Polyoxometalate chemistry at volcanoes: discovery of a novel class of polyoxocuprate nanoclusters in fumarolic minerals

Polyoxometalate (POM) chemistry is an important avenue of comprehensive chemical research, due to the broad chemical, topological and structural variations of multinuclear polyoxoanions that result in advanced functionality of their derivatives. The majority of compounds in the polyoxometalate kingdom are synthesized under laboratory conditions. However, Nature has its own labs with the conditions often unconceivable to the mankind. The striking example of such a unique environment is volcanic fumaroles – the natural factories of gas-transport synthesis. We herein report on the discovery of a novel class of complex polyoxocuprates grown in the hot active fumaroles of the Tolbachik volcano at the Kamchatka Peninsula, Russia. The cuboctahedral nanoclusters {[MCu$_{12}$O$_{8}$](AsO$_{4}$)$_{8}$} are stabilized by the core Fe(III) or Ti(IV) cations residing in the unique cubic coordination. The nanoclusters are uniformly dispersed over the anion- and cation-deficient NaCl matrix. Our discovery might have promising implications for synthetic chemistry, indicating the possibility of preparation of complex polyoxocuprates by chemical vapor transport (CVT) techniques that emulate formation of minerals in high-temperature volcanic fumaroles

Ellinaite, CaCr2O4, a New Natural Post-Spinel Oxide from Hatrurim Basin, Israel, and Juína Kimberlite Field, Brazil

Ellinaite, a natural analog of the post-spinel phase β-CaCr2O4, was discovered at the Hatrurim Basin, Hatrurim pyrometamorphic formation (the Mottled Zone), Israel, and in an inclusion within the super-deep diamond collected at the placer of the Sorriso River, Juína kimberlite field, Brazil. Ellinaite at the Hatrurim Basin is confined to a reduced rankinite-gehlenite paralava, where it occurs as subhedral grains up to 30μm in association with gehlenite, rankinite and pyrrhotite or forms the rims overgrowing zoned chromite-magnesiochromite. The empirical formula of the Hatrurim sample is (Ca0.960Fe0.0162+Na0.012Mg0.003)0.992(Cr1.731V0.1833+Ti0.0683+Al0.023Ti0.0034+)2.008O4. The mineral crystallizes in the orthorhombic system, space group Pnma, unit-cell parameters refined from X-ray single-crystal data: A 8.868(9), b 2.885(3), c 10.355(11)Å, V 264.9(5)Å3 and ZCombining double low line4. The crystal structure of ellinaite from the Hatrurim Basin has been solved and refined to R1Combining double low line0.0588 based on 388 independent observed reflections. Ellinaite in the Juína diamond occurs within the micron-sized polyphase inclusion in association with ferropericlase, magnesioferrite, orthorhombic MgCr2O4, unidentified iron carbide and graphite. Its empirical formula is Ca1.07(Cr1.71Fe0.063+V0.06Ti0.03Al0.03Mg0.02Mn0.02)ς1.93O4. The unit-cell parameters obtained from HRTEM data are as follows: Space group Pnma, a 9.017, b 2.874Å, c 10.170Å, V 263.55Å3, ZCombining double low line4. Ellinaite belongs to a group of natural tunnel-structured oxides of the general formula AB2O4, the so-called post-spinel minerals: Marokite CaMn2O4, xieite FeCr2O4, harmunite CaFe2O4, wernerkrauseite CaFe23+Mn4+O6, chenmingite FeCr2O4, maohokite MgFe2O4 and tschaunerite Fe(FeTi)O4. The mineral from both occurrences seems to be crystallized under highly reduced conditions at high temperatures (>1000°C), but under different pressure: Near-surface (Hatrurim Basin) and lower mantle (Juína diamond). © 2021 Victor V. Sharygin et al.Raman spectroscopy and EBSD investigations for the Hatrurim ellinaite were done on state assignment of IGM SB RAS (IX.125.2) and the Initiative Project of Ministry of Science and Higher Education of the Russian Federation (Act 211 of the Government of the Russian Federation (grant agreement no. 02.A03.21.0006)). SEM and microprobe studies for the Hatrurim ellinaite were supported by the Russian Science Foundation (grant no. 17-17-01056p). Crystallographic studies of the Hatrurim ellinaite were provided by the Russian Science Foundation (grant no. 18-17-00079)

Unusual silicate mineralization in fumarolic sublimates of the Tolbachik volcano, Kamchatka, Russia – Part 2: Tectosilicates

This second of two companion articles devoted to silicate mineralization in fumaroles of the Tolbachik volcano (Kamchatka, Russia) reports data on chemistry, crystal chemistry and occurrence of tectosilicates: sanidine, anorthoclase, ferrisanidine, albite, anorthite, barium feldspar, leucite, nepheline, kalsilite, sodalite and hauyne. Chemical and genetic features of fumarolic silicates are also summarized and discussed. These minerals are typically enriched with “ore” elements (As, Cu, Zn, Sn, Mo, W). Significant admixture of As5+ (up to 36&thinsp;wt&thinsp;% As2O5 in sanidine) substituting Si is the most characteristic. Hauyne contains up to 4.2&thinsp;wt&thinsp;% MoO3 and up to 1.7&thinsp;wt&thinsp;% WO3. All studied silicates are hydrogen-free, including mica and amphiboles which are F-rich. Iron-bearing minerals contain only Fe3+ due to strongly oxidizing formation conditions. In Tolbachik fumaroles, silicates were formed in the temperature range 500–800&thinsp;∘C as a result of direct deposition from the gas phase (as volcanic sublimates) or gas–rock interactions. The zonation in distribution of major silicate minerals observed in a vertical section of the Arsenatnaya fumarole, from deep (the hottest) to upper parts is diopside + forsterite + enstatite + andradite → diopside → fluorophlogopite + diopside → sanidine + fluorophlogopite → sanidine. This is in agreement with volatilities of major species-defining metals in volcanic gases. From a crystal-chemical viewpoint, this series corresponds to the following sequence of crystallization of minerals with temperature decrease: nesosilicates → inosilicates → phyllosilicates → tectosilicates.</p

Unusual silicate mineralization in fumarolic sublimates of the Tolbachik volcano, Kamchatka, Russia – Part 1: Neso-, cyclo-, ino- and phyllosilicates

This is the initial paper in a pair of articles devoted to silicate minerals from fumaroles of the Tolbachik volcano (Kamchatka, Russia). These papers contain the first systematic data on silicate mineralization of fumarolic genesis. In this article nesosilicates (forsterite, andradite and titanite), cyclosilicate (a Cu,Zn-rich analogue of roedderite), inosilicates (enstatite, clinoenstatite, diopside, aegirine, aegirine-augite, esseneite, “Cu,Mg-pyroxene”, wollastonite, potassic-fluoro-magnesio-arfvedsonite, potassic-fluoro-richterite and litidionite) and phyllosilicates (fluorophlogopite, yanzhuminite, “fluoreastonite” and the Sn analogue of dalyite) are characterized with a focus on chemistry, crystal-chemical features and occurrence. Unusual As5+-rich varieties of forsterite, andradite, titanite, pyroxenes, amphiboles and mica are described. General data on silicate-bearing active fumaroles and the diversity and distribution of silicates in fumarole deposits are reported. Evidence for the fumarolic origin of silicate mineralization is discussed.</p

Alumoåkermanite, (Ca,Na)₂(Al,Mg,Fe²⁺)(Si₂O₇), a new mineral from the active carbonatite-nephelinite-phonolite volcano Oldoinyo Lengai, northern Tanzania

Alumoåkermanite, (CaNa)₂(Al,Mg,Fe²⁺)(Si₂O₇), is a new mineral member of the melilite group from the active carbonatite-nephelinite-phonolite volcano Oldoinyo Lengai, Tanzania. The mineral occurs as tabular phenocrysts and microphenocrysts in melilite-nephelinitic ashes and lapilli-tuffs. Alumoåkermanite is light brown in colour; it is transparent, with a vitreous lustre and the streak is white. Cleavages or partings are not observed. The mineral is brittle with an uneven fracture. The measured density is 2.96(2) g/cm³. The Mohs hardness is ∼4.5-6. Alumoåkermanite is uniaxial (-) with ω = 1.635(1) and ε = 1.624-1.626(1). In a 30 μm thin section (+N), the mineral has a yellow to orange interference colour, straight extinction and positive elongation, and is nonpleochroic. The average chemical formula of the mineral derived from electron microprobe analyses is: (Ca1.48Na0.50Sr0.02K0.01)Σ2.01(Al0.44Mg0.30Fe²⁺0.17Fe³⁺0.07Mn0.01)Σ0.99(Si1.99Al0.01O₇). Alumoåkermanite is tetragonal, space group P42₁m with a = 7.7661(4) Å, c = 5.0297(4) Å, V = 303.4(1) ų and Z = 2. The five strongest powder-diffraction lines [d in Å, (I/Io), hkl] are: 3.712, (13), (111); 3.075, (25), (201); 2.859, (100), (211); 2.456, (32), (311); 1.757, (19), (312). Single-crystal structure refinement (R₁ = 0.018) revealed structure topology typical of the melilite-group minerals, i.e. tetrahedral [(Al,Mg)(Si₂O₇)] sheets interleaved with layers of (CaNa) cations. The name reflects the chemical composition of the mineral

Layered Hydrazinium Titanate: Advanced Reductive Adsorbent and Chemical Toolkit for Design of Titanium Dioxide Nanomaterials

LHT-9, a layered hydrazinium titanate with an interlayer spacing of ~9 Å, is a new nanohybrid compound combining the redox functionality of hydrazine, the ion-exchange properties of layered titanate, the large surface area of quasi-two-dimensional crystallites, surface Brønsted acidity, and the occurrence of surface titanyl bonds. LHT-9, ideally formulated as (N(2)H(5))(1/2)Ti(1.87)O(4), relates to a family of lepidocrocite-type titanates. It possesses a high uptake capacity of ~50 elements of the periodic table. Irreversibility of reductive adsorption allows LHT-9 to be used for cumulative extraction of reducible moieties (noble metals, chromate, mercury, etc.) from industrial solutions and wastewaters. Unlike sodium titanates that do not tolerate an acidic environment, LHT-9 is capable of uptake of transition metals and lanthanides at pH > 3. Adsorption products loaded with the desired elements retain their layered structures and can be used as precursors for tailored titanium dioxide nanomaterials. In this respect, the uptake of metal ions by LHT-9 can be considered as a method complementary to electrostatic self-assembly deposition (ESD) and layer-by-layer self-assembly (LBL) techniques. LHT-9 is readily synthesized in one step by a mild fluoride route involving hydrazine-induced hydrolysis of hexafluorotitanic acid under near-ambient conditions

Water-soluble carbonyl complexes of 99Tc(I) and Re(I) with adamantane-cage aminophosphines PTA and CAP

Pentacarbonyl complexes of 99Tc and Re [M(CAP)(CO)5]X and [M(PTA)(CO)5]X (M = 99Tc or Re and X = ClO4− or OTf–) with aminophosphine ligands 1,4,7-triaza-9-phosphatricyclo[5.3.214,9]tridecane (CAP) and 1,3,5-triaza-7-phosphaadamantane (PTA) were prepared for the first time by the reaction of [MX(CO)5] (M = 99Tc or Re, X = ClO4− or OTf–) with CAP and PTA in CH2Cl2 at room temperature. The reaction of [TcCl(CO)5] with CAP in refluxing CH2Cl2 yields the tricarbonyl complex [99TcCl(CAP)2(CO)3]. Treatment of [Re(H2O)3(CO)3]Cl with CAP in aqueous solution at 40–50 °C gives the rhenium analog [ReCl(CAP)2(CO)3]. Both penta- and tricarbonyl phosphine complexes were characterized by spectroscopic methods (IR, NMR, MS) and single crystal X-ray diffraction. The [M(PTA)(CO)5]X complexes are soluble in aqueous solutions, whereas their CAP analogs are not. The CAP complexes become water-soluble after acidification with dilute acids. As the pH of their aqueous solutions increases, they start to slowly degrade at pH 8 and completely decompose at pH 14. In acidic media, the pentacarbonyl complexes undergo stepwise protonation and are stable indefinitely

Crystallographic Insights into Uranyl Sulfate Minerals Formation: Synthesis and Crystal Structures of Three Novel Cesium Uranyl Sulfates

An alteration of the uranyl oxide hydroxy-hydrate mineral schoepite [(UO2)8O2(OH)12](H2O)12 at mild hydrothermal conditions was studied. As the result, four different crystalline phases Cs[(UO2)(SO4)(OH)](H2O)0.25 (1), Cs3[(UO2)4(SO4)2O3(OH)](H2O)3 (2), Cs6[(UO2)2(SO4)5](H2O)3 (3), and Cs2[(UO2)(SO4)2] (4) were obtained, including three novel compounds. The obtained Cs uranyl sulfate compounds 1, 3, and 4 were analyzed using single-crystal XRD, EDX, as well as topological analysis and information-based structural complexity measures. The crystal structure of 3 was based on the 1D complex, the topology of which was unprecedented for the structural chemistry of inorganic oxysalts. Crystal chemical analysis performed herein suggested that the majority of the uranyl sulfates minerals were grown from heated solutions, and the temperature range could be assumed from the manner of interpolyhedral linkage. The presence of edge-sharing uranyl bipyramids most likely pointed to the temperatures of higher than 100 &deg;C. The linkage of sulfate tetrahedra with uranyl polyhedra through the common edges involved elevated temperatures but of lower values (~70&ndash;100 &deg;C). Complexity parameters of the synthetic compounds were generally lower than that of uranyl sulfate minerals, whose structures were based on the complexes with the same or genetically similar topologies. The topological complexity of the uranyl sulfate structural units contributed the major portion to the overall complexity of the synthesized compounds, while the complexity of the respective minerals was largely governed by the interstitial structure and H-bonding system