The discovery of new zeolite framework types plays an important role in producing new porous materials for applications such as adsorption, catalysis, separation, etc.

Hydrated H-Apophyllite (HH-Apo) and H-carletonite (H-Car) were synthesized at 0 °C by leaching an apophyllite and a carletonite single crystal in a large surplus of 1.2 molar hydrochloric acid. The XRD powder patterns of HH-Apo and H-Car were indexed with space group symmetries of P4/ncc and I4/mcm and lattice parameters of a = 8.4872(2) Å, c = 16.8684(8) Å and a = 13.8972(3) Å, c = 20.4677(21) Å, respectively. The crystal structures were solved based on model building of the structures of the precursors and a physico-chemical characterization. Rietveld structure refinements confirmed the structure models. HH-Apo and H-Car are among the very few crystalline silicic acids whose structures have been determined and confirmed based on a structure refinement. The structure of HH-Apo contains thin silicate monolayers that can be regarded as constructed by rings of interconnected [SiO3OH] tetrahedra which form a puckered silicate layer. A sheet of water molecules is intercalated between the silicate layers. There are no direct hydrogen bonds between the silanol groups, but there are hydrogen bonds of different strengths between the terminal O atoms of the silicate layers and the intercalated water molecules. The 1H MAS NMR spectrum presents a strong signal at 4.9 ppm related to the aforementioned bonds and interactions between the water molecules, as well as a small signal at 22.5 ppm corresponding to an extremely strong hydrogen bond with d(O...O) ≈ 2.2 Å. The structure of H-Car is free of structural water and consists exclusively of microporous silicate double-layers with 4-connected [SiO4] and 3-connected [SiO3OH] tetrahedra in a ratio of 1:1 and a thickness of 9.2 Å. Neighboring layers are connected to each other by medium–strong hydrogen bonds with O...O distances of 2.56 Å. The structure of HH-Apo decays within several hours while H-Car is stable. A topotactic condensation reaction applied to H-Car forms an irregularly condensed silicate which still contains the layers in a distorted form as building blocks.

A silica zeolite (RWZ-1) with a very high framework density (FD) was synthesized from highly crystalline natural layered silicate magadiite, bridging the gap between the two research areas of zeolites and dense silica polymorphs. Magadiite was topotactically converted into a 3D framework through two-step heat treatment. The resulting structure had a 1D micropore system of channel-like cavities with an FD of 22.1 Si atoms/1000 & ANGS;3. This value is higher than those of all other silica zeolites reported so far, approaching those of silica polymorphs (tridymite (22.6) and & alpha;-quartz (26.5)). RWZ-1 is a slight negative thermal expansion material with thermal properties approaching those of dense silica polymorphs. It contributes to the creation of a new field on microporous high-density silica/silicates. Synergistic interactions are expected between the micropores with molecular sieving properties and the dense layer-like building units with different topologies which provide thermal and mechanical stabilities. Between zeolite and silica: A silica zeolite RWZ-1 with a very high framework density (FD) was synthesized through topotactic condensation of natural layered silicate magadiite. Based on the viewpoint of its FD and thermal expansion behavior, RWZ-1 is regarded as a truly intermediate silica material between zeolites and dense silica polymorphs, which can be applicable as a unique catalyst and adsorbent.image

O24Si12, tetragonal, P4(3)2(1)2 (no. 96), a = 7.4462(1) angstrom, c = 8.5838(4) angstrom, V = 475.93(3) angstrom(3), Z = 1, R(F) = 0.037, T = 293 K.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

C 48 H 96 B 6 N 6 O 108 Si 48 , trigonal, R 3 ‾ m $R\overline{3}m$ (no. 166), a = 12.8892(1) Å, c = 22.3058(2) Å, V = 3209.23(4) Å 3 , Z = 1, density = 2.02(2) g·cm −3 , R ( F ) = 0.038, Chi 2 = 2.86, T = 293 K.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Magadiite from Lake Magadi was structurally analyzed based on X-ray powder diffraction data. The idealized chemical composition of magadiite is Na-16[Si112O224(OH)(16)]center dot 64H(2)O per unit cell. The XRD powder diffraction pattern was indexed in orthorhombic symmetry with lattice parameters a(0) = 10.5035(9) angstrom, b(0) = 10.0262(9) angstrom, and c(0) = 61.9608(46) angstrom. The crystal structure was solved from a synthetic magadiite sample in a complex process using 3D electron diffraction combined with model building as presented in an additional paper. A Rietveld refinement of this structure model performed on a magadiite mineral sample in space group F2dd (No. 43) converged to residual values of R-Bragg = 0.031 and R-F = 0.026 confirming the structure model. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and DRIFT spectroscopy further confirmed the structure. The structure of magadiite contains two enantiomorphic silicate layers of, so far, unknown topology. The dense layers exhibit no porosity or micro-channels and have a thickness of 11.5 angstrom (disregarding the van der Waals radii of the terminal O atoms) and possess a silicon Q(4) to Q(3) ratio of 2.5. 16 out of 32 terminal silanol groups are protonated, and the remaining groups compensate for the charge of the hydrated sodium cations. Bands of edge-sharing [Na(H2O)(6/1.5)] octahedra are intercalated between the silicate layers extending along (110) and (110). The water molecules are hydrogen bonded to terminal silanol groups with O center dot center dot center dot O distances of 2.54-2.91 angstrom. The structure of magadiite is slightly disordered, typical for hydrous layer silicates (HLS), which possess only weak interactions between neighboring layers. In this respect, the result of the structure refinement represents a somewhat idealized structure. Nevertheless, the natural magadiite possesses a higher degree of structural order than any synthetic magadiite sample. The structure analysis also revealed the presence of strong intra-layer hydrogen bonds between the terminal O atoms (silanol/siloxy groups), confirmed by H-1 MAS NMR and DRIFT spectroscopy. The surface zone of the silicate layers, as well as the interlayer region containing the [Na(H2O)(6/1.5)] octahedra, are closely related to the structure of Na-RUB-18.

Abstract Magadiite from Lake Magadi was structurally analyzed based on X‑ray powder diffraction data. The idealized chemical composition of magadiite is Na16[Si112O224(OH)16]∙64H2O per unit cell. The XRD powder diffraction pattern was indexed in orthorhombic symmetry with lattice parameters a0 = 10.5035(9) Å, b0 = 10.0262(9) Å, and c0 = 61.9608(46) Å. The crystal structure was solved from a synthetic magadiite sample in a complex process using 3D electron diffraction combined with model building as presented in an additional paper. A Rietveld refinement of this structure model performed on a magadiite mineral sample in space group F2dd (No. 43) converged to residual values of RBragg = 0.031 and RF = 0.026 confirming the structure model. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and DRIFT spectroscopy further confirmed the structure. The structure of magadiite contains two enantiomorphic silicate layers of, so far, unknown topology. The dense layers exhibit no porosity or micro-channels and have a thickness of 11.5 Å (disregarding the van der Waals radii of the terminal O atoms) and possess a silicon Q4 to Q3 ratio of 2.5. 16 out of 32 terminal silanol groups are protonated, and the remaining groups compensate for the charge of the hydrated sodium cations. Bands of edge-sharing [Na(H2O)6/1.5] octahedra are intercalated between the silicate layers extending along (110) and (110). The water molecules are hydrogen bonded to terminal silanol groups with O···O distances of 2.54–2.91 Å. The structure of magadiite is slightly disordered, typical for hydrous layer silicates (HLS), which possess only weak interactions between neighboring layers. In this respect, the result of the structure refinement represents a somewhat idealized structure. Nevertheless, the natural magadiite possesses a higher degree of structural order than any synthetic magadiite sample. The structure analysis also revealed the presence of strong intra-layer hydrogen bonds between the terminal O atoms (silanol/siloxy groups), confirmed by 1H MAS NMR and DRIFT spectroscopy. The surface zone of the silicate layers, as well as the interlayer region containing the [Na(H2O)6/1.5] octahedra, are closely related to the structure of Na-RUB-18.

A synthetic kenyaite sample possessing the chemical composition Na-16[Si160O320(OH)(16)]center dot 64H(2)O per unit cell was structurally analysed using X-ray powder data. The powder pattern was indexed based on space group symmetry Fdd2 (No. 43) with lattice parameters a(0) = 10.080(1) angstrom, b(0) = 79.383(8) angstrom, c(0) = 10.604(1) angstrom. The crystal structure was solved by model building based on the unit cell parameters, the results of a general characterisation of the material and the comparison with the closely related structures of RUB-6, Na-RUB-18 and magadiite. A Rietveld refinement of this structure model converged to residual values of chi(2) = 3.1, R-F = 0.020 and R-Bragg = 0.025, confirming the structure model. Physico-chemical characterisation using solid-state NMR spectroscopy, SEM, TG-DTA, and DRIFT spectroscopy further confirmed the structure. The structure of kenyaite contains thick silicate layers with a thickness of 15.9 angstrom (ignoring the van der Waals radii of the terminal oxygen atoms). The dense layers possess the same topology as the layers of RUB-6, exhibit no porosity and have a silicon Q(4) to Q(3) ratio of 4.0. 16 out of 32 terminal silanol groups are protonated while 16 siloxy groups ( Si-O-) compensate the charge of the sodium cations. RUB-6 and kenyaite differ, however, with respect to the cation intercalated and to the stacking arrangement of layers. Bands of edge-sharing [Na(H2O)(6/1.5)] octahedra are intercalated between the silicate layers extending along [110] and [110]. The equatorial water molecules of the octahedra are hydrogen bonded to terminal silanol groups with O center dot center dot center dot O distances of 2.5 angstrom to 2.6 angstrom. The structure of kenyaite is slightly disordered typical for hydrous layer silicates which possess only weak interactions between neighbouring silicate layers. In this respect, the result of the structure refinement represents a somewhat idealised structure. The structure analysis also revealed the presence of strong intra-layer hydrogen bonds (d(O center dot center dot center dot O) approximate to 2.5 angstrom) between the terminal O atoms (silanol/siloxy groups) confirmed by H-1 MAS NMR spectroscopy. The surface zone of the silicate layers as well as the inter-layer region containing the edge-sharing [Na(H2O)(6/1.5)] octahedra are closely related to the structures of Na-RUB-18 and magadiite.

Zeolite materials of the MFI-structure type have been synthesized with tetrapropylammonium (TPA(+)) as organic structure directing agent, (i) applying the all-silica route ((TPA)[Si-MFI-type]), (ii) with fluoride as mineralizer ((TPA,F)[Si-MFI-type]) and (iii) including a boron source ((TPA)[B,Si-MFI-type]). These three materials served as models for different states of defect and perfect framework zeolites in their as-made and calcined states. The materials themselves and their silanol/siloxy type defects were characterized using PXRD, TG/DTA, SS-NMR and IR spectroscopy, i.e. techniques probing long range order and local structure. The combination of these analytical techniques proved to be very helpful for a most complete understanding of their local structure as well as the changes that occur upon heating. If defects were detected, the curability was analysed by performing calcination. Whereas the as-made (TPA,F)[Si-MFI-type] already exhibits a perfect, defect-free silica framework, (TPA)[B,Si-MFI-type] and (TPA)[Si-MFI-type] both show a substantial concentration of defects after synthesis. (TPA)[Si-MFI-type] contains predominantly a complex local defect structure, which is completely curable during calcination. The defects for (TPA)[B,Si-MFI-type]-calc but remained, to a small degree, after calcination and deboronation in (TPA)[B,Si-MFI-type]-deb, where silanol nests had formed intermediately. An IR band at 3730 cm(-1) characteristic for isolated Si-OH indicates that some silanol defects remained due to imperfect condensation of the silanol nests.