Cancrinite Cages Research Articles

The crystal structure of ZSM-10, a powder X-ray and electron diffraction study

Abstract The crystal structure of the aluminosilicate, ZSM-10 (T108O216, where T = Si, Al), has been determined from electron diffraction and powder X-ray diffraction data. The material crystallizes in space group P6/mmm, where a = 31.390(2), c = 7.5147(8) Å. The framework [001] projection was determined independently with 300 kV precession electron diffraction amplitudes by direct methods. T-site positions in this projection were consistent with two models proposed in 1996 by Higgins and Schmitt. Subsequent Rietveld refinement favors their model A, comprising stacked cancrinite cages and hexagonal prisms. The framework density is 16.6 T sites/1000 Å3, similar to zeolite framework LTL. However, the refinement against synchrotron data from a dehydrated sample (R wp = 0.1600, R(F 2) = 0.1418) finds no extra-framework species, despite the detection of some K+ in the material.

Ultramarine analogs synthesized from cancrinite

The colored products analogous to ultramarine have been obtained by thermal treatment (500–800 °C) of cancrinite mixed with elemental sulfur and alkalis. The samples obtained at 500 °C maintain the original structure of cancrinite, while heating of the mixture at 800 °C resulted in zeolite structure transformation towards SOD in the case of mixture containing Na + cations and to kaliophilite or unknown structures, when K + or Li + were applied as alkali sources. Encapsulation of sulfur species inside the cancrinite cages does not result in the generation of another radicals but S 3 - or S 2 - , which is reflected in the ESR spectra resembling those embedded in sodalite cages.

Farneseite, a new mineral of the cancrinite - sodalite group with a 14-layer stacking sequence: occurrence and crystal structure

ab S tra C t This paper reports the occurrence and the crystal structure of fantappieite, a new member of the cancrinite-sodalite group of minerals from Torre Stracciacappe, Trevignano community (Rome, Latium, Italy). The mineral occurs within a volcanic ejectum consisting of dominant sanidine with minor plagioclase, biotite, augitic clinopyroxene, andradite, and iron oxides. Fantappieite (0.7 mm as largest size) is observed within miarolitic cavities of the rock as transparent colorless crystals, showing complex morphologies and striated faces. It is non-pleochroic and uniaxial negative, nω = 1.5046(5) and ne = 1.5027(5). Dcalc is 2.471 g/cm 3 . Fantappieite is trigonal, space group P3; the cell parameters are: a = 12.8742(6), c = 87.215(3) A, V = 12518.8(9) A 3 , Z = 1. The empirical chemical formula is: (Na84.12Ca30.00K15.95Fe0.19Ti0.13Mn0.10Mg0.09)(Si99.36Al98.64)O396(SO4)30.24(CO3)0.29Cl0.84F0.82∙5.18H2O, which corresponds to the ideal formula [Na82.5Ca33K16.5]Σ=132(Si99Al99O396)(SO4)33·6H2O. The five strongest reflections in the X-ray powder pattern are [d in A (I %) (hkl)]: 3.70 (100) (3 0 0), 3.60 (80) (1 0 23), 2.641 (65) (0 0 33), 6.85 (60) (0 1 10), 6.40 (55) (1 1 0). The single-crystal FTIR spectrum rules out OH groups and shows the presence of H 2O and CO2 molecules, as well. The structure can be described as a stacking sequence of 33 layers of six-membered rings of tetrahedra along the c axis. The stacking sequence is ACBACABACBACBACBCACBACBACBABCBACB…, where A, B, and C represent the positions of the rings within the layers. This sequence gives rise to liottite, sodalite, and cancrinite cages, alternating along c. Sulfate groups occur within the liottite cages associated by Na, K, and Ca, while highly disordered sulfate groups are located within the sodalite cages. H 2O groups occur within the cancrinite cages, bonded to Ca and Na cations. Split positions are found for Na-Ca sites, and are related to disordering of the sulfate groups in the sodalite cages.

Crystal structure of a new representative of the cancrinite group with a 12-layer stacking sequence of tetrahedral rings

The crystal structure of a 12-layer tounkite-like mineral of the cancrinite group was determined for the first time by single-crystal X-ray diffraction analysis (the unit-cell parameters are a = 12.757 A, c = 32.211 A). The structure was refined in the space group P3 to R = 0.035 using 3834 reflections with | F| > 2σ(F). Si and Al atoms occupy tetrahedral framework positions in an ordered fashion. The average distances in the tetrahedra are 〈Si-O〉 = 1.611 A and 〈Al-O〉 = 1.723 A. The stacking sequence of the layers is described as CACACBCBCACB, where A, B, and C are six-membered rings arranged around the [2/3 1/3 z], [1/3 2/3 z], and [0 0 z] axes, respectively. In the structure of the mineral, the columns along the [0 0 z] axis are composed of cancrinite cages. The columns along the [2/3 1/3 z] and [1/3 2/3 z] axes contain alternating cancrinite, bystrite, and liottite cages.

The crystal structure of giuseppettite, the 16-layer member of the cancrinite–sodalite group

Giuseppettite, chemical formula Na 42K 16Ca 6Si 48Al 48O 192(SO 4) 10Cl 2 · 5H 2O, space group P31 c, a=12.856, c=42.256 Å, is the 16-layer member of the cancrinite–sodalite group. It is characterised by an ABABABACBABABABC… stacking sequence of layers. The crystal structure of giuseppettite was solved and refined against data collected at the Elettra synchrotron facility, using a 0.3 × 0.2 × 0.2 mm 3 single crystal, twinned on (0 0 1), λ=0.9989 Å, R=0.074 for 3769 reflections, R=0.073 for 3706 reflections with F o>4 σ( F o). The structure contains two big cages (“giuseppettite” cages) along [0,0, z], and sequences CCSCCCS of “cancrinite” ( C) and “sodalite” cages ( S) both along [1/3,2/3, z] and [2/3,1/3, z]. Four sulphate groups surrounded by sodium cations, and alternated with potassium cations, are located within the giuseppettite cages, whereas a partially ordered distribution of sulphate groups and chlorine anions occurs within the sodalite cages. The cancrinite cages host sodium cations and water molecules.

The crystal structure of a "disordered" cancrinite

An X-ray single-crystal structural investigation on a sample of cancrinite of formula Na 7.13 Ca 0.87 (Si 6 Al 6 O 24 ) (SO 4 ) 0.07 (CO 3 ) 1.43 2H 2 O has been carried out. The cancrinite cage content has been found to be similar to that reported in previous structure refinements on natural and synthetic samples. However, differently from reference data, cations located inside the uninterrupted channel are distributed between two independent sites M1 and M2. Moreover carbonate groups are distributed, with partial occupancy, between two different z elevations (Cl-OC1 and C2-OC2). The tetrahedral co-ordination of the sulphate group is obtained by partial substitution of carbon atoms at C1 and C2 by sulphur and oxygen. Two possible orientation with the apical oxygen pointing “down” or “up” are possible.

Marinellite, a new feldspathoid of the cancrinite-sodalite group

Marinellite, [(Na,K) 42 Ca 6 ](Si 36 Al 36 O144)(SO 4 ) 8 Cl 2 .6H 2 O, cell parameters a = 12.880(2) A, c = 31.761(6) A, is a new feldspathoid belonging to the cancrinite-sodalite group. The crystal structure of a twinned crystal was preliminary refined in space group P 31 c , but space group P 62 c could also be possible. It was found near Sacrofano, Latium, Italy, associated with giuseppettite, sanidine, nepheline, hauyne, biotite, and kalsilite. It is anhedral, transparent, colourless with vitreous lustre, white streak and Mohs9 hardness of 5.5. The mineral does not fluoresce, is brittle, has conchoidal fracture, and presents poor cleavage on {001}. D meas is 2.405(5) g/cm 3 , D calc is 2.40 g/cm 3 . Optically, marinellite is uniaxial positive, non-pleochroic, ω = 1.495(1), ϵ = 1.497(1). The strongest five reflections in the X-ray powder diffraction pattern are [d in A (I) ( hkl )]: 3.725 (100) (214), 3.513 (80) (215), 4.20 (42) (210), 3.089 (40) (217), 2.150 (40) (330). The electron microprobe analysis gives K 2 O 7.94, Na 2 O 14.95, CaO 5.14, Al 2 O 3 27.80, SiO 2 32.73, SO 3 9.84, Cl 0.87, (H 2 O 0.93), sum 100.20 wt %, less O = Cl 0.20, (total 100.00 wt %); H 2 O calculated by difference. The corresponding empirical formula, based on 72 (Si + Al), is (Na 31.86 K 11.13 Ca 6.06 )Σ=49.05(Si 35.98 Al 36.02 )Σ=72O 144.60 (SO 4 ) 8.12 C1 1.62 3.41H 2 O. The crystal structure of marinellite may be described as formed by the stacking along c of 12 layers containing six-membered rings of tetrahedra: the stacking sequence is ABCBCBACBCBC…, where A, B, and C represent the positions of the rings within the layers. Its structure consists of two liottite cages superimposed along [0, 0, z ] and of columns of cancrinite and sodalite cages along [1/3, 2/3, z ] and [2/3, 1/3, z ]. Sulphate groups, surrounded by sodium, calcium and potassium cations, occupy the liottite cages. Chlorine anions and sulphate groups occupy the sodalite cages, whereas H 2 O molecules are located within the cancrinite cages, bonded to Na cations. This structural model was refined in the space group P 31 c , conventional R = 0.098 for 2155 reflections. The structural relationships between marinellite and tounkite are discussed.

Synthesis and crystal structures of gallium and germanium variants of cancrinite

A synthetic aluminogermanate and a gallogermanate with the Cancrinite group (CAN) framework topology have been synthesized under hydrothermal conditions and characterized by single crystal synchrotron X-ray diffraction. AlGe-CAN, Na 6Cs 2Al 6Ge 6O 24 · Ge(OH) 6, is hexagonal, with the space group P6 3 and a=12.968(1), c=5.132(1) Å, V=747.4(1) Å 3. The T-sites exhibit complete ordering of Al and Ge atoms, similar to the framework models of aluminosilicate analogues. GaGe-CAN, Na 6Cs 2Ga 6Ge 6O 24 · Ge(OH) 6, is hexagonal, apparently with the space group P6 3mc and a=12.950(2), c=5.117(1) Å, V=743.2(2) Å 3. Although the observed data are consistent with the presence of the c-glide and consequent disordering of Ga and Ge atoms at the T-sites, calculation using a DLS-optimized framework in the space group P6 3 reveals that the intensities of the hh 2h l reflections with l=2 n+1 are less than 0.07% of the strongest (0 0 0 2) reflection, suggesting that P6 3 is probably the true space group. Resonant diffraction studies performed in the vicinity of the Ga K-edge confirmed the presence of the hh 2h l reflections with l=2 n+1 and thus confirmed the ordering of the framework Ga/Ge atoms in GaGe-CAN. Inspection of the framework T–O–T bond angles demonstrates greater relative cell contraction for GaGe-CAN compared to AlGe-CAN and aluminosilicate counterparts. In both the structural models, Ge(OH) 6 octahedra are occluded in the 12-ring channels running along the 6 3-axes. The sodium cations fully occupy the sites above the 6-ring windows in the 12-ring channels. The cesium cations fully occupy the sites in the middle of the cancrinite cages. Subtle differences in the coordination geometries of the extra-framework species are found, perhaps due to the pseudo-symmetry of GaGe-CAN. Thermogravimetry results indicate net weight losses of 3.5% and 3.0% for AlGe-CAN and GaGe-CAN, respectively, which are explainable by the dehydration of the Ge(OH) 6 octahedra. In situ synchrotron X-ray powder diffraction demonstrated the formation of GaGe analogue of the nepheline hydrate I type structure at the temperature of complete dehydration.

The role of barium cations in the synthesis of low-silica LTL zeolites

The structure and extraframework atoms of the dehydrated zeolites (Ba,K)-GL (Ba 10K 16Si 36Al 36O 144) and (Ba,Li)-GL (Ba 18Si 36Al 36O 144) are characterized by powder neutron diffraction. The frameworks have the LTL topology and are refined in the hexagonal space group P 6/m c c (no. 192). Barium cations fully occupy the centers of the cancrinite cages (site B) and the positions between adjacent cancrinite cages (site C). In (Ba,K)-GL, potassium cations fully occupy sites above the centers of the eight-rings (site D), which line the pores of zeolite (Ba,K)-GL, whereas in (Ba,Li)-GL, barium cations occupy two-thirds of the site D positions. The syntheses and structural refinements of LTL zeolites show that barium and potassium play analogous structure-directing roles in LTL zeolites with different Si/Al ratios. The nearly identical sizes of barium and potassium allow these cations to have optimal coordination with framework oxygens in sites B, C, and D. Barium (a divalent cation) is used in the synthesis of low-silica LTL zeolites, and its role is equivalent to potassium (a monovalent cation) in the synthesis of higher-silica (Si/Al=3) LTL zeolites where potassium also occupies sites B, C, and D. In the absence of a sufficient amount of barium in the synthesis gel, other phases are formed immediately after all the barium cations have been consumed by the zeolite GL crystals.

Characterization of cancrinite synthesized in 1,3-butanediol by Rietveld analysis of powder neutron diffraction data and solid-state 23Na NMR spectroscopy

The framework structure and extraframework atoms of calcined and dehydrated cancrinite synthesized in 1,3-butanediol are characterized by powder neutron diffraction and 23Na nuclear magnetic resonance (NMR) spectroscopy. The cancrinite structure is refined in the hexagonal space group P6 3 (No. 173) with lattice parameters a=12.659 Å and c=5.153 Å. Carbonate anions are found occluded in the pores of the cancrinite structure. Although there are two different crystallographic cation sites found by the Rietveld refinement, there are three peaks in the 23Na magic-angle spinning (MAS) NMR spectrum. These peaks correspond to sodium cations found in site I inside the cancrinite cages, cations in site II inside the cancrinite pore without neighboring carbonates, and cations in site II with neighboring carbonates. Quadrupole coupling constants (QCC) obtained by a simple point-charge model agree well with the simulation of the 23Na MAS NMR spectra.

Crystal chemistry of the zeolites erionite and offretite

This study clarifies the crystal structure variations and relationships in the zeolites erionite and offretite. The crystal structure analyses used Rietveld analysis of X-ray powder diffraction data, obtained both by synchrotron radiation and conventional X-ray sources, and on diffraction patterns obtained by transmission electron microscopy. The framework Al atoms in erionite are preferentially located in the single six-membered ring of tetrahedra (T2 site), whereas the Si-Al distribution is essentially disordered on the tetrahedral framework sites in offretite. In both zeolites, the center of the cancrinite cage is always occupied by K cations in similar amounts in both minerals. The erionite cage in erionite is occupied by Ca and Na atoms distributed on four distinct cation sites. Mg ions can be present up to 0.8 atoms per cell and are located between the Ca1 and Ca3 sites and very close to the Ca2 site on the symmetry axis. In offretite, the Mg site is located on the trigonal axis of the gmelinite cage and the Mg atoms are bonded to a variable number (five or six) of H 2 O molecules, depending on the site population. The structural data and TEM analysis clearly show that the crystal chemistry of the extraframework cations, Mg in particular, is a major factor controlling whether erionite or offretite crystallizes, the Si-Al distribution in the framework, and the possible stacking intergrowths of the two minerals.

Surface Structure of Zeolite L Studied by High-Resolution Electron Microscopy

Termination structures of surfaces of zeolite L crystals are studied by high-resolution electron microscopy (HREM). By comparing observed HREM images with simulated ones based on some ideal models of the surface structure, a reliable surface structure model is proposed. The framework of the structural model is terminated with double six-membered rings on the (001) surface and with cancrinite cages on the (100) and (110) surfaces of the crystallite.

A reexamination of the crystal structure of erionite

The crystal structure of a natural erionite from Nizhnyaya Tunguska, Siberia (schematic formula K 2 Ca 3.5 Al 9 Si 27 O 72 · 32H 2 O) has been refined to a residual wR of 0.044. The erionite framework can be described by a sequence AABAAC … of 6-membered rings of tetrahedra. The (Si, Al) distribution (24% of Al in T1 and 31% of Al in T2) is consistent with the strong disorder found in tetrahedral sites for all zeolites describable by a sequence of 6-rings. Erionite, as in the closely related zeolite offretite, shows a slight enrichment of Al in the single 6-ring. K is at the center of the cancrinite cage and coordinates 6 framework oxygen atoms. Ca atoms alternately occupy three sites, quite near each other, on the triad axis parallel to c , at the center of the erionite cage. Their coordination number varies between 6 and 9. The marked differences in T—O distances found between hydrated and dehydrated erionite are explained in terms of interactions between extraframework ions and framework oxygens.

Cupric Ion Location and Adsorbate Interactions in Cu(II) Exchanged Erionite-like SAPO-17 Molecular Sieve

Erionite-like silicoaluminophosphate molecular sieve SAPO-17 has been synthesized using cyclohexylamine as the organic structure directing molecule. The location of Cu(II) ions exchanged into H-SAPO-17 and the interaction of Cu(II) ions with water, ammonia, methanol, and ethylene have been investigated by electron spin resonance (ESR) and electron spin echo modulation (ESEM) techniques. Simulation parameters of the 31P ESEM spectrum suggest that the hydrated Cu(II) complex, CuII(H2O)6, is located in the erionite supercage. During dehydration some of the bare Cu(II) ions migrate into the smaller cancrinite cage. Room temperature adsorption of D2O on CuH-SAPO-17 after dehydration at 723 K and subsequent O2 treatment and evacuation at the same temperature (activation) forms a Cu−aquo complex with axially symmetric ESR parameters (g|| = 2.391 and A|| = 0.0142 cm-1). This complex is suggested to be CuII(D2O)3 based on 2D ESEM data. Adsorption of ND3 on activated CuH-SAPO-17 produces CuII(ND3)3 with axially sym...

The effects of lattice composition on the physicochemical properties of H-offretite crystals

Several spectroscopic techniques have been used to investigate the acidic properties of a set of galliosilicate molecular sieves with the offretite structure. IR spectra in the OH stretching region contain well-defined bands at or near 3735, 3640, 3600 and 3550 cm −1 that can be attributed to OH groups associated with SiOH, and with M(IV)OH groups located in secondary building units, in the main channels (or in the gmelinite cages), and with M(IV)OH groups associated with oxygens shared by the main channels and the cancrinite cages; M = Al,Ga. Spectra of chemisorbed pyridine show that all crystals contain both Bronstedt (B) and Lewis (L) acid sites, and that the presence of Ga seems to decrease B-acid strength and to increase the L-sites' density and strength. Microcalorimetry experiments with ammonia and pyridine as probe molecules show that Ga insertion into the aluminosilicate framework increases the strength of the strongest acid sites and that the presence of Ga generate a heterogeneous distribution of acid site strengths absent in the parent Al-analogs. Moreover, in H,Ga-offretites, there is a drastic reduction in acid site density while the initial acid site strength remains high. NMR results suggest that the observed effects can be attributed, in part, to the presence of extra-framework Al and Ga atoms. Levels of Al(VI) and Ga(VI), as well as partial lattice degradation, strongly depend on the NH 4-exchange and calcination procedure used to activate these offretite crystals.

A reexamination of the crystal structure of the zeolite offretite

The crystal structure of a natural offretite from Poia Creek, Adamello, Italy (schematic formula KCaMgAl 5 Si 13 O 36 :17 H 2 O) has been refined to a residual wR of 0.038. The offretite framework can be described by a sequence AABAAB … of 6-membered rings of tetrahedra. The (Si,Al) distribution (29% of AI in T1 and 37% of AI in T2) is consistent with the disorder found in tetrahedral sites for ail zeolites describable by sequences of 6-rings. K is at the center of the cancrinite cage and is coordinated to 6 framework oxygen atoms. Mg, placed at the center of the gmelinite cage, is coordinated to 6 water molecules; 4 of these are disordered on 9 possible positions relative to two sites with multiplicity 6 and 3, respectively. Ca atoms alternately occupy two sites near each other, at the center of the wide channel parallel to parameter c, and are octahedrally coordinated to the same water molecules. The strong differences in the T−O distances found between hydrated and dehydrated offretite are here explained in terms of interactions between extraframe-work ions and framework oxygens.

ZSM-10: Synthesis and tetrahedral framework structure

A reproducible, scaleable synthesis of ZSM-10 is reported. This synthesis is dependent on the presence of 1,4-dimethyl-DABCO cations during the nucleation/aging stage, but this directing agent is not incorporated in the final product. Analysis of the zeolite product during aging shows that offretite is formed first and then converts to ZSM-10. The framework topology of ZSM-10 (K24Al24Si84O216 · xH2O · yR) has been determined from synchrotron X-ray and electron diffraction data, model building, and X-ray powder pattern simulation. ZSM-10 has a large hexagonal unit cell with a = 31.575(7) A, c = 7.525(4) A, P6/mmm maximum topological symmetry, and a tetrahedral framework density of 16.6 T/1,000 A3. The tetrahedral framework is constructed from columns of alternating cancrinite cages and double 6-rings which also build the LTL (Linde Type L or zeolite L) and OFF (offretite) frameworks. Two different one-dimensional, 12-ring pore systems parallel the caxis in ZSM-10. One 12-ring channel is topologically identical to the undulating channel in the LTL framework, and the other is identical to the 12-ring channel in the OFF framework. ZSM-10 appears to be the first zeolite with two distinct, parallel, 12-ring channel systems that occur individually in other zeolites.

Structure and Stability of Zeolite Offretite under Si4+/(Al3+, M+) Substitution (M = Na, K): A First Principles Molecular Dynamics Study

A local density functional study of the structure and energetics of offretite, with a Si4+ ion substituted by (A13+, M+) (M = Na, K), is presented. The calculations have been performed within the framework of the first principles molecular dynamics method using a periodically repeated unit cell with 55 atoms. It is found that the preferred site for K+ cations lies inside the cancrinite cage, in agreement with experiment. This site is related to A1 substituting a Si atom at a TI site, which is one of the two inequivalent tetrahedral sites of offretite, and belongs to the hexagonal prism, Site selectivity is quite pronounced in the case of K+, as the large size of this cation gives rise to important steric effects in the offretite framework. For Na+, instead, the lowest energy site is located in the channel, near a window of the cancrinite cage, and corresponds to an A1 in Tz. For this cation the spread in the relative substitution energies of the different binding sites is very small, the four sites of lower energies being in a range of -2.5 kcal/mol.

Identification of Pd3+ ions in zeolite L by temperature programmed reduction and electron paramagnetic resonance spectroscopy

Pd supported on KL zeolite has been studied by temperature programmed reduction (TPR) and electron paramagnetic resonance (EPR) spectroscopy. It has been found that upon calcination in pure oxygen Pd3+ and Pd2+ ions are formed; the Pd3+ ions are identified by their EPR signal. As Pd3+ ions in the cancrinite cages are difficult to reduce, the H2 consumption in conventional TPR is below the stoichiometric amount.

Synthesis and structure of lithium cesium and lithium thallium cancrinites

X-ray powder diffraction studies of synthetic cancrinites were undertaken to elucidate the role of lithium ions and large cations (Cs, Tl) in zeolite crystallizations. Li4.56Cs1.50Al6Si6O24, 4.9 H2O (a = b = 12.4328 (12) Å, c = 4.9692 (6) Å, hexagonal, P63, Z = 1). The structure was refined by the Rietveld diffraction-profile refinement technique. The cesium ions — located in the cancrinite cage only — are coordinated to 12 oxygen atoms (at distances 3.15–3.61 Å). In accordance with their position, they are not exchangeable. The lithium ions are four coordinated to oxygen atoms (at distances 1.91 to 2.03 Å). Li2.75Tl3.23Al5.85Si6.13O24, 2.0 H2O (a = b = 12.4419 (7) Å, c = 4.9884 (4) Å, hexagonal, P63, Z = 1. The thallium ions are located on more than one position in the cancrinite cage, and there is also thallium on one position in the channels. This is in accordance with the thallium ions being partially exchangeable in this material. The structures are described and the action of small and large ion radius cations in cancrinite crystallization is discussed.