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Solid Solution Formation between Vanadium(V) and Tungsten(V) Oxide Phosphate



The solid solutions (V1–xWx)OPO4 with β-VOPO4 structure type (0.0≤x≤0.01) and αII-VOPO4 structure type (0.04≤x≤0.26) were obtained from mixtures of VVOPO4 and WVOPO4 by conventional solid state reactions and by solution combustion synthesis. Single crystals of up to 3 mm edge length were obtained by chemical vapor transport (CVT) (800 [RIGHTWARDS ARROW] 700 °C, Cl2 as a transporting agent). Single crystal structure refinements of crystals at x=0.10 [a=6.0503(2) Å, c=4.3618(4) Å, R1=0.021, wR2=0.058, 21 parameters, 344 independent reflections] and x=0.26 [a=6.0979(2) Å, c=4.2995(1) Å, R1=0.030, wR2=0.081, 21 parameters, 346 independent reflections] confirm the αII-VOPO4 structure type (P4/n, Z=2) with mixed occupancy V/W for the metal site. Due to the specific redox behavior of W5+ and V5+, solid solutions (V1–xWx)OPO4 should be formulated as (VIVxVV1–2xWVIx)OPO4. The valence states of vanadium and tungsten are confirmed by XPS measurements. V4+ with d1 configuration was identified by EPR spectroscopy and magnetic measurements. Electronic spectra of the solid solutions show the IVCT(V4+ → V5+) and the LMCT(O2- → V5+). (V0.74W0.26)OPO4 powders exhibit semi-conducting behavior (Eg=0.7 eV).



Lithium Copper(I) Orthophosphates Li3–xCuxPO4: Synthesis, Crystal Structures and Electrochemical Properties



Along the quasi-binary section Li3PO4 - CuI3PO4 three different phases Li3–xCuIxPO4 each with extended homogeneity range occur under equilibrium conditions (650≤ϑ≤700 °C). According to single-crystal X-ray structure analyses Phase 1 (0<x≤0.7) adopts the HT- or β-Li3PO4 structure type [Li2.6CuI0.4PO4, Pnma (no. 62), Z=4, a=10.4612(2) Å, b=6.1690(3) Å, c=4.9854(2) Å, R1=0.023, wR2=0.062, Goof=1.12] and Phase 2 (0.9≤x≤1.8) is isotypic to LT- or α-Li3PO4 [Li2.05CuI0.95PO4, Pnm21 (no. 31), Z=2, a=6.2113(8) Å, b=5.2597(7) Å, c=4.9904(5) Å, R1=0.040, wR2=0.108, Goof=0.98]. A preliminary structure model for the copper-rich Phase 3 (2.1≤x≤2.8) ["Li0.6CuI2.4PO4", P3 (no. 147), a=6.223(1) Å, c=5.3629(5) Å] could be refined to R1=0.07. Sharp 31P-MAS-NMR resonances observed in the spectra of Li2.6CuI0.4PO4 (δiso=10.4 ppm), Li2.05CuI0.95PO4 (δiso=12.4 ppm), and Li0.84CuI2.16PO4 (δiso=10.9 ppm) provide evidence for the absence of paramagnetic Cu2+ ions. Pure copper(I) orthophosphate CuI3(PO4) exists as a homogeneous melt (≥800 °C) and can be obtained as thermodynamically metastable solid by quenching. It is isotypic to Phase 3 [a=6.284(3) Å, c=5.408(5) Å]. Electrochemical delithiation of Li2.05CuI0.95PO4 (C/10, C/30) indicates two partially reversible oxidation processes between 3.75 V and 4.80 V (vs. Li0/Li+).



Chemical Vapor Transport Reactions - A Historical Review



In Memoriam of Professor Harald Schäfer on the Occasion of His 100th Anniversary

Since their first recognition in mineral forming processes some 150 years ago chemical vapor transport reactions (CVTR) have attracted continuous scientific interest. Due to the pioneering work of Harald Schäfer quantitative understanding and exploitation of transport reactions for crystal growth, synthesis, investigation of high-temperature gas species, and thermodynamic studies have become possible. Renewed interest in CVT is triggered by the demand of material sciences for novel compounds with tailor-made physical properties and by the need for efficient recycling strategies for various metals from industrial waste.



Equilibrium relations in the system TiO2/V2O5/P2O5 and crystal structure of a NASICON-related vanadyl(V) titanium(IV) phosphate



Vanadyl(V)-titanium-orthophosphate (VVO)TiIV6(PO4)9 is formed by solid state reactions in the temperature range 525≤ϑ≤780 °C. At higher temperature decomposition into V2O5 and the hitherto unknown solid solution Ti(P1−xVx)2O7 (0≤x≤0.23; 0.30≤x≤0.43) is observed. The process of phase formation has been monitored by MAS-NMR (31P, 51V) spectroscopy. Equilibrium phase relations in the quaternary system TiO2/VO2.5/PO2.5 have been determined.
A structure analysis from X-ray single-crystal data (P63/m (No. 176), Z=2; a=8.4438(3) Å, c=22.215(1) Å, 14 independent atoms, 87 variables, 2066 unique reflections, R1=0.032, wR2=0.084) shows the relationship of (VVO)TiIV6(PO4)9 to the NASICON structure family. In marked contrast to the other members of this family [TiIV2O9] double-octahedra and strongly distorted tetrahedral [(VV=O)O3] groups are observed besides isolated [TiIVO6] octahedra and phosphate tetrahedra. The structure model is in agreement with the results from MAS-NMR (31P, 51V) spectroscopy.



Searching for “LiCrIIPO4



The two new phosphates LiCrII4(PO4)3 and Li5CrII2CrIII(PO4)4 are discovered as equilibrium phases (ϑ=800 °C) in the quarternary system Li/Cr/P/O. Their crystal structures have been determined from single-crystal X-ray diffraction data {LiCrII4(PO4)3: violet-blue, Pnma (no. 62), Z=4, a=6.175(1) Å, b=14.316(3) Å, c=10.277(2) Å, 100 parameters, R1=0.028, wR2=0.08, 2060 unique reflections with Fo>4σ(Fo); Li5CrII2CrIII(PO4)4: greyish-green, P1 (no. 2), Z=1, a=4.9379(7) Å, b=7.917(2) Å, c=8.426(2) Å, α=109.98(2)°, β=90.71(1)°, γ=104.91(1)°, 131 parameters, R1=0.022, wR2=0.067, 1594 unique reflections with Fo>4σ(Fo)}. Li5CrII2CrIII(PO4)4 adopts an hitherto unknown structure type. The crystal structure of LiCrII4(PO4)3 is isotypic to that of NaCdII4(PO4)3 and related to that of the mineral silicocarnotite Ca5(PO4)2(SiO4). Significant disorder between Li+ and Cr2+ is observed for both crystal structures. The oxidation states assigned to chromium in these two phosphates are in agreement with UV/vis/NIR absorption spectra and magnetic susceptibility data recorded for both compounds.
Instead of "LiCrIIPO4" mixtures of LiCrII4(PO4)3, Li5CrII2CrIII(PO4)4, Cr2O3, and CrP are observed at equilibrium. Instead of "Li2CrIIP2O7" four-phase mixtures consisting of Li9CrIII3(P2O7)3(PO4)2, Li3CrIII2(PO4)3, LiCrP2O7, and CrP were obtained.



The First Phosphates of Heptavalent Rhenium


101ReVIIO2(PO4) and (ReVII2O5)Sio2[Sit2O(PO4)6] were obtained from Re2O7 and P4O10 in sealed silica tubes (250≤ϑ≤400 °C). The crystal structures were solved and refined from X-ray single crystal data (ReVIIO2(PO4): C2/c, Z=24, a=14.403(1) Å, b=8.414(1) Å, c=20.647(3) Å, β=93.165(8)°, T=123 K, 10352 ind. refl., 218 variables, 24 atoms in asymmetric unit, R1=0.041, wR2=0.106; (ReVII2O5)Sio2[Sit2O(PO4)6]: P1, Z=1, a=7.8589(3) Å, b=7.8609(3) Å, c=10.8311(4) Å, α=85.312(2)°, β=73.078(2)°, γ=60.075(2)°, T=298 K, 2551 ind. reflections, 174 variables, 22 atoms in asymmetric unit, R1=0.078, wR2=0.208). The complex crystal structure of ReO2(PO4) can be derived from the ReO3 structure type. The crystal structure of the silicophosphate consists of distorted [Re2O11] dioctahedra (1.69 Å ≤ d(Re–O) ≤ 2.08 Å), [SiIVO6] octahedra, and [Sit2O(PO4)6]12– heteropolyanions. In ReO2(PO4) monomeric perrhenyl ions (ReO2)3+ (<(Ot,Re,Ot) ≈ 101.5°) are formed. The silicophosphate (Re2O5)Sio2[Sit2O(PO4)6] contains dinuclear (Re2O5)4+ cations. 31P-MAS-NMR studies on ReO2(PO4) are in accordance with three independent sites of phosphorus. The results of 31P- and 29Si-MAS-NMR studies on (Re2O5)Sio2[Sit2O(PO4)6] are in agreement with three crystallographically independent sites for phosphorus and two sites for silicon.



Chemische Transportreaktionen / Chemical Vapor Reactions


Chemische TransportreaktionenChemical Vapor ReactionsChemische Transportreaktionen weisen ein gemeinsames Merkmal auf: In Gegenwart eines gasförmigen Reaktionspartners, des Transportmittels, wird eine feste oder flüssige Komponente verflüchtigt. An anderer Stelle scheidet sie sich meist in Form gut ausgebildeter Kristalle wieder ab. So ist der Chemische Transport z. B. für den Festkörperchemiker ein unentbehrliches Verfahren zur Herstellung reiner, gut kristallisierter Feststoffe.
Als umfassendes Handbuch behandelt dieses Werk die vielseitigen Aspekte von Chemischen Transportreaktionen: Von der Grundlagenforschung bis hin zur praktischen Bedeutung, beispielsweise für die Funktionsweise von Halogenlampen.

  • Umfassendes Handbuch zum Thema Chemische Transportreaktionen
  • Grundlagen, Modelle und Verfahren z. B. zum Chemischen Transport von Metallhalogeniden, binären und polynären Oxiden, Sulfiden, Seleniden und Telluriden sowie zur Herstellung von Einkristallen für Kristallstrukturanalysen
  • Klar strukturierte Übersichten und ausführliche Tabellen mit Beispielen aus der Literatur
  • Zusätzliche Information zu thermodynamischen Daten, Modellierungsmöglichkeiten, Arbeitstechniken und ausgewählten Experimenten
  • Farbtafeln mit Kristallabbildungen

This comprehensive handbook covers the diverse aspects of chemical transport reactions from basic research to important practical applications, for instance how halogen lamps function.

  • A comprehensive manual on the topic of chemical transport reactions
  • An indispensable synthesis method for the solid-state chemist
  • An important method for producing single crystals for crystal structure analysis and the basis for how halogen lamps function; use in metal puri-fication and material coating
  • Clearly structured overviews and detailed tables with examples from the literature for the chemical transport of halogenides, binary and polynary oxides, sulfides, selenides and tellurides, chalcogenide halogenides, pnic-tides
  • Additional information on thermodynamic data, modeling possibilities, work techniques and selected experiments related to the topic of chemical transport



Network Formation by Square-planes and Tetrahedra: Polynary Palladiumphosphates MPd2(PO4)2 (M = Ca, Cd, Hg), MPdP2O7 (M = Ca, Sr, Ba, Zn, Hg, Pb) and PbPdSi(P2O7)2


90 Starting from PdO, HgO and P4O10 yellow, plate-like single crystals of HgPdP2O7 were obtained by chemical vapour transport experiments (600 °C → 500 °C, addition of PdCl2). Micro-crystalline PbPdP2O7 is synthesized by heating (Tmax=700 °C) stoichiometric amounts of PdO, PbO, and phosphoric acid. Using chemical vapour transport experiments (800 °C → 700 °C, addition of PdCl2) brown plate-like single crystals of PbPdP2O7 were obtained besides yellow needles of PbPdSi(P2O7)2. Brown, prismatic crystals of HgPd2(PO4)2 with edge-lengths up to 1 mm were grown by solvothermal reactions of PdO and HgO with conc. H3PO4 (400 °C, 7d, cooling: 1°/h). The structures of all compounds were determined and refined from X-ray single crystal data (HgPdP2O7: C2/c, a=14.117(2) Å, b=4.884(1) Å,c=8.802(1) Å, β=100.9(1)°; PbPdP2O7: Pnma, a=13.440(1) Å, b=5.966(1) Å, c=7.368(1) Å; PbPdSi(P2O7)2: P21/m, a=4.593(1) Å, b=17.169(1) Å, c=6.435(1) Å, β=101.71(1)°; HgPd2(PO4)2: Fddd, a=6.955(1) Å, b=11.342(1) Å, c=15.840(1) Å). According to IP Guinier-photographs microcrystalline powders of MPd2(PO4)2 (M = Cd, Ca) and MPdP2O7 (M = Ca, Sr, Ba, Zn) are isotypic to HgPd2(PO4)2 and PbPdP2O7, respectively. 31P-MAS-NMR studies on HgPdP2O7 and CaPd2(PO4)2 are in accordance with one independent site for phosphorus. Their chemical shifts were determined to δiso=24.2, δaniso=83.0, η=0.43 for HgPdP2O7 and δiso=32.1, δaniso=36.0, η=0.84 for CaPd2(PO4)2.



The First Iridiumphosphates


84Two polymorphs of iridium(III)-metaphosphate Ir(PO3)3 and an iridium(IV)-silicophosphate (Ir1−xSix)3[Si2O(PO4)6] (x ≈ 0.5) were synthesized and their crystal structures determined from single-crystal x-ray data. Pale pink needles of triclinic Ir(PO3)3 (Ru(PO3)3 structure type, P1 (No. 2), Z=2, a=6.9574(6) Å, b=10.3628(9) Å, c=5.0288(4) Å, α=92.28(1)°, β=92.80(1)°, γ=98.60(1)°, 1574 independent reflections, 122 parameters, R1=0.028, wR2=0.061) were grown from a metaphosphoric acid melt. Pale pink prisms of C-type Ir(PO3)3 (C-Al(PO3)3 structure type, Cc (No. 14), Z=12, a=13.103(2) Å, b=19.183(1) Å, c=9.354(1) Å, β=127.19(1)°, 4254 independent reflections, 354 parameter, R1=0.024, wR2=0.062) were obtained by chemical vapour transport (900 °C → 800 °C, addition of IrCl3·xH2O). Both metaphosphates are built of [IrIIIO6] octahedra and infinite 1(PO3-) chains. The latter have a translation period of three phosphate tetrahedra in the triclinic modification and six in the monoclinic. 1D and double-quantum filtered 2D 31P-MAS-NMR spectra of C-type Ir(PO3)3 confirm the chain structure and reveal a chemical shift range between −4,8 and −30,9 ppm for the 9 crystallographically independent, however chemically similar phosphate groups.
Pale orange crystals of (Ir1−xSix)3[Si2O(PO4)6] (Si3[Si2O(PO4)6] structure type, R3 (No. 148), Z=3, a=7.8819(8) Å, c=24.476(4) Å, 1086 independent reflections, 56 parameters, R1=0.061, wR2=0.190) occurred in chemical vapour transport experiments aiming at the crystallization of C-Ir(PO3)3. The crystal structure of the silicophosphate consists of isolated [IrIVO6] octahedra and [Si2O(PO4)6]12− heteropolyanions.



Crystal Structures of Lazulite-Type Oxidephosphates TiIIITiIV3O3(PO4)3 and MIII4TiIV27O24(PO4)24 (MIII = Ti, Cr,Fe)


82sSingle crystals of the oxidephosphates TiIIITiIV3O3(PO4)3 (black), CrIII4TiIV27O24(PO4)24 (red-brown, transparent), and FeIII4TiIV27O24(PO4)24 (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members (space group F2dd ) of the lazulite/lipscombite structure family were refined from single-crystal data [TiIIITiIV3O3(PO4)3: Z=24, a=7.3261(9) Å, b=22.166(5) Å, c=39.239(8) Å, R1=0.029, wR2=0.084, 6055 independent reflections, 301 variables; CrIII4TiIV27O24(PO4)24: Z=1, a=7.419(3) Å, b=21.640(5) Å, c=13.057(4) Å, R1=0.037, wR2=0.097, 1524 independent reflections, 111 variables; FeIII4TiIV27O24(PO4)24: Z=1, a=7.4001(9) Å, b=21.7503(2) Å, c=12.775(3) Å, R1=0.049, wR2=0.140, 1240 independent reflections, 112 variables). For TiIIITiIVO3(PO4)3 a well-ordered structure built from dimers [TiIII,IV2O9] and [TiIV,IV2O9] and phosphate tetrahedra is found. The metal sites in the crystal structures of Cr4Ti27O24(PO4)24 and Fe4Ti27O24(PO4)24, consisting of dimers [MIIITiIVO9] and [TiIV,IV2O9], monomeric [TiIVO6] octahedra, and phosphate tetrahedra, are heavily disordered. Site disorder, leading to partial occupancy of all octahedral voids of the parent lipscombite/lazulite structure, as well as splitting of the metal positions is observed. According to Guinier photographs TiIII4TiIV27O24(PO4)24 (a=7.418(2) Å, b=21.933(6) Å, c=12.948(7) Å) is isotypic to the oxidephosphates MIII4TiIV27O24(PO4)24 (MIII: Cr, Fe). The UV/vis spectrum of Cr4Ti27O24(PO4)24 reveals a rather small ligand-field splitting Δo=14,370 cm−1 and a very low nephelauxetic ratio β=0.72 for the chromophores [CrIIIO6] within the dimers [CrIIITiIVO9].




A New Vanadiumphosphate for Selective Oxidation of Light Alkanes


77A novel vanadium(IV) phosphate VIIIVIV3O3(PO4)3 has been synthesized and crystallized (1073 K, sealed silica tube, a few milligrams of PtCl2 as mineralizer). According to the single-crystal structure analysis [orthorhombic, F2dd (No. 63), Z = 24, a = 7.2596(8) Å, b = 21.786(2) Å, c = 38.904(4) Å (lattice parameters from Guinier photographs), R1 = 0.032, wR2 = 0.067, κ-CCD diffractometer, 83 949 reflections measured, 6836 independent, 5986 with I > 2σ(I), 299 variables], VIIIVIV3O3(PO4)3 belongs to the Lipscombite/Lazulite structure family. At 1073 K VIIIVIV3O3(PO4)3 is in thermodynamic equilibrium with (VO)2P2O7, VO2, and VPO4. Substitution of V3+ in VIIIVIV3O3(PO4)3 by Cr3+ and Fe3+ is possible. Like vanadyl­pyrophosphate the oxide phosphates MIIIVIV3O3(PO4)3 (MIII:  V, Cr, Fe) show significant catalytic activity in selective oxidation of n-butane and 1-butene to maleic acid anhydride.



Second-sphere ligand field effects in solid solutions of

anhydrous transition metal phosphates


73Powders of the solid solutions In1-xCrxPO4 (0 ≤ x ≤ 1), In1-xCrx(PO3)3 (0 ≤ x ≤ 1), (In1-xCrx)4(P2O7)3 (0 ≤ x ≤ 0.7), and In1-xMnx(PO3)3 (0 ≤ x ≤ 0.8) have been synthesized by solid-state reactions. Depending on the dopant concentration, these materials show striking variations in color [In1-xCrxPO4, light pink to green-brown; (In1-xCrx)4(P2O7)3, light pink to red-brown; In1-xCrx(PO3)3, pale green to green; In1-xMnx(PO3)3, light blue to purple). Powder reflectance spectra of the solid solutions were measured in the UV/vis/NIR region (5500−35000 cm-1). Observed d−d electronic transition energies and results of calculations within the framework of the angular overlap model (AOM) for the low-symmetry chromophores [MIIIO6] (M = Cr, Mn) are in good agreement. In the case of the mixed In/Cr phosphates, the observed color changes can be related to second-sphere ligand-field effects. Clear evidence for differences in the π-bonding of oxygen toward Cr3+ (d3 ion) and In3+ (d10 ion) are observed. For In1-xMnx(PO3)3, the variation in color is attributed to a slightly increasing elongation of the [MnIIIO6] chromophore with increasing dopant concentration.



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