H. van Koningsveld

On the location and disorder of the tetrapropylammonium (TPA) ion in zeolite ZSM-5 with improved framework accuracy

i11.96/~do.04024 . ½NC12H28OH + nH20 (+0.04Na+?), Mr = 822.65 + (n x 18), orthorhombic, Pnma (assumed), a = 20.022 (2), b = 19.899 (2), c = 13.383 (1) /~, V=5332(4)A 3, Z=8, Dx=2.06 (including TPAOH), Dx = 1.80 gcm -3 (for the anhy- drous framework), h(Mo Ka) =0.71069 A, /z = 6.91 cm -1, F(000) = 3343.7, T = 293 K, R = 0.042 for 4523 observed reflections with l>2.0cr(I). The framework topology agrees with earlier descriptions. Straight channels and sinusoidal channels run parallel to (010) and (100), respectively. The sym- metry of the framework atoms is too close to Pnma to permit refinement in Pn21a. In the straight channel an approximate mirror plane through N and the chan- nel axis, perpendicular to the crystallographic mirror plane, exists. The tetrapropylammonium ion lies at the intersection of the straight and sinusoidal chan- nels in two different orientations. The two orienta- tions, populated in a ratio of 3:2, are nearly related by the approximate mirror plane. Contrary to literature data the propyl-N-propyl fragments point- ing into the sinusoidal and straight channel, respec- tively, both have CNCC torsion angles around 60 °. No evidence is obtained for the tetrapropylam- monium ion breaking the rn symmetry and extra disorder around rn is assumed. The mean C-C and C-N distances and mean CCC, CCN and CNC angles, averaged over both ions, are 1.55 and 1.57 A and 109, 113 and 109 °, respectively. Contact distances smaller than 4.0/~, between terminal C atoms of adjacent template ions, are in the range 3.56 (7)- 3.75 (2) ~.

The monoclinic framework structure of zeolite H-ZSM-5. Comparison with the orthorhombic framework of as-synthesized ZSM-5

The monoclinic framework structure of zeolite H-ZSM-5 (Si 95.68 Al 0.32 H 0.32 O 192 ) has been determined by single crystal X-ray diffraction. The space group is P2 1 /n.1.1. The unit-cell, of dimensions a = 20.107(2), b = 19.879(2), c = 13.369(1)A and α = 90.67(1)°, has 24 independent T sites and Z = 4. The orthorhombic/monoclinic symmetry change, ascribed earlier to a shift of neighboring (010) pentasil layers along c , is realized by a complicated displacement of the framework atoms. The SiOSi angles in the bridges connecting the T 12 -building units into (100) and (010) layers are hardly affected. The transition affects the large SiOSi angles within the T 12 unit most prominently. The corresponding Si O distances are lengthened. The monoclinic framework seems the less strained one. The maximal pore size in the straight channel (∼ 5.8A) is hardly affected by the symmetry change. The sinusoidal cross-sectional area changes from nearly circular (5.3 × 5.6A) in the orthorhombic structure to elliptical in the monoclinic structure (MONO) with major axes of 5.9 and 5.8Ain the two O 10 -rings defining the pore window. In this way the accessibility of the sinusoidal channel in MONO, e.g., for diffusion of p-xylene, is enlarged substantially.

The orthorhombic/monoclinic transition in single crystals of zeolite ZSM-5

Abstract X-ray photographs of single crystals of zeolite H-ZSM-5 (Si 11.96 Al 0.04 H 0.04 O 24 ) at different temperatures are presented. The reversible orthorhombic/monoclinic transition, previously observed with XRD and 29 Si m.a.s. n.m.r. on powder samples of H-ZSM-5, is confirmed. Upon cooling, the orthorhombic H-ZSM-5 single crystal changes into an aggregate of monoclinic twin domains. The directions of a and c in the orthorhombic single crystal and in the monoclinic twinned crystal ( a ≈ 90.5°) are identical. The deviation of α from 90° can be ascribed to a mutual shift of successive (010) pentasil layers along c, induced by a distortion or rotation of the T 4 and T 6 rings interconnecting the layers. The space group of the monoclinic phase most probably is P 1 2 n 11.

Single crystal structure analysis of zeolite H-ZSM-5 loaded with naphthalene

The crystal structure of H-ZSM-5 loaded with 3.68(2) molecules naphthalene per unit cell was solved by single crystal X-ray diffraction. The space group is orthorhombic, Pnma, with a=19.919(1), b=19.955(s) and c=13.357(1) A and V=5309(1) A3. There are eight Si11.96Al0.04O240.46C10H8 (+0.04H+) units per unit cell. Dx=1.959 Mg m−3, γ(MoKα)=0.71069 A and μ(MoKα)=0.677mm−1. The final R(Rw)=0.044 (0.038), w=1σ2(F), for 5605 observed reflections with I>2.0 σ(I) measured at 293 K. The inversion of the a and b unit cell parameters (ab=0.996), first reported by Mentzen et al. [B.F. Mentzen, M. Sacerdote-Peronnet, J.F. Berar and F. Lefebvre, Zeolites, 13 (1993) 485] is confirmed. The straight channel axis along [010] has elliptical cross-sections with limiting apertures of 4.55 × 6.44 A (roxygen=1.35 A). The 10-ring pores in the sinusoidal channel remain almost circular (major and minor axes being about 5.6 and 5.2 A). Naphthalene molecules are located at the channel intersections. Their long molecular axis (parallel to a molecular 2-fold axis) deviates 1.7° from [010]. The angle between the normal on the plane of the molecule and the positive a axis is 40.5(3)°. The naphthalene molecules form loosely connected chains in the straight channel; the shortest non-bonding CC distance between neighbouring molecules in the straight channel is 4.57(2) A.

Preparation and structure of crystals of zeolite H-ZSM-5 loaded with p-nitroaniline

Abstract A crystal of H-ZSM-5 loaded with p -nitroaniline exhibits domains of different symmetry depending on the loading time. At very short loading time, domains with monoclinic P 2 1 / n .1.1 symmetry, with orthorhombic P2 1 2 1 2 1 symmetry and with orthorhombic Pnma symmetry coexist. At very long loading time, crystals containing one type of domain with orthorhombic Pnma symmetry are prepared. At intermediate loading time, orthorhombic domains with P2 1 2 1 2 1 and Pnma symmetry are present. Refinement of the latter type of p -nitroaniline/H-ZSM-5 crystals leads to an apparent improvement in the structural model when the symmetry is lowered during the refinement. The structure of a single-domain crystal of H-ZSM-5, loaded with approximately four p -nitroaniline molecules per unit cell, was solved by single crystal X-ray diffraction in the orthorhombic space group Pnma with a = 19.960(1), b = 19.941(2) and c = 13.367(1) A. The structure contains eight Si 11.96 Al 0.04 O 24 0.5C 6 H 6 N 2 O 2 (+0.04H + ) units per unit cell. The final R(R W ) = 0.050 (0.046), with w =1/ σ 2 ( F ), for 5608 observed reflections with I >1.0 σ(I) measured at 293 K. The refinement results do not justify the conclusion that the crystal structure is better described in the acentric space group Pn 2 1 a . The p -nitroaniline molecules are located at the channel intersections and form loosely connected chains in the straight channel. The deformations of the channel pores are not essentially different from those caused by the adsorption of p -dichlorobenzene or naphthalene: the straight channel pores are strongly elliptically distorted while the sinusoidal channel pores are hardly affected by the adsorption.

The molecular structure of π-(tricarbonylchromium)-toluene

The molecular structure of π-(tricarbonylchromium)toluene, CrC 10 H 8 O 3 , has been determined from three-dimensional X-ray data. The orthorhombic unit-cell, P 2 1 2 1 2 1 with a = 11.109(4), b = 7.231(3) and c = 12.206(4)A, contains four molecules. Refinement converged to a final weighted R -index of 4.1% for 1163 observed reflexions. The orientation of the tricarbonylchromium group is nearly eclipsed with respect to the carbon atoms C(1), C(3) and C(5).

The location of p-dichlorobenzene in a single crystal of zeolite H-ZSM-5 at high sorbate loading

The crystal structure of a high-loaded complex of H-ZSM-5 with eight molecules of p-dichlorobenzene per unit cell has been solved by single-crystal X-ray diffraction. The orthorhombic space group P2 1 2 1 2 1 with a = 20.102 (6), b = 19.797 (9), c = 13.436 (3)A and V = 5347 (3) A 3 has four Si 23.92 Al 0.08 O 48 .2C 6 H 4 Cl 2 units per unit cell. D x = 2.164 M gm -3 , λ(MoKα) = 0.71073 A and μ(MoKα) = 0.876 mm -1 . The final R(wR) = 0.046 (0.039), w = 1/σ 2 (F), for 6090 observed reflections with I >1.0σ(I) measured at 293K. The straight channel parallel to [010] is slightly corrugated. The elliptical cross sections, have limiting apertures of 6.0 x 4.9A (r oxygen =1.35 A). The sinusoidal channel parallel to [100] is elliptical with major and minor axes of 6.1 x 4.8 A, respectively. One of the two independent p-dichlorobenzene molecule lies at the intersection of the straight and sinusoidal channels with its long molecular axis almost parallel to (100) and deviating ∼8° from [010]. The second p-dichlorobenzene molecule is in the sinusoidal channel. Its long molecular axis deviates almost 7° from [100] and is practically parallel to (010). The structural aspects are in all details comparable to those in the high-loaded H-ZSM-5/p-xylene complex [van Koningsveld, Tuinstra, van Bekkum & Jansen (1989). Acta Cryst. B45, 423-431], except for the main interaction forces between the p-dichlorobenzene molecules at the channel intersection.

Single-crystal structure analysis and energy minimizations of a MFI-type zeolite at low p-dichlorobenzene sorbate loading

The crystal structure of a low-loaded adsorption complex of H-ZSM-5 with p-dichlorobenzene has been studied by single-crystal X-ray diffraction. The controversy in the literature, concerning the preferred location of the p-dichlorobenzene molecule, is explained by different interpretations of the difference electron-density map representing the electron density of the absorbed molecule. The crystal studied contains 2.56 (2) p-dichlorobenzene molecules per unit cell. The absorbed molecules prefer the position at the intersection of channels. Energy calculations, using the Biosym Catalysis and Sorption Software, strongly support this interpretation. In nearly all calculations the orientation of the relaxed molecule is close to the orientation found from the X-ray analysis. A second rotational position at the intersection, suggested from calculations in a fully relaxed structure, resembles the location of the p-xylene molecule at the intersection of channels in the high-loaded H-ZSM-5/8p-xylene complex. The unit cell of Si11.96Al0.04O24.0.32C6H4Cl2(+ 0.04H+), Mr = 767.42, is orthorhombic, Pnma, with a = 20.009 (3), b = 19.909 (4), c = 13.366 (2) A, V = 5324 (2) A3, Z = 8, Dx = 1.922 Mg m−3 and μ(Mo Kα) = 0.734 mm−1. The final R(wR) is 0.044 (0.048), w = 1/σ2(F), for 5306 observed reflections with I> 2.0σ(I) measured at 293 K.

Absolute configuration and domain structure of AlPO4-5 studied by single crystal X-ray diffraction

Abstract The absolute configuration of AlPO 4 -5 has been determined from single crystal X-ray diffraction data. The intensities of Friedel related reflections were measured at room temperature from a microcrystal (maximum size ∼50 μm) using synchrotron radiation ( λ =1.46 A) and at 100 K from a larger crystal (∼250 μm) using radiation from a sealed Cu tube ( λ =1.5418 A). Both data sets indicate the same absolute configuration. The Al(O)P vector, parallel to the polar channel axis, points along the main growth direction. Perpendicular to the main growth direction, the crystal is terminated by an Al(O)P plane with the Al atoms at the surface. The crystal structure of AlPO 4 -5, a = b =13.718(1) A, c =8.4526(5) A, and γ =120.00°, is described as consisting of three types of microdomains, each exhibiting P6 symmetry. The domains are related by two sets of glide planes. The average structure has P6cc symmetry. All observed angles and distances are within acceptable limits: P–O=1.50–1.57 A, Al–O=1.69–1.76 A, O–P–O=104–119°, O–Al–O=99–124° and Al–O–P=137–154°. The observed (weak) diffuse scattering might be caused, besides, the disorder of the template molecules, by incoherent scattering of domain walls, which exhibit geometries slightly different from each of the three domains.

Interpretation of 29Si MAS n.m.r. spectra by X-ray data: Application to the monoclinic and orthorhombic framework of zeolite ZSM-5

Abstract The previously established relation between isotropic 29 Si chemical shifts δ and mean SiOSi bond angles α of the form δ = A cosα (cosα − 1) + B is applied to calculate “theoretical” 29 Si n.m.r. spectra of monoclinic ( P2 1 n ) and orthorhombic ( Pnma ) frameworks of zeolite ZSM-5. Mean SiOSi bond angles from recently published single crystal X-ray refinements of improved accuracy are used in the calculations. Good agreement between theoretical and experimental spectra as well as between the bond angles from XRD and those calculated from 29 Si chemical shifts has been found for the monoclinic form of high-silica ZSM-5. The theoretical spectrum of orthorhombic as-synthesized TPA-ZSM-5 cannot be directly compared with the experimental spectrum because of insufficient resolution of the latter. However, the spectral patterns observed for several sorbate loaded ZSM-5 frameworks of orthorhombic symmetry are very similar to the calculated spectrum. The characteristic changes of the 29 Si n.m.r. spectra induced by the transition from monoclinic to orthorhombic symmetry of the ZSM-5 framework are discussed and related to the changes in the local structure of distinct Si sites.