New Data on the Isomorphism in Eudialyte-Group Minerals. ХI: Crystal Structure of a Potentially New Mineral—A Case of Complete Substitution of Fe2+ with $${\text{Na}}_{{{\text{2/3}}}}^{{\text{ + }}}{\text{Zr}}_{{{\text{1/3}}}}^{{{\text{4 + }}}}$$ in the Eudialyte-Type Structure

Crystallography Reports - The crystal structure and crystallochemical features of a Fe-deficient zirconium-rich analog of eudialyte from the Lovozero alkaline massif (Kola peninsula) have been...     

New Data on the Isomorphism in Eudialyte-Group Minerals. V: Crystal Structure of an Intermediate Member of the Manganoeudialyte‒Ilyukhinite Isomorphous Series

Crystallography Reports - The crystal structure of a high-symmetry representative of the eudialyte group from the Norra Kärr massif (Sweden) has been investigated by X-ray diffraction analysis...     

Crystal Structure of Cl-Deficient Analogue of Taseqite from Odikhincha Massif

An eudialyte group mineral, found in pegmatites of the Odikhincha massif (the northern part of the Siberian platform), has been investigated using X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The mineral is characterized by a high strontium content and a low chlorine content. It has a trigonal unit cell with the following parameters: a = 14.2700(6) Å and c = 30.057(1) Å; V = 5300.6(1) ų; sp. gr. R3m. The structure has been refined to R = 0.047 in the anisotropic approximation of atomic displacements using 1697F > 4σ(F). The idealized formula (Z = 3) was found to be Na₁₂Sr₂Ca₆Fe ₃ ²⁺ Zr₃NbSi₂₅O₇₂(OH,O)₄Cl(Н₂О)_0.2. The chemical composition and structure of this mineral are close to those of taseqite; however, it differs from the holotype sample by a low chlorine content and peculiarities of cation distribution over basic structure sites. A comparative analysis of strontium-rich eudialytes has revealed their important crystallochemical feature: selective concentration of strontium in the N4 site. Thus, taseqite, along with heterophyllosilicates, may play a role of strontium concentrator in agpaitic pegmatites.     

Crystal Structure of the First Representative of the Eudialyte Group with Primitive Unit Cell

Crystallography Reports - The first representative of the eudialyte group with a primitive unit cell has been investigated by X-ray diffraction analysis, electron probe microanalysis, and IR...     

Perovskites with the Framework‐Forming Xenon

The Group 18 elements (noble gases) were the last ones in the periodic system to have not been encountered in perovskite structures. We herein report the synthesis of a new group of double perovskites KM(XeNaO₆) (M=Ca, Sr, Ba) containing framework‐forming xenon. The structures of the new compounds, like other double perovskites, are built up of the alternating sequence of corner‐sharing (XeO₆) and (NaO₆) octahedra arranged in a three‐dimensional rocksalt order. The fact that xenon can be incorporated into the perovskite structure provides new insights into the problem of Xe depletion in the atmosphere. Since octahedrally coordinated Xe^VIII and Si^IV exhibit close values of ionic radii (0.48 and 0.40 Å, respectively), one could assume that Xe^VIII can be incorporated into hyperbaric frameworks such as MgSiO₃ perovskite. The ability of Xe to form stable inorganic frameworks can further extend the rich and still enigmatic chemistry of this noble gas.     

Thermal decomposition of 2,4-diazido-6-trinitromethyl-1,3,5-triazine, 2,4-dimethoxy-6-trinitromethyl-1,3,5-triazine,and 2,4-diazido-6-methoxy-1,3,5-triazine

The thermal decomposition of 2,4-diazido-6-trinitromethyl-1,3,5-triazine, 2,4-dimethoxy-6-trinitromethyl-1,3,5-triazine, and 2,4-diazido-6-methoxy-1,3,5-triazine in a melt was studied by differential scanning calorimetry, thermogravimetry, manometry, mass spectrometry, and IR spectroscopy. The kinetics of these reactions was investigated, and the activation parameters were determined. The gaseous products of the decomposition of 6-trinitromethyl-2,4-diazido-1,3,5-triazine were N₂, NO, N₂O, CO, and CO₂ in a molar ratio of 1: 2: 1: 0.6: 1 and pronounced amounts of NO₂. A comparison of kinetic data for the compounds under study indicated that the azide groups in 2,4-diazido-6-trinitromethyl-1,3,5-triazine were thermally more stable than the trinitromethyl group.     

Synthetic calcium aluminosilicate monolith: III. The nature of binder and high-temperature behavior

We have studied the physicochemical properites of the SCAS monolith that was manufactured from fly ash (a large-tonnage waste of coal dust combustion at power plants), lime, and sand in a three-stage process comprising the stages of filtration combustion with superadiabatic heating, fine milling, and pressing, and then hardened in natural (laboratory) settings for 7 years. From the inspection of IR spectra together with the results of energy dispersive X-ray microanalysis, we discovered that calcium serpentine (Ca,Fe,Mg)₃[(Si,Al)₂O₅](OH,H₂O)₄ was formed in the SCAS monolith during 7-year natural hydration/carbonization, this serpentine acting as a binder in the dispersion-hardened polymineral body. This inference matches the results obtained by X-ray powder diffraction. Differential scanning calorimetry/thermogravimetry (DSC/TGA) with simultaneous recording of the mass spectra of the products has been used to study dehydration, dehydroxylation, decarbonization, and recrystallization occurring in the SCAS monolith between 35 and 1000°C. We have demonstrated that the calcium carbonate polymorphs contained in the monolith have a reduced thermal destruction temperature. The tetrahedral calcium serpentine layer has not been destroyed as a result of heating to 1000°C.     

2,4,6-Triazido-1,3,5-Triazine, 2,4,6-Triazidopyrimidine,and 2,4,6-Triazidopyridine as Precursors of Carbon Nitride Materials

The thermolysis of 2,4,6-triazido-1,3,5-triazine (I), 2,4,6-triazidopyrimidine (II), and 2,4,6-triazidopyridine (III) and its products were studied by DSC, mass spectrometry, IR spectroscopy, and electron microscopy. The thermal transformations of I gave planar nets formed by polyconjugated C–N bonds arranged into bundle aggregates. The thermolysis product of III consists of low-molecular compounds and has globular morphology. The thermolysis of II resulted in a mixture of products of both types, among which the planar nets were dominant. The relationship between the structure of the products of the thermal transformations of I, II, and III and the kinetic characteristics of these processes was discussed.     

Prephase state in 2-bromo-2-nitropropane-1,3-diol crystals: Structural aspects and IR spectra

This paper is a continuation of our series of publications dealing with crystal-lattice processes occuning on heating and at temperatures near the transition point and accompanied by structural changes in discrete molecules and in the crystal structure as a whole. The prephase state of 2-bromo-2-nitropropane-1,3-diol crystals and the transition from monoclinic to cubic phase are studied by IR spectroscopy at 296–391 K. Translated fromZnumal Strktumo, Chimii, Vol. 41, No. 2, pp. 294–299, March–April, 2000.