Jürgen Felsche

Phases and phase transitions of compounds (CnH2n+1NH3)2MnCl4 with n = 1, 2, 3

Abstract Phases and structural phase transitions of the compounds (CH 3 NH 3 ) 2 MnCl 4 , (C 2 H 5 NH 3 ) 2 MnCl 4 and (C 3 H 7 NH 3 ) 2 MnCl 4 have been studied by means of thermoanalytical methods (DSC) and X-ray single crystal and powder diffraction data in the temperature range of 85–480°K at normal pressure. All phases show perovskite-like layer structures. The high temperature phases (α phase) correspond to the K 2 NiF 4 type and may be regarded as the aristotype of each polymorphic compound. All transitions are reversible. Transition patterns are: Based on the DSC peak-shape analysis and diffraction data a model of a tilting system of the MnCl 6 -octahedra layer is introduced in order to understand essential features of structures of different phases and their transition behavior. Single crystal film data of (C 3 H 7 NH 3 ) 2 MnCl 4 phases reveal some disorder phenomena. The e phase exhibits a superstructure along [010] with a triplication of the shortest axis corresponding to the δ phase. The γ phase of this compound shows strong satellite reflections, due to a transverse distortion wave along the [100] lattice direction.

29Si MAS n.m.r. of aluminosilicate sodalites: Correlations between chemical shifts and structure parameters

Abstract The 29 Si n.m.r. chemical shifts of 16 sodalites of the general composition M 6+x [SiAlO 4 ] 6 A x ·nH 2 O (M = alkali metal cation, A = OH − , anion) cover a range of more than 20 ppm and show linear correlations with the SiOAl bond angles and the lattice constants. As a result of the different steric and coordination requirements of the various nonframework constituents, bond-angle variations between 126 and 160° occur, and these can be calculated directly from the chemical shift data. The 29 Si chemical shifts and the average SiOAl bond angles of Si(4Al) environments in several other zeolites also fit the same type of correlation that has been established here for the sodalites.

Synthesis, X-ray diffraction, and MAS n.m.r. characteristics of tetrahydroxoborate sodalite, Na8[AlSiO4]6[B(OH)4]2

Abstract Hydrothermal crystallization in the system Na2OSiO2Al2O3B2O3H2O reveals the dominant formation of tetrahydroxoborate sodalite, Na8[AlSiO4]6[B(OH)4]2, in the temperature range of 473–773 K at pressures of 100–150 MPa and concentrations of 17 Na2O:2 SiO2:Al2O3:xB2O3:yH2O (x = 0.1–10; y = 260–290). The high-temperature form (T ≥ 310 K) of tetrahydroxoborate sodalite shows cubic symmetry [space group P 4 3n, a 0 = 9.010(1) A ], whereas the superstructure diffraction pattern of the low-temperature form (T ≦ 270 K) has been indexed successfully by means of transformation of the cubic ∼ 9 A subcell to orthorhombic symmetry with a0 = 25.510(1), b0 = 12.750(1), and c 0 = 9.020(1) A . 29Si MAS n.m.r. shows complete ordering of the Si,Al atoms in the tetrahedral framework of tetrahydroxoborate sodalite. The observed single peak of the 11B MAS n.m.r. spectra correlates with the imbibition of [B(OH)4]− at the center of the sodalite cages. Substitution of B for Al in the tetrahedral sites of the sodalite framework and threefold coordinated boron within the sodalite cages or in the framework can be excluded.

AXES1.9: new tools for estimation of crystallite size and shape by Williamson–Hall analysis

Dialogues for the estimation of crystallite size, shape and lattice strain are designed and included in an X-ray powder diffraction (XRPD) program, named AXES. They implement peak fitting and Voigt analysis followed by a Williamson–Hall plot (WHP). Eight different peak-shape functions can be used for individual peak fitting. Volume-weighted crystallite size and effective lattice deformation are calculated from linear interpolation of the WHP. Actual dimensions (diameters of spheres, diameters and heights of cylinders) are calculated, assuming spherical or cylindrical shapes of the crystallites. Results of size–shape analyses can be visualized in the form of a WHP and as an arrow diagram (HPGL format), which shows distribution of observed apparent and true sizes of crystallites with a diffraction vector. The program has been written in Borland Pascal 7.0 for MS-DOS. The executable code is available via the World Wide Web.

Multinuclear solid state NMR of host-guest systems with TO2 (T=Si, Al) host-frameworks. A case study on sodalites

Abstract The application of high-resolution multinuclear solid state nuclear magnetic resonance (NMR) spectroscopy to the structural characterization of microporous host-guest systems is demonstrated by a series of sodalites with aluminosilicate, aluminate and silicate host-frameworks and a large variety of guest species (inorganic anions and cations, H2O, OH−, organic molecules) enclathrated in the sodalite cages. While 29Si and 27Al NMR provide information on the local structure and composition of the framework, 23Na and 1H HMR give insights into the structure and dynamics of the cage fillings. The number of crystallographically inequivalent Si, Al and Na sites in the sodalite structures is determined from the 29Si, 27Al and 23Na NMR spectra and their local geometry is characterized by detailed interpretation of the isotropic chemical shifts and the 27Al and 23Na quadrupole parameters. Dynamic reorientation processes of the guest species and structural phase transitions of distinct sodalite compositions were studied by multinuclear magic angle spinning (MAS) NMR at variable temperature. Besides MAS NMR, double rotation (DOR) NMR experiments at different field strengths were performed for 27Al and 23Na to resolve strongly overlapping lines of the MAS NMR spectra.

N(nPr)4[B5O6(OH)4][B(OH)3]2 and N(nBu)4[B5O6(OH)4][B(OH)3]2: Clathrates with a diamondoid arrangement of hydrogen-bonded pentaborate anions

Single-crystal X-ray structure analyses of N(nPr)4[B5O6(OH)4][B(OH)3]2,1, and N(nBu)4 [B5O6(OH)4][B(OH)3]2,2, reveal that these materials are novel clathrates, the isotypic host structures of which are three-dimensional assemblies of hydrogen-bonded [B5O6(OH)4]− ionsand B(OH)3 molecules. The assembly of only the pentaborate anions is a distorted (i.e., along [102] elongated) fourconnected diamond-related network. The N(nPr)4+ and N(nBu)4+ ions are trapped within the complex three-dimensional channel systems of the host frameworks. Both1 and2 crystallize monoclinically with space groupP21/c andZ=4. The cell constants are:1:a=13.592(5),b=12.082(2),c=17.355(6) Å, β=106.60(2)° (298K);2:a=13.874(3),b=12.585(1),c=17.588(4) Å, β=107.04(1)° (238 K). The results obtained by both11B and13C MAS NMR spectroscopy are discussed. Thermogravimetric studies under a flowing inert-gas atmosphere suggest that water, stemming from polycondensation of the hydrous borate species, is released from the clathrates at ca. 443 K (1) and 398 K (2) before the decomposition of the organic cations starts at ca. 603 K (1) and 603 K (2).

X-ray powder diffraction crystal structure analysis and 29Si, 23Na MAS n.m.r. studies of nitrite sodalite, Na8[AlSiO4]6 (NO2)2, at 295 K

The crystal structure of nitrite sodalite, Na 8 [AlSiO 4 ] 6 (NO 2 ) 2 [space group P 43 n , a 0 = 893.0(1) pm], has been determined by X-ray powder diffraction data at 295 K. The aluminosilicate framework shows regular bonding with values of Si-O = 162.4(1) pm, Al-O = 174.3(1) pm, and Si-O-Al = 139.23(8)°. The 29 Si MAS n.m.r. chemical shift value of 85.5 ppm verifies the Si(O Al) 4 ordering of the framework constituents. The nitrite anion with the nitrogen atom located at the central position exhibits 12-fold orientational disorder within the [4 6 6 8 ]-sodalite cage. The orientational disorder of the NO 2 − anion also affects the oxygen coordination of the sodium atoms. A considerable degree of dynamics in the oxygen coordination of the sodium atoms is suggested from 23 Na MAS n.m.r. spectra and heating X-ray powder diffraction data

Structural links between zeolite-type and clathrate hydrate-type materials: Redetermination of the crystal structure of [N(CH3)4]8[Si8O20]·65H2O by single-crystal X-ray diffraction and variable-temperature MAS NMR spectroscopy

Abstract The tetramethylammonium silicate hydrate [NMe4]8[Si8O20]·65H2O (1 hereafter) crystallizes triclinically with space group P 1 , Z = 1 and the cell constants a = 15.644(3), b = 15.756(4), c = 15.967(5) A, α = 119.31(2), β = 108.83(2), γ = 91.99(2)° (T = 215 K). It is shown that the polyhydrate is a host—guest compound with a mixed three-dimensional host structure composed of oligomeric [Si8O20]8− anions and H2O molecules linked via hydrogen bonds OH⋯O (heteronetwork clathrate). The silicate anions possess a cube-shaped double four-ring structure. Four distinct large, irregular, cage-like voids house the guest species NMe4+. MAS NMR spectra measured at various temperatures between 170 and 290 K reveal that the 13C resonance of the NMe4+ cation is shifted continuously to higher field with decreasing temperature and depends primarily on the chemical composition of the cage wall rather than on the cage size. At room temperature the 1H MAS NMR spectrum is well resolved, suggesting that both the H2O molecules and NMe4+ cations are highly mobile on the NMR time scale. The water dynamics slow down at temperatures below ca. 250 K which in turn affects the motions of the guest species. The polyhydrate melts incongruently at 345 K with the formation of a liquid phase and a crystalline heteronetwork clathrate, the host structure of which possesses the topology of the zeolite structure type AST.

X-ray absorption spectroscopy of metal atom-substituted microporous materials

Abstract X-ray absorption spectroscopy has been applied to the characterization of metal atom-substituted microporous materials. The two spectral regions of an X-ray absorption spectrum - XANES and EXAFS - provide information about the local coordination environment of the atom investigated. Gallosilicate sodalites are shown to contain Ga in fourfold coordinated framework sites with GaO bond lengths of 1.83(2) A. By contrast, in CoAPO-20, tetrahedrally and octahedrally coordinated Co atoms have been identified. In TS-1, a catalytically active titanium silicate having the structural features of the zeolite ZSM-5, Ti is octahedrally coordinated by oxygen atoms. There are indications that Ti is incorporated into the framework of the zeolitic material.

Synthesis and characterization of two new silica socialites containing ethanolamine or ethylenediamine as guest species: [C2H7NO]2[Si6O12]2 and [C2H8N2]2[Si6O12]2

Two new clathrasils with sodalite structure were obtained using ethanolamine (EA) and ethylenediamine (ED), respectively, as structure-directing agents that also serve as solvents during the synthesis. Crystallization in the systems SiO 2 -Na 2 O-EA and SiO 2 -Na 2 O-ED, respectively, yields silica sodalites with each sodalite cage occupied by the corresponding organic molecule. The EA and ED molecules are the first amines that were found to direct the formation of silica sodalites. The two new silica sodalites were characterized by temperature-dependent powder X-ray diffraction, infrared and n.m.r. spectroscopy ( 1 H, 29 Si, 13 C), thermal analysis, and differential scanning calorimetry. Their properties are discussed and compared with ethylene glycol silica sodalite.