Karl Seff

Crystal structure of zeolite X nickel(II) exchanged at pH 4.3 and partially dehydrated, Ni2(NiOH)35(Ni4AlO4)2(H3O)46Si101Al91O384

Abstract Complete Ni2+ exchange of a single crystal of zeolite X of composition Na92Si100Al92O384 per unit cell was attempted at 73°C with flowing aqueous 0.05 M NiCl2 (pH=4.3 at 23°C). After partial dehydration at 23°C and ≈10−3 Torr for two days, its structure, now of composition Ni2(NiOH)35(Ni4AlO4)2(H3O)46Si101Al91O384 per unit cell, was determined by X-ray diffraction techniques at 23°C (space group Fd 3 , a0=24.788(5) A). It was refined using all intensities; R1=0.080 for the 236 reflections for which Fo>4σ(Fo), and wR2=0.187 using all 1138 unique reflections measured. At four crystallographic sites, 45 Ni2+ ions were found per unit cell. Thirty of these are at two different site III′ positions. Twenty of those are close to the sides of 12-rings near O–Si–O sequences, where each coordinates octahedrally to two framework oxygens, to three water molecules which hydrogen bond to the zeolite framework, and to an OH− ion. The remaining 10 are near O–Al–O sequences; only three members of a likely octahedral coordination sphere could be found. In addition, two Ni2+ ions are at site I, eight are at site I′, and five are at site II. Forty six H3O+ ions per unit cell, 24 at site II′ and 22 at site II, each hydrogen bond triply to six rings of the zeolite framework. Each of the 22 H3O+ ions also hydrogen bonds to a H2O molecule that coordinates to a site III′ Ni2+ ion. Six of the eight sodalite cages each contain four H3O+ ions at site II′; the remaining two each contains a tetrahedral orthoaluminate anion at its center. Each tetrahedral face of each orthoaluminate ion is centered by a site I′ Ni2+ ion to give two Ni4AlO4 clusters. The five site II Ni2+ ions each coordinate to a OH− ion. With 46 H3O+ ions per unit cell, the great tendency of hydrated Ni2+ to hydrolyze within zeolite X is demonstrated. With a relatively weak single-crystal diffraction pattern, with dealumination of the zeolite framework, and with an apparent decrease in long-range Si/Al ordering likely due to the formation of antidomains, this crystal like others treated with hydrolyzing cations appears to have been damaged by Ni2+ exchange and partial dehydration.

MOLECULES OF COPPER(II) l-SPARTEINE DINITRATE ARE MIXED FOUR- AND FIVE-COORDINATE IN ONE CRYSTALLINE PHASE AND ONLY FOUR-COORDINATE IN ANOTHER

Abstract A neutral complex of Cu(II) with the chiral bidentate nitrogen-chelating alkaloid (−)-sparteine, with nitrate groups occupying the remaining coordination sites, has been prepared and characterized. Solution conductivity measurements indicate that both nitrate groups are coordinated to copper to give a neutral molecule. Optical and electron-spin-resonance spectra in toluene/CHCl3, did not show a clear picture of the coordination geometry. A frozen-glass ESR spectrum showed the same evidence for mixed species, with the predominant species characterized by a very low A11 value of 118 G. Crystals 1 and 2 of Cu(C15H26N2)(NO3)2 were grown by two methods: 1 at 25°C from saturated acetonitrile, and 2 at 5°C from ethanol/dichloromethane under CCl4 vapor. Their structures were determined by X-ray crystallography. Crystals 1 were monoclinic, space group P21, with a = 7.851(6), b = 14.408(10), c = 16.079(10) A, β = 97.93(6)°, V = 1801(2) A and Z = 4. Crystals 2 were orthorhombic, space group P212121, with a ...

Extensive intrazeolitic hydrolysis of Zn(II): partial structures of partially and fully hydrated Zn(II)-exchanged zeolite X

Abstract Complete Zn 2+ exchange of two single crystals of zeolite X (Na 92 Si 100 Al 92 O 384 ) was attempted at 80°C from aqueous Zn(NO 3 ) 2 (pH=5.5 at 23°C). The structures of crystal 1 (partially dehydrated by evacuation at 23°C and 10 −3 Torr for two days) and crystal 2 (fully hydrated) were determined by X-ray diffraction techniques in the cubic space group Fd 3 at 23°C ( a o =24.750(5) and 24.872(6) A, respectively). They were refined using all intensities to the final error indices R 1 =0.126 and 0.116 based on the 428 and 348 reflections, respectively, for which F o >4 σ ( F o ). Each crystal has about 54 Zn 2+ ions per unit cell, indicating the uptake of eight excess Zn(OH) 2 molecules. In both crystals, further extensive hydrolysis of Zn 2+ is seen. Many non-framework oxygens were not found. In crystal 1, 34 Zn 2+ ions per unit cell occupy conventional cationic sites: 10 are at site I ′ , 12 at site II, and 12 at site III ′ . Three Zn 2+ ions each coordinate to a framework oxygen at a non-conventional site in the supercages. Three Zn 2+ ions at the centers of sodalite cavities each coordinate tetrahedrally to four non-framework oxygens to give (likely) Zn(OH) 2 (H 2 O) 2 which hydrogen bonds multiply to the zeolite framework. At three supercage positions, about 14 Zn 2+ ions that do not coordinate to the zeolite framework are found. Per unit cell, 37 H 3 O + ions are found: 20 at site I ′ and 17 at site II. It is presumed, considering the number of H 3 O + ions, that the latter 14 Zn 2+ ions are hydrolyzed Zn 2+ ions, likely hydrated Zn(OH) 2 molecules, some likely bridging. In crystal 2, 33 Zn 2+ ions per unit cell are found at conventional cationic sites: two at site I, 14 at two different sites I ′ , seven at site II, and 10 at site III ′ . As in crystal 1, three Zn 2+ ions each coordinate to a framework oxygen at a non-conventional site in the supercage. At three supercage positions, about 18 Zn 2+ ions that do not coordinate to the zeolite framework are found. Per unit cell, 40 H 3 O + ions are found: 18 at site II ′ and 22 at site II. Only about 16 non-framework oxygens were found per unit cell: eight water molecules in the supercages and, in the sodalite cages, eight hydroxide ions which participate in the formation of two nearly cubic Zn 4 (OH) 4 4+ clusters.

Weak Ag+–Ag+ bonding in zeolite X. Crystal structures of Ag92Si100Al92O384 hydrated and fully dehydrated in flowing oxygen

Abstract Two crystal structures of fully Ag + -exchanged zeolite X, one hydrated ( a =24.996(4) A) and the other fully dehydrated ( a =25.200(4) A), have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd 3 at 21(1)°C. Each initial Na 92 –X crystal was ion exchanged in a flowing stream of 0.05 M aqueous AgNO 3 . The second crystal was dehydrated at 360°C for two days in a flowing stream of oxygen gas (790 Torr) followed by evacuation at 400°C and 2×10 −6 Torr for 2 h. Their structures were refined to the final error indexes R 1 / R 2 =0.088/0.104 with 216 reflections, and R 1 / R 2 =0.047/0.041 with 312 reflections, respectively, for which I >3 σ ( I ). Both structures show weakly attractive 3.0–3.3 A Ag + –Ag + interactions. In the hydrated crystal , 92 Ag + ions were found at seven crystallographic sites: 16 fill site I at the centers of the double six-rings, 16 at site I ′ in the sodalite cavities opposite double six-rings bond weakly (3.045(3) A) to those at site I, 32 fill site II in the supercages, and 28 occupy four different III ′ sites. Some H 2 O molecules were found at two different 3-fold axis sites: 16 coordinate to site I ′ Ag + ions in the sodalite cavities, and 32 coordinate to site II Ag + ions in the supercage. In the dehydrated crystal , Ag ions or atoms were found at eight crystallographic sites: three Ag + ions are at site I, 26 Ag + ions and six Ag 0 atoms are at two I ′ sites in the sodalite cavities filling site I ′ , 32 Ag + ions fill site II as in crystal 1, two Ag 0 atoms are on 2-fold axes in the sodalite cavities, and 23 Ag + ions occupy three different III ′ sites. The 26 Ag + ions at site I ′ bond weakly in pairs (3.224(3) A). Three linear Ag 3 + clusters per unit cell with atoms at sites I ′ , I, and I ′ , respectively, lie along 3-fold axes, and two bent 168(2)° Ag 3 2+ clusters per unit cell are in the sodalite cavities. It remains possible, considering Ag–Ag and Ag–O distances, that no Ag 0 atoms have formed, that the product is (Ag + ) 92 –X, and that the bonding in the clusters, both of which would then be Ag 3 3+ , is due to additional Ag + –Ag + interactions.

Some chemical treatments diminish the long-range ordering in the aluminosilicate framework of zeolite X

Abstract The long-range ordering in the aluminosilicate framework of zeolite X is sometimes diminished or lost during aqueous ion exchange and/or subsequent dehydration. This observation is based on 46 single-crystal determinations of the structure of zeolite X modified by a wide range of chemical treatments. A relationship is seen between the loss of long-range ordering and acidity (H3O+ or H+) within the zeolite, whether the result of direct H3O+ exchange or the exchange of hydrolyzing cations into the zeolite. This effect is seen more strongly when ion exchange is done at an elevated temperature and when vacuum dehydration is attempted, especially at elevated temperatures. Further increases in acidity and/or temperature lead to the loss of the single-crystal diffraction pattern and ultimately to the physical break-up of the crystal, including dissolution if a solvent is present. All crystals, of initial composition Na92Si100Al92O384 per unit cell exclusive of water molecules, were taken from batches prepared by Petranovskii, and all appear to have had Fd 3 symmetry initially with a high degree of Si/Al ordering. After relatively little crystal damage, the space group appears to become Fd 3 m as would be expected if the long-range Si/Al ordering were lost. Before then, the distinction between the Si and Al positions, both initially relatively pure with Si and Al atoms, respectively, diminishes, and the mean apparent Si–O and Al–O bond lengths converge. It is proposed that these initial effects are caused by the loss of infinitesimal to small amounts of aluminum from the zeolite framework, allowing, by local recrystallization, antidomains with opposite Si/Al ordering to form.

Rate of Tl+ exchange into single crystals of zeolite X

Abstract A hydrated single crystal of zeolite X with unit-cell composition Na 92 Si 100 Al 92 O 384 , exclusive of water molecules, 0.14 mm in cross-section, was ion exchanged at 23°C with flowing 0.1 M aqueous TlNO 3 for 90 s. Its structure, determined crystallographically, showed that 74(4) of the 92 Na + ions per unit cell had been replaced by Tl + . A second crystal was treated similarly for 900 s; this time 83(1) Tl + ions were found. Kim et al. had found 91(1) Tl + ions after 7.0 days =6.0 × 10 5 s [Y. Kim, Y.W. Han, K. Seff, Zeolites 18 (1997) 325]. These results can be fit relatively well to a simple fourth-order rate law with k = 6.25 × 10 −7 (No. of Na + per unit cell) −3 s −1 . For crystals of such size, which are important for X-ray crystallography, days may not be enough time to reach an ion-exchange end point by these methods for some ions.

Lankalapuol a and b: two cis-eudesmanes from the sea hare

Abstract The marine mollusk Aplysia dactylomela is the source of two new brominated sesquiterpenes, lankalapuol A and B ( 1 , 2 ). Characterization is based on the spectral data of their acetates ( 3 , 4 ). The absolute stereochemistry of lankalapuol A acetate, (6 R ) acetoxy-(1 R )bromo-(5 R ,7 R .10 R )eudesm-3-ene, is based on X-ray analysis. The two lankalapuols are antipodal cis -fused eudesmanes.

The location of deuterium ions in zeolite Y by pulsed-neutron powder diffraction

Many structural studies have been conducted to determine the cation positions in faujasite type zeolites, including some to locate hydrogens which play a central role in acid catalysis. In this report, pulsed-neutron powder diffraction techniques were employed to determine the crystallographic positions of deuterium ions, and to learn the structure and placement of PbS species, in zeolite Y. 11 refs., 1 fig., 2 tabs.

Verification of linear Na32+ clusters in zeolite X

A fully dehydrated single crystal of zeolite Na–X at 250°C was exposed to 1.8 × 10−3 Torr of sodium vapor for three days. Its crystal structure shows that pairs of Na+ ions have each captured a Na0 atom to form a linear Na32+ cluster. These clusters span about 70% of the 12-oxygen rings. The remaining 12-rings each contain only one Na+ ion and have not participated in sodium atom sorption. The formation of elemental silicon on the crystal surface is proposed.

Complete redox exchange of indium for Tl+ in zeolite A. synthesis and crystal structure of fully indium-exchanged zeolite A

Indium has replaced all of the Tl + ions in fully dehydrated fully Tl + -exchanged zeolite A by a solvent-free redox ion-exchange reaction with In metal at 623 K. The crystal structures of the zeolite before (Tl 12 -A) and after the reaction, followed by washing with water and redehydration at 350 °C for 2 days (In 10 A·In), have been determined by single-crystal X-ray crystallography at 21°C. In 10 -A·In, elevent In atoms or ions per unit cell are distributed over seven crystallographically distinct positions. Seven In occupy three threefold-axis equipoints: four In + ions lie opposite 6-rings in large cavity, and two In 2+ and one In + lie opposite 6-rings in the sodalite unit. Three In + ions per unit cell are found at two different 8-ring, positions, 1.5 on the 8-ring plane and 1.5 off. Finally, one In 0 atom per unit cell is found at two quite unusual positions: half an In 0 at the center of sodalite unit and the other half In 0 opposite a 4-ring relatively deep in the large cavity. These In atoms associate with In, ions, likely forming (In 5 ) 8+ clusters in half of the sodalite units, and (In 3 ) 2+ clusters in half of the large cavities.