Search

Ion-exchange properties of natural caryochroite (Na,Sr) 3 {(Fe,Mg)2+ 10 (OH) 6 [TiO(Si 6 O 17)(OH) 0.5 ] 2 }·8H 2 O, a microporous heterophyllosilicate with a one-dimensional system of broad zeolytic channels, related to nafertisite Na 3 {Fe2+ 10 (OH) 6 [TiO(Si 6 O 17)F 0.5 ] 2 }·2H 2 O, were studied in reactions with 1 N aqueous solutions of Rb, Cs, Ag, and Pb nitrates at 50 °C. In reactions with Rb+, Cs+, and Pb2+, sodium is partly replaced by nearly equivalent amounts of larger cations. In reactions with Pb2+ and Ag+, additional processes involving H 2 O molecules take place: replacement of two H 2 O molecules with Pb2+ + 2OH− and replacement of H 2 O molecule with Ag+ + OH−, respectively. The geometrical-topological analysis of ion migration pathways in the nafertisite-type structures carried out using an approach based on the Voronoi-Dirichlet partition has shown that only Na+ cations occurring at the centers of wide channels can take part in reactions with large alkaline cations proceeding in counter flows. In the reaction with Ag+, additional Na+ ions are involved. Li+ cations having a smaller radius can pass through the window between the channels, forming a 2D conducting layer. Image 1 • Ion-exchange properties of natural titanosilicate caryochroite, a microporous heterophyllosilicate with a one-dimensional system of broad zeolytic channels, were studied in reactions with 1 N aqueous solutions of Rb, Cs, Ag, and Pb nitrates at 50 °C. • Three kinds of Na+ cations in the caryochroite structure play different role in ion migration processes. • Li+ cations having a smaller radius can pass through the window between the channels, forming a 2D conducting layer. [ABSTRACT FROM AUTHOR]

The chemistry of noble gases was for a long time dominated by fluoride-bearing compounds of xenon. However, the last two decades have brought new insights into the chemistry of xenon oxides and oxysalts, including insights involving a novel type of non-covalent interaction (aerogen bonding), discoveries of new xenon oxides, oxide perovskite frameworks and evidence for an abrupt increase of xenon reactivity under extreme pressure-temperature conditions. The complex implementation of these findings could facilitate the development of explanations for long-standing interdisciplinary problems, such as the depletion of heavy noble gases in contemporary planetary atmospheres - the cosmochemical enigma known as the "missing xenon" paradox.

Allabogdanite, (Fe,Ni) 2 P, is the only known natural high-pressure phase reported in the Fe-Ni-P system. The mineral, which was previously described from a single meteorite, the Onello iron, is now discovered in the Santa Catharina and Barbianello nickel-rich ataxites. The occurrence of allabogdanite in Santa Catharina, one of the largest and well-studied meteorites, suggests that this mineral is more common than was believed. The formation of allabogdanite-bearing phosphide assemblages in a given meteorite provides evidence that it experienced peak pressure of at least 8 GPa at a temperature above 800 °C. Since the pressure-temperature stability parameters of allabogdanite fall within the margins of the stishovite (rutile-type SiO 2 ) stability area, the former can be employed as a convenient stishovite-grade indicator of significant impact events experienced by iron and stony-iron meteorites and their parent bodies.

A hydroxyl-dominant analogue of gadolinite-(Y) (OH-Gad) has been discovered in the Heftetjern granitic pegmatite, southern Norway, in association with late-stage rare-earth-element containing minerals. The empirical formula, based on ten O atoms per formula unit, is (Y 1.285 Ca 0.55 Ce 0.07 La 0.04 Nd 0.01 ) Σ1.955 (Fe 2+ 0.57 □ 0.43 )Be 2.02 Si 1.995 O 8.48 (OH) 1.52 . The mineral is monoclinic, space group P2 1 /c, a = 4.7514 (10), b = 7.5719 (16), c = 9.9414 (2) Å, β = 90.015 (4)°, V = 357.663 (3) Å 3 and Z = 2. The density calculated using the empirical formula is 3.903 g cm -3 . The crystal structure was refined to R = 0.0217 for 776 reflections with I > 2σ(I). OH-Gad is isostructural with gadolinite-(Y) and it is characterized by the predominance of OH - over O 2- at the anionic Ø-site. The refined crystal-chemical formula is: A (Y 1.25 Ca 0.55 Ce 0.2 ) X (Fe 2+ 0.57 □ 0.43 ) Z Be 2 T Si 2 O 8 Ø [(OH) 0.86 O 0.59 (OH)* 0.55 ] (Z = 2). The possible orientation and local environment of the hydroxyl group were suggested based on bond-valence sum calculations and geometrical analysis of the crystal structure. The infrared spectrum confirms disordering of H atoms. OH-Gad seems to be a potentially new mineral, the first simultaneously hydroxyl- and iron-dominant member of the gadolinite subgroup. It is an OH-analogue of gadolinite-(Y) and an Fe 2+ -analogue of hingganite-(Y).

7-Aza-bicyclo-[2.2.1]heptane (7-aza-norbornane) is a bridged heterocyclic nucleus found in epibatidine, the alkaloid isolated from the skin of the tropical poison frog Epipedobates tricolor . Since epibatidine is known as one of the most potent acetyl-choline nicotinic receptor agonists, a plethora of literature has been devoted to this alkaloid. However, there are no structural data on the unsubstituted 7-aza-norbornane, the parent bicyclic ring of epibatidine and its derivatives. We herein present the structural characterization of the 7-aza-bicyclo-[2.2.1]heptane parent ring as its hydro-chloride salt, namely 7-aza-bicyclo-[2.2.1]heptan-7-ium chloride, C 6 H 12 N + ·Cl - . The compete cation is generated by a crystallographic mirror plane with the N atom lying on the mirror, as does the chloride anion. In the crystal, the cations are linked to the anions by N-H⋯Cl hydrogen bonds, which generate [001] chains.