Crystal Chemistry of Stanfieldite, Ca7M2Mg9(PO4)12 (M = Ca, Mg, Fe2+), a Structural Base of Ca3Mg3(PO4)4 Phosphors

Stanfieldite, natural Ca-Mg-phosphate, is a typical constituent of phosphate-phosphide assemblages in pallasite and mesosiderite meteorites. The synthetic analogue of stanfieldite is used as a crystal matrix of luminophores and frequently encountered in phosphate bioceramics. However, the crystal structure of natural stanfieldite has never been reported in detail, and the data available so far relate to its synthetic counterpart. We herein provide the results of a study of stanfieldite from the Brahin meteorite (main group pallasite). The empirical formula of the mineral is Ca8.04Mg9.25Fe0.72Mn0.07P11.97O48. Its crystal structure has been solved and refined to R1 = 0.034. Stanfieldite from Brahin is monoclinic, C2/c, a 22.7973(4), b 9.9833(2), c 17.0522(3) Å, β 99.954(2)°, V 3822.5(1)Å3. The general formula of the mineral can be expressed as Ca7M2Mg7(PO4)12 (Z = 4), where the M = Ca, Mg, Fe2+. Stanfieldite from Brahin and a majority of other meteorites correspond to a composition with an intermediate Ca≈Mg occupancy of the M5A site, leading to the overall formula ~Ca7(CaMg)Mg9(PO4)12 ≡ Ca4Mg5(PO4)6. The mineral from the Lunar sample “rusty rock” 66095 approaches the M = Mg end member, Ca7Mg2Mg9(PO4)12. In lieu of any supporting analytical data, there is no evidence that the phosphor base with the formula Ca3Mg3(PO4)4 does exist

Crystal structure of (1R,5S)-endo-(8-methyl-8-azoniabicyclo[3.2.1]oct-3-yl)ammonium aquatrichloridonitratocopper(II)

The structure of a salt of diprotonated endo-3-aminotropane crystallized with a copper(II) anionic cluster is reported, viz. (C8H18N2)[CuCl3(NO3)(H2O)]. Neither ion in the salt has been structurally characterized previously. In the crystal, the ions pack together to form a three-dimensional structure held together by a network of intermolecular N—H...O, O—H...Cl and N—H...Cl hydrogen-bonding interactions. Selective crystallization of the title compound can be considered as a simple method for the separation of the exo and endo isomers of 3-aminotropane

The 7-azanorbornane nucleus of epibatidine: 7-azabicyclo[2.2.1]heptan-7-ium chloride

7-Azabicyclo[2.2.1]heptane (7-azanorbornane) 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 acetylcholine nicotinic receptor agonists, a plethora of literature has been devoted to this alkaloid. However, there are no structural data on the unsubstituted 7-azanorbornane, the parent bicyclic ring of epibatidine and its derivatives. We herein present the structural characterization of the 7-azabicyclo[2.2.1]heptane parent ring as its hydrochloride salt, namely 7-azabicyclo[2.2.1]heptan-7-ium chloride, C6H12N+·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

Water-Soluble Phosphine Capable of Dissolving Elemental Gold: The Missing Link between 1,3,5-Triaza-7-phosphaadamantane (PTA) and Verkade’s Ephemeral Ligand

We herein describe a tricyclic phosphine with previously unreported tris­(homoadamantane) cage architecture. That water-soluble, air- and thermally stable ligand, 1,4,7-triaza-9-phosphatricyclo­[5.3.2.1^4,9]­tridecane (hereinafter referred to as CAP) exhibits unusual chemical behavior toward gold and gold compounds: it readily reduces Au­(III) to Au(0), promotes oxidative dissolution of nanocrystalline gold(0) with the formation of water-soluble trigonal CAP–Au­(I) complexes, and displaces cyanide from [Au­(CN)₂]⁻ affording triangular [Au­(CAP)₃]⁺ cation. From the stereochemical point of view, CAP can be regarded as an intermediate between 1,3,5-triaza-7-phosphaadamantane (PTA) and very unstable aminophosphine synthesized by Verkade’s group: hexahydro-2<i>a</i>,4<i>a</i>,6<i>a</i>-triaza-6<i>b</i>-phosphacyclopenta­[<i>cd</i>]­pentalene. The chemical properties of CAP are likely related to its anomalous stereoelectronic profile: combination of strong electron-donating power (Tolman’s electronic parameter 2056.8 cm^–1) with the low steric demand (cone angle of 109°). CAP can be considered as macrocyclic counterpart of PTA with the electron-donating power approaching that of strongest known phosphine electron donors such as P­(<i>t</i>-Bu)₃ and PCy₃. Therefore, CAP as sterically undemanding and electron-rich ligand populates the empty field on the stereoelectronic map of phosphine ligands: the niche between the classic tertiary phosphines and the sterically undemanding aminophosphines

Rudashevskyite, the Fe-dominant analogue of sphalerite, a new mineral: Description and crystal structure

ABStrAct Rudashevskyite, Fe-dominant analogue of sphalerite, is an accessory phase in the Indarch meteorite (enstatite chondrite, EH4). It occurs as xenomorphic polycrystalline grains, 5-120 µm in size, associated with clinoenstatite, kamacite, troilite, oldhamite, niningerite, schreibersite, and roedderite. Macroscopically, rudashevskyite is black with resinous luster. In reflected light, it is gray with brownish tint. Isotropic, no internal reflections