The reactions of elemental antimony, tellurium, selenium and sulfur as well as antimony telluride and antimony sulfide in melts composed of GaCl3/SbCl3/ACl (A = Cu+, Ag+, PPh4+) yielded Ag(Sb7Te8)[GaCl4](6) (1), (Sb7Se8)[GaCl4](2)[Ga2Cl7](3) (2), (Sb7Se8Cl2)[GaCl4](3) (3) and (Sb7S8Cl2)[GaCl4](3) (4). SbCl3 plays the role of the oxidant, and GaCl3 plays the role of the Lewis acidic chloride ion acceptor. All of the compounds form orange, air-sensitive crystals. The crystal structures consist of discrete, double-cube-shaped, mixed antimony-chalcogen cationic clusters (Sb7Te8)(5+), (Sb7Se8)(5+), (Sb7Se8Cl2)(3+) and (Sb7S8Cl2)(3+). The anions are discrete chloridogallate [GaCl4] and [Ga2Cl7](-) anions. All compounds were characterized by single-crystal X-ray diffraction, energy-dispersive electron beam X-ray fluorescence spectroscopy, Raman vibrational spectroscopy and solid-state Se-77 NMR spectroscopy. Supporting gas-phase and periodic DFT calculations allowed the assignments of the spectra and provided insights into the bonding situation of the hypervalent Sb atoms.

AbstractThe compounds (VI), (VIII), (IX), and (XI), which form orange, air‐sensitive crystals are characterized by single crystal XRD, X‐ray fluorescence spectroscopy, Raman spectroscopy, solid state 77Se NMR spectroscopy, and DFT calculations.

Along the quasi-binary section Li3PO4 - (Cu3PO4)-P-I three different phases (Li3-xCuxPO4)-P-I each with extended homogeneity range occur under equilibrium conditions (650 <= theta ; 700 degrees C). According to single-crystal X-ray structure analyses Phase 1 (0 < x <= 0.7) adopts the HT- or beta-Li3PO4 structure type [(Li2.6Cu0.4PO4)-P-I, Pnma (no. 62), Z = 4, a = 10.4612(2) angstrom, b = 6.1690(3) angstrom, c = 4.9854(2) angstrom, R-1 = 0.023, wR(2) = 0.062, Goof = 1.12] and Phase 2 (0.9 <= x <= 1.8) is isotypic to LT- or alpha-Li3PO4 [(Li2.05Cu0.95PO4)-P-I, Pnm2(1) (no. 31), Z = 2, a = 6.2113(8) angstrom, b = 5.2597(7) angstrom, c = 4.9904(5) angstrom, R-1 = 0.040, wR(2) = 0.108, Goof = 0.98]. A preliminary structure model for the copper-rich Phase 3 (2.1 <= x <= 2.8) [(Li0.6Cu2.4PO4)-P-I, P (3) over bar (no. 147), a = 6.223(1) angstrom, c = 5.3629(5) angstrom] could be refined to R-1 = 0.07. Sharp P-31-MAS-NMR resonances observed in the spectra of (Li2.6Cu0.4PO4)-P-I (delta(iso) = 10.4 ppm), (Li2.05Cu0.95PO4)-P-I (delta(iso) = 12.4 ppm), and (Li0.84Cu2.16PO4)-P-I (delta(iso) = 10.9 ppm) provide evidence for the absence of paramagnetic Cu2+ ions. Pure copper(I) orthophosphate Cu-3(I)(PO4) exists as a homogeneous melt (theta >= 800 degrees C) and can be obtained as thermodynamically metastable solid by quenching. It is isotypic to Phase 3 [a = 6.284(3) angstrom, c = 5.408(5) angstrom]. Electrochemical delithiation of (Li2.05Cu0.95PO4)-P-I (C/10, C/30) indicates two partially reversible oxidation processes between 3.75 V and 4.80 V (vs. Li-0/Li+).

AbstractReVIIO2(PO4) (I) and (ReVII2O5)Si2 [Si2O(PO4)6] (II) are obtained from the reaction of Re2O7 and P4O10 in sealed silica tubes (temperature gradient 400 → 300 °C, 2 d).

(ReO2)-O-VII(PO4) and ((Re2O5)-O-VII)Si-2(o)[(Si2O)-O-t(PO4)(6)] were obtained from Re2O7 and P4O10 in sealed silica tubes (250 ? 400 degrees C). The crystal structures were solved and refined from X-ray single crystal data ((ReO2)-O-VII(PO4): C2/c, Z = 24, a = 14.403(1) angstrom, b = 8.414(1) angstrom, c = 20.647(3) angstrom, = 93.165(8)degrees, T = 123 K, 10352 ind. refl., 218 variables, 24 atoms in asymmetric unit, R-1 = 0.041, wR(2) = 0.106; ((Re2O5)-O-VII)Si-2(o)[(Si2O)-O-t(PO4)(6)]: P http://www.w3.org/1999/xlink, Z = 1, a = 7.8589(3) angstrom, b = 7.8609(3) angstrom, c = 10.8311(4) angstrom, = 85.312(2)degrees, = 73.078(2)degrees, = 60.075(2)degrees, T = 298 K, 2551 ind. reflections, 174 variables, 22 atoms in asymmetric unit, R-1 = 0.078, wR(2) = 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 angstrom d(Re-O) 2.08 angstrom), [(SiO6)-O-IV] octahedra, and [(Si2O)-O-t(PO4)(6)](12-) heteropolyanions. In ReO2(PO4) monomeric perrhenyl ions (ReO2)(3+) (?(O-t,Re, O-t) approximate to 101.5 degrees) are formed. The silicophosphate (Re2O5)Si-2(o)[(Si2O)-O-t(PO4)(6)] contains dinuclear (Re2O5)(4+) cations. P-31-MAS-NMR studies on ReO2(PO4) are in accordance with three independent sites of phosphorus. The results of P-31- and Si-29-MAS-NMR studies on (Re2O5)Si-2(o)[(Si2O)-O-t(PO4)(6)] are in agreement with three crystallographically independent sites for phosphorus and two sites for silicon.

AbstractCrystals of (VO)Ti6(PO4)9 are prepared by solid state reaction of VOPO4 and Ti5O4(PO4)4 in a molar ratio of 3:1 (air, 1023 K, 14 d).

Vanadyl(V)-titanium-orthophosphate ((VO)-O-V)Ti-6(IV)(PO4)(9) is formed by solid state reactions in the temperature range 525 <= 9 <= 780 degrees C. At higher temperature decomposition into V2O5 and the hitherto unknown solid solution Ti(P1-xVx)(2)O-7 (0 <= x <= 0.23; 0.30 <= x <= 0.43) is observed. The process of phase formation has been monitored by MAS-NMR (P-31, V-51) 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 (P6(3)/m (No. 176), Z=2; a=8.4438(3) angstrom, c=22.215(1) angstrom, 14 independent atoms, 87 variables, 2066 unique reflections. R1=0.032, wR2 =0.084) shows the relationship of ((VO)-O-V)Ti-6(IV)(PO4)(9) to the NASICON structure family. In marked contrast to the other members of this family [(Ti2O9)-O-IV] double-octahedra and strongly distorted tetrahedral [(V-V=O)O-3] groups are observed besides isolated [(TiO6)-O-IV] octahedra and phosphate tetrahedra. The structure model is in agreement with the results from MAS-NMR (P-31, V-51) spectroscopy. (C) 2012 Elsevier Inc. All rights reserved.

Attempts to prepare the hitherto unknown Se(6)(2+) cation by the reaction of elemental selenium and Ag[A] ([A](-) = [Sb(OTeF(5))(6)](-), [Al(OC(CF(3))(3))(4)](-)) in SO(2) led to the formation of [(OSO)Ag(Se(6))Ag(OSO)][Sb(OTeF(5))(6)](2)1 and [(OSO)(2)Ag(Se(6))Ag(OSO)(2)][Al(OC(CF(3))(3))(4)](2)2a. 1 could only be prepared by using bromine as co-oxidant, however, bulk 2b (2a with loss of SO(2)) was accessible from Ag[Al(OC(CF(3))(3))(4)] and grey Se in SO(2) (chem. analysis). The reactions of Ag[MF(6)] (M = As, Sb) and elemental selenium led to crystals of 1/∞{[Ag(Se(6))](∞)[Ag(2)(SbF(6))(3)](∞)} 3 and {1/∞[Ag(Se(6))Ag](∞)}[AsF(6)](2)4. Pure bulk 4 was best prepared by the reaction of Se(4)[AsF(6)](2), silver metal and elemental selenium. Attempts to prepare bulk 1 and 3 were unsuccessful. 1-4 were characterized by single-crystal X-ray structure determinations, 2b and 4 additionally by chemical analysis and 4 also by X-ray powder diffraction, FT-Raman and FT-IR spectroscopy. Application of the PRESTO III sequence allowed for the first time (109)Ag MAS NMR investigations of 4 as well as AgF, AgF(2), AgMF(6) and {1/∞[Ag(I(2))](∞)}[MF(6)] (M = As, Sb). Compounds 1 and 2a/b, with the very large counter ions, contain isolated [Ag(Se(6))Ag](2+) heterocubane units consisting of a Se(6) molecule bicapped by two silver cations (local D(3d) sym). 3 and 4, with the smaller anions, contain close packed stacked arrays of Se(6) rings with Ag(+) residing in octahedral holes. Each Ag(+) ion coordinates to three selenium atoms of each adjacent Se(6) ring. 4 contains [Ag(Se(6))(+)](∞) stacks additionally linked by Ag(2)(+) into a two dimensional network. 3 features a remarkable 3-dimensional [Ag(2)(SbF(6))(3)](-) anion held together by strong Sb-FAg contacts between the component Ag(+) and [SbF(6)](-) ions. The hexagonal channels formed by the [Ag(2)(SbF(6))(3)](-) anions are filled by stacks of [Ag(Se(6))(+)](∞) cations. Overall 1-4 are new members of the rare class of metal complexes of neutral main group elemental clusters, in which the main group element is positively polarized due to coordination to a metal ion. Notably, 1 to 4 include the commonly metastable Se(6) molecule as a ligand. The structure, bonding and thermodynamics of 1 to 4 were investigated with the help of quantum chemical calculations (PBE0/TZVPP and (RI-)MP2/TZVPP, in part including COSMO solvation) and Born-Fajans-Haber-cycle calculations. From an analysis of all the available data it appears that the formation of the usually metastable Se(6) molecule from grey selenium is thermodynamically driven by the coordination to the Ag(+) ions.

The reaction of metallic silver with tungsten tetrachlorideoxide WOCl4 or the reaction of AgCl with WOCl3, both at 690 K, lead to Ag1-x[W2O2Cl6] as black lustrous crystal needles. The compound shows a substantial phase field width in the silver content depending on reaction temperature and reaction time and crystals with x = 0, 0.38 and 0.82 were isolated. The crystal structure determinations (monoclinic, C2/m) show the structure to be isotypic to those of Tl[W2O2Cl6] and K-0.84[W2O2Cl6] with the presence of ID polymeric [W2O2Cl6](n) strands and Ag+ ions with a variety in the occupation of the respective crystallographic site. Ag1-x[W2O2Cl6] represents a mixed valence compound with a variable ratio of W(IV) and W(V) in the W-2 dumbbells with a short W-W separation of 2.85 angstrom. In Fourier maps the electron density of the Ag ion appears smeared over a large area. By structure determinations of stoichiometric Ag-1.0[W2O2Cl6] at temperatures of 123, 193, and 293 K a double minimum potential was found with the silver ion dynamically disordered over two flat basins with a thermal activation barrier of 13 meV. No long range ion mobility is present since the Ag+ ions are trapped within a coordinating cage consisting of ten chlorine atoms of the surrounding [W2O2Cl6] strands forming a distorted bicapped cube. By MAS-NMR spectroscopic measurements on the Ag-109 nuclei at different temperatures, the spin lattice relaxation times were determined giving a thermally activated barrier of 15 meV. The electronic conductivity of pressed powder samples of Ag[W2O2Cl6] by a four-probe measurement applying direct current is 1 Omega(-1).cm(-1) at room temperature and 10(-3) Omega(-1).cm(-1) at 25 K. For the conduction mechanism at low temperatures a variable range hopping mechanism is suggested, whereas at higher temperatures a standard semi-conductivity with a bandgap of 60 meV is present.

Title compounds with x = 0, 0.38, and 0.82 are synthesized either by reaction of WOCl3 with AgCl in the presence of a small amount of WCl6 (510700 K, 40 d), or by reaction of WOCl4 with metallic Ag (690 K, 7 d).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Starting from PdO, HgO and P 4 O 10 yellow, plate‐like single crystals of HgPdP 2 O 7 were obtained by chemical vapour transport experiments (600 °C → 500 °C, addition of PdCl 2 ). Micro‐crystalline PbPdP 2 O 7 is synthesized by heating ( T max = 700 °C) stoichiometric amounts of PdO, PbO, and phosphoric acid. Using chemical vapour transport experiments (800 °C → 700 °C, addition of PdCl 2 ) brown plate‐like single crystals of PbPdP 2 O 7 were obtained besides yellow needles of PbPdSi(P 2 O 7 ) 2 . Brown, prismatic crystals of HgPd 2 (PO 4 ) 2 with edge‐lengths up to 1 mm were grown by solvothermal reactions of PdO and HgO with conc. H 3 PO 4 (400 °C, 7d, cooling: 1°/h). The structures of all compounds were determined and refined from X‐ray single crystal data (HgPdP 2 O 7 : C 2/ c , a = 14.117(2) Å, b = 4.884(1) Å, c = 8.802(1) Å, β = 100.9(1)°; PbPdP 2 O 7 : Pnma , a = 13.440(1) Å, b = 5.966(1) Å, c = 7.368(1) Å; PbPdSi(P 2 O 7 ) 2 : P 2 1 / m , a = 4.593(1) Å, b = 17.169(1) Å, c = 6.435(1) Å, β = 101.71(1)°; HgPd 2 (PO 4 ) 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 M Pd 2 (PO 4 ) 2 ( M = Cd, Ca) and M PdP 2 O 7 ( M = Ca, Sr, Ba, Zn) are isotypic to HgPd 2 (PO 4 ) 2 and PbPdP 2 O 7 , respectively. 31 P‐MAS‐NMR studies on HgPdP 2 O 7 and CaPd 2 (PO 4 ) 2 are in accordance with one independent site for phosphorus. Their chemical shifts were determined to δ iso = 24.2 , δ aniso = 83.0 , η = 0.43 for HgPdP 2 O 7 and δ iso = 32.1 , δ aniso = 36.0 , η = 0,84 for CaPd 2 (PO 4 ) 2 .

The normal acid salt isopropylammonium tetrafluorohydrogenphthalate (3) was prepared and its structure was determined by X-ray crystallography. This salt is stabilized by N–H…O, O–H…O, C–H…O, and N–H…F hydrogen bonds. Compound 3 was characterized by means of solution and solid-state NMR. The ipso-carbons, whose signals are equivalent in solution, could be distinguished in the solid state, thus reflecting the asymmetric nature of 3. With respect to structural features, 3 was compared with salts of different stoichiometry, i.e. the neutral salt bis(isopropylammonium) tetrafluorophthalate (1) and the anomalous salt isopropylammonium tetrafluorohydrogenphthalate×tetrafluorophthalic acid (2).

Starting from PdO, HgO and P4O10 Yellow, plate-like single crystals of HgPdP2O7 were obtained by chemical vapour transport experiments (600 degrees C -> 500 degrees C, addition of PdCl2). Micro-crystalline PbPdP2O7 is synthesized by heating (T-max = 700 degrees C) stoichiometric amounts of PdO, PbO, and phosphoric acid. Using chemical vapour transport experiments (800 degrees C -> 700 degrees 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 cone. H3PO4 (400 degrees C, 7d, cooling: 1 degrees/h). The structures of all compounds were determined and refined from X-ray single crystal data (HgPdP2O7: C2/c, a = 14.117(2) angstrom, h = 4.884(1) angstrom , c = 8.802(1) angstrom, beta = 100.9(1)degrees; PbPdP2O7: Pnma, a = 13.440(1) angstrom, b = 5.966(1) angstrom, c = 7.368(1) angstrom; PbPdSi(P2O7)(2): P2(1)/m, a = 4.593(1) angstrom, b = 17.169(1) angstrom, c = 6.435(1) angstrom, beta = 101.71(1)degrees; HgPd2(PO4)(2): Fddd, a = 6.955(1) angstrom, b = 11.342(1) angstrom, c = 15.840(1) degrees). 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. P-31-MAS-NMR studies on HgPdP2O7 and CaPd2(PO4)(2) are in accordance with one independent site for phosphorus. Their chemical shifts were determined to delta(iso) = 24.2, delta(aniso) = 83.0, eta = 0.43 for HgPdP2O7 and delta(iso) = 32.1, delta(aniso) = 36.0, eta = 0,84 for CaPd(PO4)(2).

Structure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO₂ and ZrO₂ synthesized in a microwave-plasma process have been investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and perturbed angular correlation (PAC) spectroscopy. The PAC technique was used to measure the electric quadrupole interactions (QIs) of the nuclear probes ^(181)Ta and ^(111)Cd in nanocrystalline HfO₂ and ZrO₂ as a function of temperature. For comparison, the QI of ^(181)Ta in the bulk oxides was determined in the same temperature range 300 K ≤ T ≤ 1550 K. The oxygen-metal ratio of the as- ynthesized particles was determined by x-ray photoelectron spectroscopy to be in the range 1.4 ≤ x ≤ 1.8. A hydrate surface layer with a hydrogen content of 5–10 wt %, consisting of chemisorbed hydroxyl groups and organic precursor fragments, was detected by ^(1) H magic-angle spinning NMR. XRD and TEM show that bare n-ZrO₂, Al₂O₃-coated n-ZrO₂, and Al₂O₃-coated n-HfO₂ are synthesized in the tetragonal or cubic modification with a particle size d < 5 nm, whereas bare n-HfO₂ is mainly monoclinic. The grain growth activation enthalpy of bare n-ZrO₂ is Q_(A)=32(5)kJ/mol. Coating with Al₂O₃ stabilizes the tetragonal over the monoclinic phase, both in hafnia and zirconia nanoparticles. While TEM micrographs of the native nanoparticles reveal a well-ordered cation sublattice, the observation of a broad QI distribution in the PAC spectra suggests a high degree of disorder of the oxygen sublattice. The gradual transformation of the disordered state and the phase evolution were studied by high-temperature QI measurements. Hafnia nanoparticles persist in the monoclinic (m) phase up to T ≤ 1400 K. In coated n-ZrO₂ /Al₂O₃, the monoclinic and tetragonal (t) phases coexist over a large temperature range, whereas uncoated, initially tetragonal or cubic (t or c) n-ZrO₂ presents a sharp m↔t transition. A “defect” component involving 30%–40% of the probe nuclei appears in the ^(181)Ta PAC spectra of all nanoparticles when these are cooled from high temperatures T ≥ 1200 K. The temperature dependence of this component can be reproduced by assuming that Ta impurities in hafnia and zirconia may trap electrons at low temperatures. The observation that the defect component appears only in nanoparticles with diameter d < 100 nm suggests that mobile electrons are available only in the surface region of the oxide particles, either from oxygen vacancies (Vo) and/or Vo- hydrogen donors at the interface of the nanoparticles and their hydrate layers. This conclusion is supported by the absence of a size effect for ^(111)Cd probes in HfO₂ and ZrO₂. The temperature dependence of the ^(181)Ta defect fraction is consistent with a Ta_(+) impurity level at E_d ~ 0.9 and 0.6 eV below the hafnia and zirconia conduction band, respectively.

Ammonolysis of the monomeric, base-stabilized trisaminoalane Me3N-Al[N(H)Dipp)]3 (Dipp=2,6-iPr2–C6H3) yielded Al–N oligomers, which were characterized in detail by solid state NMR spectroscopy (1H, 13C, 15N, 27Al) and TGA/DTA. Pyrolysis of as-prepared oligomers at different temperatures in an argon steam yielded carbon-containing black solids, whereas pyrolysis under a steady flow of NH3 produced pure aluminum nitride (AlN). The role of the pyrolysis temperature and the influence of NH3 on the formation of crystalline materials were investigated. As-prepared AlN was characterized by solid state NMR spectroscopy (15N, 27Al), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Theoretical calculations were performed in order to identify potential reaction intermediates.

Structure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO2 and ZrO2 synthesized in a microwave-plasma process have been investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and perturbed angular correlation (PAC) spectroscopy. The PAC technique was used to measure the electric quadrupole interactions (QIs) of the nuclear probes Ta-181 and Cd-111 in nanocrystalline HfO2 and ZrO2 as a function of temperature. For comparison, the QI of Ta-181 in the bulk oxides was determined in the same temperature range 300 K <= T <= 1550 K. The oxygen-metal ratio of the as-synthesized particles was determined by x-ray photoelectron spectroscopy to be in the range 1.4 <= x <= 1.8. A hydrate surface layer with a hydrogen content of 5-10 wt %, consisting of chemisorbed hydroxyl groups and organic precursor fragments, was detected by H-1 magic-angle spinning NMR. XRD and TEM show that bare n-ZrO2, Al2O3-coated n-ZrO2, and Al2O3-coated n-HfO2 are synthesized in the tetragonal or cubic modification with a particle size d < 5 nm, whereas bare n-HfO2 is mainly monoclinic. The grain growth activation enthalpy of bare n-ZrO2 is Q(A) = 32(5) kJ/mol. Coating with Al2O3 stabilizes the tetragonal over the monoclinic phase, both in hafnia and zirconia nanoparticles. While TEM micrographs of the native nanoparticles reveal a well-ordered cation sublattice, the observation of a broad QI distribution in the PAC spectra suggests a high degree of disorder of the oxygen sublattice. The gradual transformation of the disordered state and the phase evolution were studied by high-temperature QI measurements. Hafnia nanoparticles persist in the monoclinic (m) phase up to T <= 1400 K. In coated n-ZrO2/Al2O3, the monoclinic and tetragonal (t) phases coexist over a large temperature range, whereas uncoated, initially tetragonal or cubic (t or c) n-ZrO2 presents a sharp m <-> t transition. A "defect" component involving 30%-40% of the probe nuclei appears in the Ta-181 PAC spectra of all nanoparticles when these are cooled from high temperatures T >= 1200 K. The temperature dependence of this component can be reproduced by assuming that Ta impurities in hafnia and zirconia may trap electrons at low temperatures. The observation that the defect component appears only in nanoparticles with diameter d < 100 nm suggests that mobile electrons are available only in the surface region of the oxide particles, either from oxygen vacancies (V-O) and/or V-O-hydrogen donors at the interface of the nanoparticles and their hydrate layers. This conclusion is supported by the absence of a size effect for Cd-111 probes in HfO2 and ZrO2. The temperature dependence of the Ta-181 defect fraction is consistent with a Ta+ impurity level at E-d similar to 0.9 and 0.6 eV below the hafnia and zirconia conduction band, respectively.

An anomalous acid salt (2) in the 2:1 ratio of tetrafluorophthalic acid and isopropylamine was prepared from bis(isopropylammonium) tetrafluorophthalate (1). Both salts were characterized by 13C NMR spectroscopy in solution and in solid state, as well as X-ray crystallography. Crystallographic data revealed that molecules of 2 contain a tetrafluorophthalic acid component and a tetrafluorohydrogenphthalate unit. The geometrical arrangement in the crystal structure of 2 can be attributed to a network of intermolecular N–H···O, O–H···O, and C–H···O hydrogen bonds. Fluorine atoms were not involved in such interactions. The 13C NMR chemical shifts of solutions 1 and 2, as well as tetrafluorophthalic acid are discussed. In case of the salt 2, only four different signals were observed for the aromatic and CO carbons and thus, all carboxyl/carboxylate groups appear to be equivalent in solution. In the solid-state NMR spectrum of 2, a splitting into three resonances arising from the ipso-carbons was observed, in agreement with the anomalous acid salt structure.

Structure, phase transformations, grain growth, and defects of bare and alumina-coated nanoparticles of HfO₂ and ZrO₂ synthesized in a microwave-plasma process have been investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and perturbed angular correlation (PAC) spectroscopy. The PAC technique was used to measure the electric quadrupole interactions (QIs) of the nuclear probes ^(181)Ta and ^(111)Cd in nanocrystalline HfO₂ and ZrO₂ as a function of temperature. For comparison, the QI of ^(181)Ta in the bulk oxides was determined in the same temperature range 300 K ≤ T ≤ 1550 K. The oxygen-metal ratio of the as- ynthesized particles was determined by x-ray photoelectron spectroscopy to be in the range 1.4 ≤ x ≤ 1.8. A hydrate surface layer with a hydrogen content of 5–10 wt %, consisting of chemisorbed hydroxyl groups and organic precursor fragments, was detected by ^(1) H magic-angle spinning NMR. XRD and TEM show that bare n-ZrO₂, Al₂O₃-coated n-ZrO₂, and Al₂O₃-coated n-HfO₂ are synthesized in the tetragonal or cubic modification with a particle size d < 5 nm, whereas bare n-HfO₂ is mainly monoclinic. The grain growth activation enthalpy of bare n-ZrO₂ is Q_(A)=32(5)kJ/mol. Coating with Al₂O₃ stabilizes the tetragonal over the monoclinic phase, both in hafnia and zirconia nanoparticles. While TEM micrographs of the native nanoparticles reveal a well-ordered cation sublattice, the observation of a broad QI distribution in the PAC spectra suggests a high degree of disorder of the oxygen sublattice. The gradual transformation of the disordered state and the phase evolution were studied by high-temperature QI measurements. Hafnia nanoparticles persist in the monoclinic (m) phase up to T ≤ 1400 K. In coated n-ZrO₂ /Al₂O₃, the monoclinic and tetragonal (t) phases coexist over a large temperature range, whereas uncoated, initially tetragonal or cubic (t or c) n-ZrO₂ presents a sharp m↔t transition. A “defect” component involving 30%–40% of the probe nuclei appears in the ^(181)Ta PAC spectra of all nanoparticles when these are cooled from high temperatures T ≥ 1200 K. The temperature dependence of this component can be reproduced by assuming that Ta impurities in hafnia and zirconia may trap electrons at low temperatures. The observation that the defect component appears only in nanoparticles with diameter d < 100 nm suggests that mobile electrons are available only in the surface region of the oxide particles, either from oxygen vacancies (Vo) and/or Vo- hydrogen donors at the interface of the nanoparticles and their hydrate layers. This conclusion is supported by the absence of a size effect for ^(111)Cd probes in HfO₂ and ZrO₂. The temperature dependence of the ^(181)Ta defect fraction is consistent with a Ta_(+) impurity level at E_d ~ 0.9 and 0.6 eV below the hafnia and zirconia conduction band, respectively.