2 O, ( 1 ), can be isolated by reacting MoO 3 , Mo, (NH 4 ) 2 HPO 4 , H 3 PO 4 , and H 2 O in a mole ratio of 3:1.1:2:4:120 for 16 hr at 360°C. The structure of phosphate ( 1 ) was determined and refined from single crystal data collected on a 35 × 20 × 10 μm 3 crystal at beamline X10A at NSLS, Brookhaven National Laboratory. Compound ( 1 ) is monoclinic, space group P2 1 n with a = 9.780(10), b = 9.681(5), c = 9.884(8) A, β = 102.17(8)°, V = 915(1) A 3 and R ( R w ) = 0.029(0.024) and contains MoO 6 octahedra and PO 4 tetrahedra. The structure is built up from Mo 4 oxo units that have two edge-sharing Mo 4+ O 6 octahedra that contain MoMo double bonds (2.453(2) A), with the same two oxygens that bridge the Mo 4+ also serving as a corner for two additional Mo 5+ O 6 octahedra. The Mo 4 units are connected by phosphate groups into a 3-D array which generates several types of tunnel which are filled with NH + 4 cations and H 2 O. The material is isotypic with the mineral leucophosphite, K[Fe 2 (OH)(H 2 O)(PO 4 ) 2 ] · H 2 O. Water absorption isotherms show that ( 1 ) is microporous and has about 10–12 vol% internal void space that can be filled by water.

Structure of an Aluminophosphate EMM-8: a Multi-Technique Approach

The crystal structure of an aluminophosphate, EMM-8 (ExxonMobil Material #8), was determined in its calcined, anhydrous form from synchrotron powder diffraction data using the computer program FOCUS. A linkage of double four-ring (D4R) building units forms a two-dimensional framework with 12-MR and 8-MR channels, and differs from a similar SAPO-40 (AFR) framework only by the relationship between paired D4R units. Rietveld refinement reveals a fit of the model to the observed synchrotron data by Rwp=0.1118, R(F2)=0.1769. Local environments of the tetrahedral phosphorus and aluminium sites were established by solid-state NMR, which detects distinct differences between as-synthesized and calcined materials. Distinct, reversible changes in the local symmetry of the P and Al atoms were observed by NMR upon calcination and subsequent hydration. These NMR data provided important constraints on the number of tetrahedral (T) atoms per unit cell and the connectivities of the T atoms. Detailed local structural information obtained by solid-state NMR thereby guided the ultimate determination of the structure of AlPO EMM-8 from the powder data. Comparisons are made to the recently published crystal structure of the fluoride-containing, as-synthesized SSZ-51, indicating that the unit-cell symmetry, axial dimensions and framework structure are preserved after calcination.

Synthesis and structure of ECR-40: An ordered sapo having the MEI framework

Abstract The structure of the silicoaluminophosphate ECR-40 has been determined and refined from synchrotron powder X-ray diffraction data. Its framework is the same as the aluminosilicate ZSM-18, which has the MEI structure. ECR-40 is the first example of a MEI structure with a non-aluminosilicate composition. Due to unique ordering of the silicon, phosphorous, and aluminum atoms into specific T-atom positions, ECR-40 contains odd-numbered rings, which are not present in other tetrahedral SAPO frameworks. 1H, 27Al, 31P, and 29Si MAS NMR data are consistent with the MEI structure. The structure also contains an Al-O-Al connection which imparts very strong acidity to the material.

The crystal structures of polymorphic SUZ-4

Abstract SUZ-4 is an aluminosilicate zeolite originally synthesized at British Petroleum and known to be related somehow to ferrierite. Although a model had been suggested for the framework structure no quantitative proof of its existence has been given in previous work. It is now found to be polymorphic. The originally identified ambient, hydrated form crystallizes in space group Imma where a = 18.882(1), b = 14.872(1), c = 14.211(1) Å. A model constructed by trial and error refines by Rietveld methods to give Rwp = 0.1643, R(F2) = 0.1665. Powder data collected at 100 °C, on the other hand, correspond to the Cmmm model proposed earlier by Lawton et al., where a = 18.790(1), b = 14.2305(8), c = 7.4511(4) Å. The Rietveld match gives Rwp = 0.1473, R(F2) = 0.1508. Although the two forms crystallize in different space groups, the framework topology remains the same, as revealed by vertex symbols and coordination sequences. Evidence is seen for potassium ions that cannot be completely removed by ammonium exchange. Later, the origin of the polymorphic change was discovered to be hydration of microporous channels rather than a thermal effect. Solid-state NMR measurements of the hydrated and anhydrous forms show that a more symmetric environment around the Al species is observed without affecting the coordination of the Al sites. Synchrotron powder data collected at room temperature from anhydrous material conformed to the Cmmm structural model, where a = 18.8064(4), b = 14.2298(3), c = 7.4548(2) Å. Rietveld refinement, including three potassium sites gives Rwp = 0.1127, R(F2) = 0.1296. (Elemental analysis indicates a stoichiometric assembly: K4T36O72; the Rietveld refinement finds 3.86 of the 4.00 potassium atoms.) The material represents a one-dimensional 10-membered ring framework.

The structure of zeolite ZSM-20: mixed cubic and hexagonal stackings of faujasite sheets

Zeolite ZSM-20 comprises faulted block intergrowths of cubic and hexagonal stackings of faujasite sheets, providing a first authentic example of regions of this hexagonal faujasite variant.