Heterogeneous H2O2-based selective oxidations over zirconium tungstate α-ZrW2O8.

Catalytic properties of a crystalline zirconium tungstate, ZrW2O8, the material known mainly for its isotropic negative coefficient of thermal expansion, have been assessed for the liquid-phase selective oxidation of a range of organic substrates comprising CC, OH, S and other functional groups using aqueous hydrogen peroxide as the green oxidant. Samples of ZrW2O8 were prepared by hydrothermal synthesis and characterised by N2 adsorption, PXRD, SEM, EDX, FTIR and Raman spectroscopic techniques. Studies by IR spectroscopy of adsorbed probe molecules (CO and CDCl3) revealed the presence of Brønsted acidic and basic sites on the surface of ZrW2O8. It was demonstrated that ZrW2O8 is able to activate H2O2 under mild conditions and accomplish the epoxidation of CC bonds in alkenes and unsaturated ketones, oxidation of thioethers to sulfoxides and sulfones, along with the oxidation of alcoholic functions to produce ketones and aldehydes. The oxidation of tetramethylethylene and α-terpinene over ZrW2O8 revealed the formation of peroxidation products, 2,3-dimethyl-3-butene-2-hydroperoxide and endoperoxide ascaridole, respectively, indicating the involvement of singlet oxygen in the oxidation process. The ZrW2O8 catalyst preserves its structure and morphology under the turnover conditions and does not suffer from metal leaching. It can be easily recovered, regenerated by calcination, and reused without the loss of activity and selectivity.

Revisiting Sodium Hexafluoroiridates: Perspective Precursors for Electronic, Quantum, and Related Materials.

The following salts have been synthesized and structurally characterized: Na2[IrF6]·2H2O (C2/m, a = 6.6327(4), b = 10.0740(6), c = 5.9283(5) Å, ß = 122.3880(10)°) and Na3[IrF6]·2H2O (R-3, a = 7.5963(3), b = 7.5963(3), c = 9.8056(4) Å) (for the first time) by single-crystal X-ray diffraction; the unit cell parameters of a tetragonal phase (P4 2/mnm, a = 5.005(2), c = 10.074(4) Å) of the stable α-Na2[IrF6] were determined for the first time; and the unit cell parameters of ß-Na2[IrF6] (P321, a = 9.332(4), c = 5.136(2) Å) and Na3[IrF6] (P21/n, a = 5.567(4), b = 5.778(4), c = 8.017(2) Å, ß = 90.41(2)°) were determined using powder X-ray diffraction (PXRD). The data of the thermal stability was obtained by differential thermal analysis (DTA) for all substances. The presence of Na3[IrF6]·H2O monohydrate is predicted. H2[IrF6] was prepared in a solution and was demonstrated to behave as a strong dibasic acid.

Insight into the thermal decomposition of ammonium hexahalogenoiridates(IV) and hexachloroiridate(III).

Thermal decomposition of (NH4)3[IrCl6]·H2O, (NH4)2[IrCl6] and (NH4)2[IrBr6] in reductive and inert atmospheres has been investigated in situ using quick-EXAFS and temperature-resolved powder X-ray diffraction. For the first time, (NH4)2[Ir(NH3)Cl5] and (NH4)2[Ir(NH3)Br5] have been proven as intermediates of thermal decomposition of (NH4)3[IrCl6]·H2O, (NH4)2[IrCl6] and (NH4)2[IrBr6]. Thermal degradation of (NH4)2[IrCl6] and (NH4)2[IrBr6] is a more complex process as suggested previously and includes simultaneous formation of (NH4)2[Ir(NH3)Cl5] and (NH4)2[Ir(NH3)Br5] intermediates mixed with metallic iridium. In the inert atmosphere, complexes (NH4)[Ir(NH3)2Cl4] and (NH4)[Ir(NH3)2Br4] as well as [Ir(NH3)3Br3] were proposed as possible intermediates before formation of metallic iridium particles.

Preparation of Zr(Mo,W)2O8 with a larger negative thermal expansion by controlling the thermal decomposition of Zr(Mo,W)2(OH,Cl)2∙2H2O.

Solid solutions of Zr(Mo,W)2O7(OH,Cl)2∙2H2O with a preset ratio of components were prepared by a hydrothermal method. The chemical composition of the solutions was determined by energy dispersive X-ray spectroscopy (EDX). For all the samples of ZrMoxW2-xO7(OH,Cl)2∙2H2O (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0), TGA and in situ powder X-ray diffraction (PXRD) studies (300-1100 K) were conducted. For each case, the boundaries of the transformations were determined: Zr(Mo,W)2O7(OH,Cl)2∙2H2O → orthorhombic-ZrMoxW2-xO8 (425-525 K), orthorhombic-ZrMoxW2-xO8 → cubic-ZrMoxW2-xO8 (700-850 K), cubic-ZrMoxW2-xO8 → trigonal-ZrMoxW2-xO8 (800-1050 K for x > 1) and cubic-ZrMoxW2-xO8 → oxides (1000-1075 K for x ≤ 1). The cell parameters of the disordered cubic-ZrMoxW2-xO8 (space group Pa-3) were measured within 300-900 K, and the thermal expansion coefficients were calculated: -3.5∙10-6 - -4.5∙10-6 K-1. For the ordered ZrMo1.8W0.2O8 (space group P213), a negative thermal expansion (NTE) coefficient -9.6∙10-6 K-1 (300-400 K) was calculated. Orthorhombic-ZrW2O8 is formed upon the decomposition of ZrW2O7(OH,Cl)2∙2H2O within 500-800 K.

Three hexafluoridoiridates(IV), Ca[IrF6].2H2O, Sr[IrF6].2H2O and Ba[IrF6].

The structures of the hexafluoridoiridates(IV) of calcium, Ca[IrF(6)].2H(2)O [calcium hexafluoridoiridate(IV) dihydrate], strontium, Sr[IrF(6)].2H(2)O [strontium hexafluoridoiridate(IV) dihydrate], and barium, Ba[IrF(6)] [barium hexafluoridoiridate(IV)], have been determined by single-crystal X-ray analysis. The first two compounds are isomorphous. Their metal cations are eight-coordinated in a distorted square-antiprismatic coordination environment, and their anions are represented by an almost ideal octahedron. These two structures can be described as frameworks in which all atoms occupy general positions. Sr[RhF(6)] and Ba[RhF(6)] have a different space group (R\overline{3}m, from powder diffraction data) but similar cell dimensions. The structures are very close to that of Ba[IrF(6)]. The cation is in a cuboctahedral coordination. The metal atoms are located on special positions of \overline{3} symmetry, while the F atoms are in general positions.

Double complexes [Co(NH(3))(5)(H(2)O)](2)[Zr(3)F(18)].6H(2)O and [Co(NH(3))(6)](2)[Zr(3)F(18)].6H(2)O.

The structures of orthorhombic bis[pentaammineaquacobalt(III)] tetra-mu(2)-fluorido-tetradecafluoridotrizirconium(IV) hexahydrate (space group Ibam), [Co(NH(3))(5)(H(2)O)](2)[Zr(3)F(18)].6H(2)O, (I), and bis[hexaamminecobalt(III)] tetra-mu(2)-fluorido-tetradecafluoridotrizirconium(IV) hexahydrate (space group Pnna), [Co(NH(3))(6)](2)[Zr(3)F(18)].6H(2)O, (II), consist of complex [Co(NH(3))(x)(H(2)O)(y)](3+) cations with either m [in (I)] or overline{1} and 2 [in (II)] symmetry, [Zr(3)F(18)](6-) anionic chains located on sites with 222 [in (I)] or 2 [in (II)] symmetry, and water molecules.