H. Gies

Synthesis and crystal structure of the new borosilicate zeolite RUB-13

Abstract RUB-13 is a borosilicate zeolite which represents a new porous structure type. The material was synthesized in the system SiO 2 B 2 O 3 ethylenediamine-1,2,2,6,6-pentamethylpiperidinewater at 160°C. Single crystal structure analysis ( R =6.0%) revealed that RUB-13 has two-dimensional pore system with intersecting 8-membered ring channels. The void at the intersection is a large [4 6 5 8 6 4 8 4 ] cage with a free volume of ca. 550 a 3 . 13 C Cross-polarization magic-angle spinning nuclear magnetic resonance (CP-MAS NMR) spectroscopy proves that protonated pentamethylpiperidine (PMP) molecules occupy the cages and compensate the negative charge of the borosilicate framework. The unit cell composition is [Si 30.4 B 1.6 O 64 ]·1.6 PMP. All crystals are contact twins with a twin plane (001) and show signs of one-dimensional disorder.

Ordered and disordered pNA molecules in mesoporous MCM-41

Para-nitroaniline (pNA) has been incorporated into the one-dimensional channels of mesoporous MCM-41, the hexagonal member of the M41S family of ordered mesoporous silicate materials. The composite material shows a number of remarkable features, depending on the sorption procedure for the organic component, the after treatment, and the annealing time of the composite. In X-ray diffraction experiments different states of one-dimensional ordering of the sorbate molecules in the channel pores are observed. In agreement with the molecular dipole, chain-like coherent domains with the long axis of the sorbate molecule parallel as well as perpendicular to the host channel axis show up. In aged samples the periodic ordering of the pNA molecules is lost, and nonlinear optical properties of the composite have been measured in second harmonic generation experiments indicating the presence of a polar direction in the sample.

New structures—new insights: Progress in structure analysis of nanoporous materials

In the recent past structure determination of microporous materials has experienced considerable developments in methodology. The FOCUS method: high resolution powder diffraction data used for direct method structure solution in combination with crystal chemistry based modelling. The models are retrieved from electron density maps calculated in direct method runs, energy minimized and checked through for realistic angles and distances values. The SUM-TF method: diffraction patterns at moderate resolution analysed with direct methods using a modified tangent formula which includes Patterson information for the structure solving. In this way the atomic resolution criterion for direct methods is bypassed. This overview gives a summary of the structures successfully solved using these new techniques.

Decasils, a new order-disorder family of microporous silicas

Abstract Decasils are a new order-disorder family of porous structures. All ordered and disordered decasil structures are built from one-dimensional chain-like basic building units that can be connected in different ways. Three simplest ordered framework structures of this family are possible: decasil types A, B, and C. All decasil types possess cage-like voids that share 8MR pore openings to give a one-dimensional channel system. Using two different templates an ordered and a disordered form of the decasil family of structures have been synthesized. RUB-3 (decasil type A) was obtained with exo-2-aminobicyclo[2.2.1.]heptan as template and is ordered; RUB-4 was obtained with 3-azabicyclo[3.2.2]nonane as template and is disordered. The structure of RUB-3, which crystallizes in space group C 2/m (a = 14.039(2)A, b = 13.602(2) A, c = 7.428(1) A, and β = 102.22(3)°), has been solved by model building and simulation of X-ray powder pattern and has been confirmed in a Rietveld analysis.

Quinuclidine derivatives as structure directing agents for the synthesis of boron containing zeolites

n-Alkylquinuclidinium ions with alkyl groups in the range from C 1 to C 6 were synthesized with the purpose of studying their influence as structure directing agents (SDAs) in zeolite synthesis, in particular on the structure type formed. Syntheses were performed in the system SiO 2 –B 2 O 3 –SDA–H 2 O–CH 3 OH under hydrothermal conditions at 160, 180, and 200 °C. B 2 O 3 was added in order to allow for charge balance through partial replacement of silicon atoms by the trivalent atom as established by 11 B MAS NMR spectroscopy. The synthesis experiments led to the formation of seven different structure types: dodecasil 1H (DOH); decadodecasil 3R (DDR), sigma-2 (SGT), RUB-1 (LEV), ZSM-5 (MFI), EU-1 (EUO) and ZSM-12 (MTW) all containing n-alkylquinuclidinium ions as templates. In one case (SGT-type material) the active templating ion, methylquinuclidinium, was formed in situ from quinuclidine and methanol present in the reaction mixture. In order to identify the templating molecules (SDA) in the zeolite host framework solid-state 1 H– 13 C CP MAS NMR was used. A single crystal structure refinement of quinuclidinium–DDR clearly shows the host–guest arrangement inside the zeolite pores.

X-ray powder diffraction and NMR-spectroscopic investigations on a porous zincosilicate related to the zeolite VPI-7 (VSV)

Abstract Structural investigations on a new porous zincosilicate phase, VPI-7#, which is related to VPI-7 were carried out using high resolution X-ray powder diffraction and multinuclear NMR experiments ( 29 Si CP MAS and 23 Na DOR). The combination of these complementary techniques allowed for the identification of VPI-7# and an understanding of the structural differences between VPI-7# and VPI-7. VPI-7# crystallizes in the triclinic space group P1 with cell parameters a = 40.12(2) A , b = 10.296(5) A , c = 10.246(5) A , α = 90.74(2) °, β = 91.66(2) ° and γ = 87.89(2) °. Taking into account the closely related unit cell parameters and the similarity of the chemical shifts of the 29 Si NMR signals in the spectra of VPI-7# and VPI-7 the framework topology of the two zincosilicates is the same. Based on a preliminary Rietveld refinement the Zn-ordering in the zincosilicate framework of VPI-7# is also the same as in VPI-7. 23 Na DOR experiments of VPI-7 and VPI-7# show an increase in the number of symmetrically inequivalent, however, well ordered Na-sites. This leads to the conclusion, that the ordering scheme of the nonframework constituents Na and H 2 O is different. The conclusion is based on experimental facts as well as crystal chemical reasoning since the number of atoms in the asymmetric unit (216 framework atoms in general sites) by far exceeds the potential of a Rietveld analysis.

A tangent formula derived from Patterson-function arguments. III: Structure determination of zeolitic and layered materials from low-resolution powder diffraction data

The viability of solving the structure type of zeolitic and layered materials applying multisolution direct methods to low-resolution (~2.2 A) powder diffraction data is shown. The phases are refined with the tangent formula derived from Patterson-function arguments [Rius (1993). Acta Cryst. A49, 406–409] and the correct phase sets are discriminated with the conventional figures of merit. The two test examples presented are (a) the already known tetragonal zeolite ZSM-11 (space group 1{\bar 4}m2) at 2.3 A resolution and (b) the hitherto unknown layer silicate RUB-15 (Ibam) at 2.2 A resolution. In both cases, the tetrahedral Si units appear as resolved peaks in the Fourier maps computed with the phases of the highest-ranked direct-methods solutions.

Synthesis and characterization of boron containing MCM-41

Publisher Summary MCM-41 is a novel mesoporous material first described by Kresge et al. in 1992. MCM-41 has channel like pores of uniform size that are arranged in a regular hexagonal pattern. The pore diameters are in the range of 25 to 100 A depending on the type of detergent cation used as templates during the synthesis. So far, only the aluminosilicate and the pure silica forms of MCM-41 are largely characterized. The chapter presents the synthesis and general characterization of the boron containing MCM-41 (B-MCM-41).

Synthesis and characterization of the microporous silica phase RUB-3 (RTE)

Abstract RUB-3 (structure type code: RTE) was hydrothermally synthesized at 150–170°C from reaction mixtures of the following composition: 1.0 SiO 2 :1.0–5.3 template:0.0–0.67 LiOH:55.5–111.0 H 2 0. So far, exo-2-aminobicyclo[2.2.1]heptane is the only known structure-directing agent to stabilize RUB-3. RUB-3 crystallizes together with three other microporous materials: nonasil (NON), dodecasil 1H (DOH) and dodecasil 3C (MTN). The use of LiOH not only reduced the crystallization time but also suppressed the formation of the additional phases. X-ray diffraction analysis and 29 Si magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy proved that the RUB-3 materials possess excellent crystallinity and a perfectly ordered structure. Moreover, the NMR spectra revealed that RUB-3 has a four-connected three-dimensional SiO 2 framework that occludes exo-2-aminobicyclo[2.2.1]heptane in the pore system. The SiO 2 framework of RUB-3 is stable up to at least 1000°C. Calcination of the as-synthesized RUB-3, however, needs several days for completion.

High-resolution solid-state 29Si n.m.r. on decadodecasil, a microporous clathrasil

Abstract Decadodecasil-3R, a novel microporous clathrasil, yields a highly resolved 29 Si n.m.r. spectrum; a previously established relation between structure and chemical shift is further confirmed.