Space Group Fm3c Research Articles

Symmetry and topology codes of cluster self-assembly for icosahedral structures of the NaZn13-cF112 and TRB66-cF1944 family

Algorithms for combinatorial topology analysis have been developed that allow restoring symmetry and topology codes (program) of crystal structure cluster self-assembly for intermetallic systems. The analysis method is based on the determination of the chemical composition and structure of an intermetallic cluster-precursor and the construction of a basic 3D net of the structure in the form of a graph with the nodes corresponding to the positions of the centers of gravity of the cluster-precursors. The cluster self-assembly of icosahedral structures was modeled for the family of NaZn13-cF112 and TRB66-cF1944 structures, in which the unit cubic cF-cells contain 112 atoms (8 · NaZn13, V = 1849 A3) and 1608 atoms (24 · YB66, V = 23440 A3), respectively. The topological type of the basic 3D net in the NaZn13 and TRB66 structures (with space group Fm-3c) corresponds to the primitive 3D net P c (Pm–3m, cP1) with c.n. = 6. The cluster-precursor of the NaZn13 structure is an icosahedral cluster Zn@Zn12. The cluster-precursor of the TRB66 structure containing 156 B atoms comprises 13 icosahedrons (B12)13, with the icosahedron B12 in the center of the supracluster linked to the 12 icosahedrons forming an icosahedral shell. The Zn13 and (B12)13B cluster-precursors occupy positions 8b in the crystal structures with the highest crystallographically possible symmetry of m3. The symmetry and topology code of the processes of self-assembly of 3D structures from the nanocluster-precursors—primary chain → microlayer → micronetwork—has been completely reconstructed. The large metal atoms A (with c.n. = 24) are spacers in the AZn13 structures, which occupy voids in the 3D nets from the Be13, Co13, Cu13, Zn13, and Cd13 icosahedrons. The atoms spacers in the TRB66 structures (3 TR and 39 B, TR = Y, Sm, Gd–Lu) statistically occupy the large voids in the 3D nets. The TRB66 crystal structure can be obtained from the NaZn13 by the replacement (decoration) of all 13 Zn atoms with 13 icosahedral B12 clusters; and the system of bonds between the structural units is completely conserved in the process.

Crystal structure and morphology of fully hydrated zeolite Na-A

Zeolite Na-A with idealized composition usually stated as Na12Al12Si12O48 · 27 H2O was synthesized with various amounts of triethanolamine (TEA) between 0.25 and 2.5 mol/L, and constant amounts of sodium, silicon, aluminum, and water. The maximum crystal size increased from 9 to 28 μm with decreasing lattice parameters upon increasing amounts of TEA in the initial gel. Crystals synthesized with low amounts of TEA exhibit both {100} and {110} crystal forms while the bigger crystals made with high amounts of TEA are cubes with {100} faces only. The crystal structure of fully hydrated zeolite A, Na94Al94Si98O384 · n H2O (unit-cell composition, n refined to 243 compared with about 216 expected for the type material). was investigated by single-crystal synchrotron methods (space group Fm-3c, a = 24.550(3) Å, room temperature, R1 = 0.071) yielding a very regular framework geometry with Si—O distances between 1.599(1) Å and 1.611(1) Å, and Al—O distances between 1.719(1) Å and 1.737(1) Å. Water molecules form a sodalite-cage-like cluster in the big grc units (α cages). Other water molecules occupy a 48-fold position in the toc units (β cages). Na atoms are close to the centers of the 6-rings and in the grc units of the centers of the 8-rings.

Ionothermal Synthesis of an Aluminophosphate Molecular Sieve with 20‐Ring Pore Openings

Crystalline porous materials with large or extralarge pores continue to be of particular significance in both industry and academia for their potential applications in shape-selective catalysis and adsorption/separation. Of these zeolitic materials, especially aluminosilicateand aluminophosphate-based molecular sieves are of prime interest because of their high stability associated with their widespread use in many established process and emerging applications. The materials VPI-5 (VFI framework type, 18-ring) and UTD-1 (DON framework type, 14-ring) were the first extra-large pore (pores constructed of more than 12 Tatoms) aluminophosphate and aluminosilicate materials discovered. The oxide frameworks are built up by corner-sharing [AlO4] and [PO4] tetrahedra as well as [AlO4] and [SiO4] tetrahedra. In the search for materials with even larger pores, an anionic open-framework aluminophosphate JDF-20 (20-ring) was reported; however, it could not be classified as a zeolite because its framework (with an Al/P ratio of 5:6) is unstable upon removal of the occluded protonated templates by calcination. Larger pore openings were also achieved using Ge or Ga as the framework Tatom in a high amount, for example in ECR-34 (ETR framework type, 18-ring), ITQ-33 (18-ring), cloverite (-CLO framework type, 20ring), and ITQ-37 (30-ring). In this context, the use of Ge or Ga as framework atoms as well as fluoride has been found to facilitate the formation of a double four-ring (D4R) unit. This is in agreement with the prediction by Brunner and Meier that structures with extra-large pores should contain a large number of threeand four-membered rings. Ionothermal synthesis, in which ionic liquids act as both the solvent and template, is a novel method that has attracted great interest in the synthesis of zeolitic and other porous materials. Besides the advantage of experimenting at ambient pressure, ionic liquids offer different chemistry and structural variety associated with the use of additional amines as structure-directing agents (SDA), and therefore open up new vistas for the synthesis of new porous materials. Herein, we report the ionothermal synthesis of the first aluminophosphate molecular sieve with 20-ring pore openings, denoted as DNL-1 (Dalian National Laboratory Number 1). This molecular sieve was confirmed as a structural analogue to the gallophosphate molecular sieve cloverite by using a combination of Rietveld refinement of powder X-ray diffraction (PXRD) data and NMR analysis. Moreover, in comparison to cloverite, DNL-1, as-synthesized and calcined, exhibits excellent stability. DNL-1 was synthesized in the ionic liquid 1-ethyl-3methylimidazolate bromide ([emim]Br) with 1,6-hexanediamine (HDA) as the co-SDA. The detailed synthetic procedure is described in the Experimental Section. The assynthesized DNL-1 material displays uniformly globular agglomerates of grainlike nanocrystals with a diameter of about 20 mm (see the Supporting Information). Analysis by energy dispersive X-ray spectroscopy (EDX) indicates the P/ Al/F molar ratio of approximately 3:3:1. The inductively coupled plasma (ICP) analysis gives the content (wt%) of Al 16.50 and P 16.65. The elemental and thermogravimetric (TG) analyses show the content (wt%) of C 9.72, N 3.64, H 3.29, and a total weight loss of 34%. Combined with the results of the structure refinement (see below), the chemical formula of DNL-1 was determined as j (C6N2H18)104(C6N2H11)80(H2O)910 j [Al768P768O2976(OH)192F288]. Using the initial structure model from cloverite, the Rietveld refinement of as-synthesized DNL-1 was successfully performed in space group Fm 3c with refined unit cell parameter a= 51.363(1) , which is comparable to that of cloverite a= 51.713 , considering the smaller ionic radius of Al. Similar results were observed in the all-silica and Gecontaining polymorph C of zeolite Beta. Figure 1 shows the very good agreement between observed and calculated PXRDpatterns, taking into account the limited signal to noise ratio, in particular for the data collected at a high angle which can be reflected from the expected R factor of 14.5%. These results adequately confirm that DNL-1 is a pure aluminophosphate analogue of the -CLO structure. The skeletal model of the refined framework structure is shown in Figure 2. The framework of DNL-1 shows the general features of the -CLO structure: 1) two nonintersecting three-dimensional channel systems with 20-ring and 8-ring windows, respectively, 2) four terminal hydroxy groups (Al [*] Y. Wei, Prof. Z. Tian, R. Xu, Dr. H. Ma, R. Pei, Prof. W. Zhang, Prof. Y. Xu, Dr. L. Wang, K. Li, Dr. B. Wang, G. Wen, Prof. L. Lin State Key Laboratory of Catalysis Dalian National Laboratory for Clean Energy Dalian Institute of Chemical Physics Chinese Academy of Sciences, Dalian 116023 (China) Fax: (+86)411-843-79151 E-mail: tianz@dicp.ac.cn

Superlattice Formation in Binary Mixtures of Block Copolymer Micelles

Two distinct diblock copolymers, poly(styrene-b-isoprene) (SI) and poly(styrene-b-dimethylsiloxane) (SD), were codissolved at various concentrations in the polystyrene selective solvent diethyl phthalate. Two SI diblocks, with block molar masses of 12,000-33,000 and 30,000-33,000, and two SD diblocks, with block molar masses of 19,000-6000 and 16,000-9000, were employed. The size ratio of the smaller SD micelles (S) to the larger SI micelles (L) varied from approximately 0.5 to 0.6, based on hydrodynamic radii determined by dynamic light scattering on dilute solutions containing only one polymer component. Due to incompatibility between the polyisoprene and polydimethylsiloxane blocks, a binary mixture of distinct SI and SD micelles was formed in each mixed solution, as confirmed by cryogenic transmission electron microscopy. When the total concentration of polymer was increased to 20-30%, the micelles adopted a superlattice structure. Small angle X-ray scattering revealed the lattice to be the full LS13 superlattice (space group Fm3c) in all cases, with unit cell dimensions in excess of 145 nm. A coexistent face-centered cubic phase composed of SD micelles was also observed when the number ratio of S to L micelles was large.

Theoretical study of phase forming of NaZn13-type rare-earth intermetallics

By using the interatomic pair potential obtained with the lattice inversion method,the stability of RT13−xMx (R = La, Ce, Pr and Nd; T = Co and Fe; M = Si, Al, Cr, V andTi) of the NaZn13 type and its derivative structure are studied. The structuraltransition of LaT13−xSix (T = Co and Fe) between the cubic one with the space groupFm3c and the tetragonalone with I4/mcmis imitated from the viewpoint of energy. As for the function of the third elements,Al and Si are beneficial to the phase stability of RT13−xMx, whereas Cr, Tiand V are unfavourable to the stability. In the calculation, the range ofx,with which RT13−xMx could crystallize in the cubic or tetragonal structures,agrees with the experiments very well. The calculated crystallographic parameterscoincide with the experimental observation. In the cubic structure, Si and Alprefer the 96i site, and in the tetragonal structure Si first occupy the 16l(2) site,then the 16k site. In addition, all the site positions of the compounds with eitherthe cubic or tetragonal structure are really congruent with the experimental one.

Structural Study of Sodium-Type Zeolite LTA by Combination of Rietveld and Maximum-Entropy Methods

The electron-density distribution in hydrated and dehydrated sodium-type zeolite LTA was visualized from X-ray powder diffraction data by combining Rietveld analysis and a maximum-entropy method. The X-ray diffraction data were analyzed on the basis of the composition Na95Si97Al95O384 and a structural model (space group Fm3c) obtained by the Rietveld refinement of time-of-flight neutron powder diffraction data for the dehydrated sample. Weighted R factors, wRF, resulting from the analysis by the maximum-entropy method reached 1.15% for the hydrated sample and 0.99% for the dehydrated one. The number of water molecules per unit cell in the hydrated sample was estimated to be ca. 255 by electron-density analysis, agreeing well with ca. 248 determined by thermogravimetry. Adsorbed water molecules are situated beside Na+ ions in electron-density maps. In contrast with the dehydrated sample, Na+ ions in eight-membered rings were moved a little by introducing water into the α-cages.

Microstructure in rapidly solidified Al [sbnd]Ti [sbnd]Ni alloys

Rapidly quenched Al Ti Ni alloys, with total solute concentrations of 5–20 wt%, have been produced in thin ribbon form (30–50 μm thickness) by controlled-atmosphere chili block melt spinning and the resulting microstructures have been characterised using analytical transmission electron microscopy. As-solidified microstructure of alloys, with a Ti:Ni weight ratio in the range 3:1–4:1, invariably contained a uniform, fine-scale dispersion of cuboidal particles of a novel metastable face-centred cubic phase (space group Fm3c, a c = 2.42 ± 0.01 nm), with a composition of approximately 83.1 ± 1.0 at.%Al−12.6 ± 0.5 at.%Ti−4.3 ± 0.5 at.%Ni. In addition, particles of a metastable, primitive orthorhombic phase ( a o = 1.80 ± 0.05 nm, b o = 1.40 ± 0.05 nm, c o = 2.20 ± 0.05 nm) were also detected in a rapidly quenched Al 4Ti 1Ni alloy. The ternary intermetallic particles appeared to form directly from the melt as primary phase during rapid solidification, and their volume fraction increased with increasing total solute concentration. As a result of the high quench rates and large undercooling achieved during solidification, up to 2.5 wt% Ti was retained in rapidly solidified α-Al solid solution. For a total solute concentration of 5 wt%, a decrease in Ti:Ni ratio led to the formation of rapidly solidified microstructures comprising an increasing fraction of spheroidal intermetallic particles of the equilibrium Al 3Ni and metastable Al 9Ni 2 phases, which again appeared to form directly from the melt as a result of micro-cellular solidification.

Neutron diffraction investigation of Si site preference in RENi 10Si 2 compounds

High resolution time-of-flight neutron powder diffraction has been performed on the intermetallic compound YNi 10Si 2 of the ThMn 12 (space group I 4/ mmm) tetragonal structure at room temperature. Rietveld profile refinement of the powder pattern gave detailed structural parameters. The Si atoms are found to preferentially occupy the 8⨍ site with some small occupancies also for both the 8 i and 8 j sites. A minority impurity phase has been identified as that of the cubic NaZn 13-type structure (space group Fm 3c) . This present neutron diffraction investigation of metalloid substitution on the three transition metal sublattices in this structure type, as well as previous neutron studies, confirm that both atomic size and enthalpy effects are important in determination of preferential site ordering.

Directing Effect Of Fluoride In The Synthesis Of Molecular Sieves With New Characteristics And Of The First Twenty-Membered Ring Microporous Solid

ABSTRACTThe directing effect of fluoride anions in the synthesis of molecular sieves seems to be related to the strength of its interaction with the framework. For example, whereas F is bridging 2 Al atoms of a four-membered ring in AlPO4-5 containing tetrapropylammonium fluoride and in an new triclinic morpholine-containing chabazite-like AlPO4, it is found in double four-rings in three other phases which were synthesized recently. Firstly in the tetragonal all-silica AST-type octadecasil (space group I4/m, a = 9.194(2)Å c = 13.396(4)Å) which was obtained in the presence of quinuclidine and HF. Secondly in two novel cubic microporous gallophosphates which are formed selectively in the presence of hydrofluoric acid. One has the structure type LTA (space group Fm3c, a = 24.0354(1)Å) and crystallizes with di-n-propylamine as a template, and the other shows a novel structure type (space group Fm3c, a = 51.84Å) with a 3-dimensional 20-membered ring channel system. This is the largest membered ring ever reported for a synthetic material.

Low pressure and temperature dependent phase transitions of a potassium exchanged zeolite A

Phase transitions of an A-type zeolite with the chemical composition K 10.6Na 0.7[(SiO 2) 12(AlO 2) 11.9]-23.3 H 2O were investigated at atmospheric pressure and during evacuation (10 −6 ⩽ p ⩽ 1 bar) and at temperatures from 20 to 650 K using X-ray diffraction. At room temperature and down to a pressure of 1 mbar the structure is cubic ( a = 24.5 A ̊ ) with the space group Fm 3c . From 1 to 0.1 mbar a new cubic phase having the primitive space group Pm 3n appears without a change of the lattice constant. At lower pressures the space group is again Fm 3c . Dehydration by heating in vacuum exhibits a rhombohedral phase with space group R 3m . All transitions show hysteresis.

The structure of a carbon monoxide adduct of zeolite 5A

The structure of Ca 5Na 2-A:5CO has been determined at room temperature using Rietveld profile refinement in space groupFm3c witha refined to 24.6558(2)A˚. The finalR pw was 3.5%. As in the case of dehydrated zeolite 5A, the exchangeable cations are located in S1 (6-ring) sites, with Ca-O and Na-O distances of 2.32 and 2.37A˚. The carbon atoms of the carbon monoxide molecules have been located on the three-fold axis in the α-cage in a position analogous to that found in the CO complex of cobalt-exchanged zeolite A. However, the oxygen atoms are either undergoing considerable thermal motion or are disordered over several off-axis locations. The Ca-C distance is 2.83A˚. Inside the β-cage, with site occupancy approximately three-fourths, there are AlO 4H 3 tetrahedral species evenly distributed between two orientations, as has been found previously in studies of divalent exchanged samples of zeolite A. This aluminum complex bonds to the framework via Al-O-H … O(3) hydrogen bonds and there is coordination of the non-hydrogen-bearing oxygen atom to exchangeable calcium ions (Al-O … Ca).

ChemInform Abstract: Synthesis and Structure Investigations of Iodocuprates(I). Part 7. [Cu36I56 ]20‐ ‐ A Novel Polyanion in the Compound (pyH)2(Cu3I5).

AbstractThe title Compound has been isolated from the pyridiniumiodide/CuI system and it crystallizes in the cubic space group Fm3c with Z = 96·[(pyH2)2(Cu3I5)].

The structure of dehydrated zeolite 5A ( [formula omitted]) by neutron profile refinement

The structure of a commercially available, dehydrated sample of Linde Molecular Sieve 5A was refined using neutron powder profile analysis. Refinements were attempted in the accepted space group Fm 3c , in pseudo-cell Pm 3m , and also, using a lower-symmetry model, in space group F432. In Fm 3c , ( a = 24.6497(8) Å) the final R pw obtained was 13.6% while in Pm 3m ( a = 12.3254(4) Å) the final R pw was 14.25%. The reasons for the relatively high values of R pw compared with previous studies are discussed in terms of cation disorder and distortion of the framework. All the Ca 2+ ions are located in a 6-ring site just inside the β cage while all the Na + ions are located in a 6-ring site just inside the α cage. No cations were found in the 8-ring site.

The structure of dehydrated zeolite 3A (Si/Al = 1.01) by neutron profile refinement

A neutron powder diffraction study of a dehydrated commercially available potassium exchanged zeolite A (Linde 3A) has shown that the diffraction pattern can be indexed in cubic space group Fm 3c . For this sample there is 63% exchange of potassium for sodium (K +/Na + = 1.69). Data collected at a neutron wavelength of 2.98 Å shows no evidence of rhombohedral distortion and suggests that the assignment of space group Fm 3c is correct. The final structural model is closely analogous to that found for dehydrated sodium zeolite A ( J. M. Adams, D. A. Haselden, and A. W. Hewat, J. Solid State Chem. 44, 245 (1982) ; J. J. Pluth and J. V. Smith, J. Amer. Chem. Soc. 102, 4074 (1980) . Unusual features of previous refinements of potassium containing zeolite A samples, i.e., “zero coordinate” cations (P. C. W. Leung, M. B. Kunz, K. Seff, and I. E. Maxwell, J. Phys. Chem. 83, 741 (1979)) or potassium inside the β-cage ( J. J. Pluth and J. V. Smith, J. Phys. Chem. 83, 741 (1979) ) have not been found. Refinements using the same 1.9 Å neutron powder diffraction data were also obtained with the models of Leung et al. and Pluth and Smith (1979) as starting points (denoted LKSM and PS, respectively) and comparison is made with these. The final R factors for the three refinements were R pw ( A. K. Cheetham and J. C. Taylor, J. Solid State Chem. 21, 253 (1977) ) = 10.24% for the model presented here, R pw = 10.38% (PS model), and R pw = 10.61% (LKSM model).

A study of Si,Al ordering in thallium zeolite-A by powder neutron diffraction

The cubic structure of thallium zeolite-A has been studied by high resolution powder neutron diffraction. Refinements in which Si and Al are strictly alternating within the aluminosilicate framework (space group Fm3c) are better than those in which each Si is linked, by oxygen bridges, to three Al and one Si (space group Pn3n). This result is in accord with recent 29Si (magic-angle spinning) NMR measurements on zeolite ZK-4 but at variance with previous interpretations of NMR measurements on the sodium form of zeolite-A. Our conclusions reaffirm earlier X-ray results.

On the space group of zeolite-A

In the cubic (space group Fm3c) form of dehydrated Na-A zeolite, the Si,Al ordering, determined by neutron diffraction (Rietveld profile analysis) and 29Si (magic-angle spinning) n.m.r. spectroscopy, is shown to be 4 : 0 (i.e. each Si is tetrahedrally co-ordinated, via oxygen bridges, to four Al); this reaffirms earlier X-ray results.