The room-temperature superstructure of ZrP2O7 is orthorhombic: there are no unusual 180 degrees P-O-P bond angles

The structure of room-temperature ZrP2O7 is shown to be orthorhombic by a combination of high-resolution synchrotron powder diffraction and single-crystal synchrotron diffraction data. Small nontwinned single crystals were obtained by synthesizing the compound using solvothermal methods at temperatures below the cubic to orthorhombic phase transition. The average P-O-P angle is 146 degrees. DFT calculations (B3LYP/AUG-cc-pVDZ) on the isolated P2O7(4-) anion yield a P-O-P angle of 153.42 degrees and indicate that the barrier to inversion is of the order 3.6 kJ mol(-1).     

The 136-atom structure of ZrP2O7 and HfP2O7 from powder diffraction data

There has been considerable debate in the literature about the true room-temperature structure of ZrP2O7 and related materials. In this article we describe how a combination of information from solid-state 31P NMR and powder diffraction data can be used to determine the structure of this 136 unique-atom material. The structure has been solved using a combination of simulated annealing and Rietveld refinement performed simultaneously on X-ray and neutron diffraction data. Despite the close to cubic metric symmetry of the material, we show how its true orthorhombic structure (space group Pbca) can be refined to a high degree of precision.     

A perfectly hydrophobic surface (thetaA/thetaR = 180 degrees /180 degrees)

A perfectly hydrophobic surface with both advancing and receding water contact angles of 180 degrees was prepared using a facile method on a silicon wafer. Phase separation of a toluene-swollen covalently attached methylsilicone results in a nanoscale network structure that is responsible for the superhydrophobicity. A method for testing extreme hydrophobicity was devised to distinguish between surfaces exhibiting contact angles of 180 and 179 degrees .     

Structural environment of uranium (VI) species sorbed onto ZrP2O7: X-ray absorption spectroscopy study

The structure of the surface complex formed during the sorption of UO₂²⁺_aq ion onto the selected phosphate solid has been investigated mainly using X-ray absorption spectroscopy. Samples were prepared by batch experiments. L_III U edge measurements have shown that uranyl ions are sorbed on the phosphate surface as a mononuclear bidentate inner-sphere complex.     

A commercially available perfectly hydrophobic material (thetaA/thetaR = 180 degrees/180 degrees)

We report contact angle studies of compressed samples of a commercially available lubricant (variable diameter submicrometer particles of tetrafluoroethylene oligomers) that indicate that this surface is perfectly hydrophobic (thetaA/thetaR = 180 degrees/180 degrees). We also report X-ray photoelectron spectroscopy (XPS) spectra, a scanning electron microscopy (SEM) micrograph, and 19F NMR characterization data, as it is a material for which no characterization data are available. These samples exhibit the most general lyophobicity of any material reported, showing nearly 180 degrees contact angles with other liquids. That this material is commercially available (in kilogram quantities) will allow other groups, particularly nonsynthetic ones, to prepare and study perfectly hydrophobic surfaces. It should also have an impact on education: demonstration of superhydrophobicity in classrooms is trivial to do with this material.     

The effect of temperature on the sorption of U(VI) onto ZrP2O7 in the presence of oxalic acid

The sorption of uranium onto ZrP₂O₇ in the presence of oxalic acid has been investigated as a function of temperature (20, 40 and 60 °C). Using several complementary analytical methods to characterize the solid surface, it has been shown that the oxalic acid interact with the zirconium diphosphate affecting its surface reactivity. A significant influence of temperature on the sorption reaction has been revealed in the batch experiments. Temperature dependence sorption data and microcalorimetric measurements have been used to determine enthalpy change associated to the sorption reaction. The results have shown that oxalic acid has an important effect on uranium sorption, which is more evident at 60 °C.     

NaMn6(P2O7)2(P3O10) and KCd6(P2O7)2(P3O10)

The crystal structures of two new diphosphates, sodium hexamanganese bis­(diphosphate) triphosphate, NaMn₆(P₂O₇)₂(P₃O₁₀), and potassium hexacadmium bis­(diphosphate) triphosphate, KCd₆(P₂O₇)₂(P₃O₁₀), confirm the rigidity of the M₆(P₂O₇)₂(P₃O₁₀) matrix (M is Mn or Cd) and the relatively fixed dimensions of the tunnels extending in the a direction of the unit cell. The compounds are isomorphous; the P₂O₇^4? anion and the alkali metal cations lie on mirror planes. Bond‐valence analysis of the bonding details of the atoms found within the tunnels permits a prediction of the conductivity.     

Fe2P2O7(H2O)2

The compound diiron diphosphate dihydrate, Fe₂P₂O₇(H₂O)₂, was synthesized hydro­thermally and crystallizes in the monoclinic space group P2₁/n. The compound has a somewhat open framework made up of edge‐sharing iron(II) octahedra that form chains connected by five bridging diphosphates. The remaining octahedral site of each iron is occupied by coordinated water. The H atoms of the water molecules all point into a common channel.     

Ionic Conduction in In3+‐doped ZrP2O7 at Intermediate Temperatures

A new series of Zr_1?xIn_xP₂O₇ (x=0.03, 0.06, 0.09, 0.12) samples were prepared by a solid state reaction method. XRD patterns indicated that the samples of x=0.03–0.09 exhibited a single cubic phase structure, and the doping limit of In³⁺ in ZrP₂O₇ was x=0.09. The conduction behavior was investigated in wet hydrogen using various electrochemical methods including AC impedance spectroscopy, isotope effect, gas concentration cells at intermediate temperatures (373–573 K). The conductivities were affected by the doping levels, and increased in the order: σ (x=0.03)<σ (x=0.12)<σ (x=0.06)<σ (x=0.09). The highest conductivity was observed for the sample Zr_0.91In_0.09P₂O₇ to be 1.59×10^?2 S·cm^?1 in wet hydrogen at 573 K. The isotope effect also confirmed the proton conduction of the sample under water vapor‐containing atmosphere. It was found that in wet hydrogen atmosphere Zr_0.91In_0.09P₂O₇ was almost pure ionic conductor, the ionic conduction was contributed mainly to proton and partially to oxide ionic. The H₂/air fuel cell using x=0.09 sample as electrolyte (thickness: 1.73 mm) generated a maximum power density of 13.5 mW·cm^?2 at 423 K and 16.9 mW·cm^?2 at 448 K, respectively.     

KZn(HP2O7)·2H2O and KMn(HP2O7)·2H2O: acid pyrophosphate metallates(II) with layer structures

The crystal structures of the isomorphous title compounds, namely potassium zinc hydrogen pyrophosphate dihydrate and potassium manganese hydrogen pyrophosphate dihydrate, consist of acidic pyrophosphate–metallate(II) layers joined by K⁺ ions and hydrogen‐bridging bonds. The Zn²⁺/Mn²⁺ ions are octahedrally surrounded by four pyrophosphate O atoms and by two water mol­ecules. The (HP₂O₇)^3? anions exhibit eclipsed conformations. The metal ions and water O atoms lie on mirror planes, as does the central O atom of the (HP₂O₇)^3? anion.     

A space group assignment of ZrP2O7 obtained by 31P solid state NMR

2-D 31P dipolar recoupling magic angle spinning NMR has been used to determine the true symmetry of the low temperature structure of ZrP2O7 for the first time.     

Vapor Phase Vibrational Spectra for Re(2)O(7) and the Infrared Spectrum of Gaseous HReO(4). Molecular Shapes of Mn(2)O(7), Tc(2)O(7), and Re(2)O(7)

The Raman and infrared spectra of gas phase Re(2)O(7) are reported. The experimental vibrational spectra of molecular Tc(2)O(7) and Re(2)O(7) are compared with calculated spectra. The results of these studies agree with a nonlinear M-O-M bridge for Tc(2)O(7) and Re(2)O(7). For infrared intensity calculations, the point charge approximation is used, while for the Raman calculations a combination of bond and atom polarizabilities is adopted. Pure Re(2)O(7) was prepared from rhenium wire, but attempts to prepare it from rhenium powder and oxygen always led to infrared spectra showing serious contamination from a species containing an -OH linkage. Detailed experiments identified this molecule as HReO(4), a unique transition metal analogue of the perhalic acids, and a partial infrared spectrum of this molecule is reported.     

Bond Angles in Lactones and Lactams

The carbonyl group in lactones and, to a lesser extent, in lactams tends to show a C? C?O angle that is larger than the O? C?O or N? C?O angle, the difference increasing in magnitude as the ring size decreases. The observed trend provides information on ratios of force constants characterising the flexibility of the s-cis-ester group and may be interpreted in terms of incipient chemical reaction to ^?O? (CH₂)_n? C?O⁺. Molecular orbital calculations (MINDO/3, MNDO, EH) for model compounds provide an electronic interpretation of this angle difference in terms of an anomeric interaction between the p-type lone pair on the carbonyl O-atom and the antibonding C-O or C-N orbital.     

Kristallstrukturen des Sr(BrO3)2 · H2O,Ba(BrO3)2 · H2O,Ba(IO3)2 · H2O,Pb(CIO3)2 · H2O und Pb(BrO3)2 · H2O

Crystal Structure of Sr(BrO₃)₂ · H₂O, Ba(BrO₃)₂ · H₂O, Ba(IO₃)₂ · H₂O, Pb(ClO₃)₂ · H₂O, and Pb(BrO₃)₂ · H₂O The crystall structures of the isostructural halates Sr(BrO₃)₂ · H₂O, Ba(BrO₃)₂ · H₂O, Ba(IO₃)₂ · H₂O, Pb(ClO₃)₂ · H₂O, and Pb(BrO₃)₂ · H₂O were determined using X-ray single crystal data (monoclinic space group C2/c? C, Z = 4), The mean bond lengths and bond angles of the halate ions in the Ba(ClO₃)₂ · 1 H₂O-type compounds, which correspond to those of other halates, are Cl? O, 149.0, Br? O, 165.9, I? O, 180.2 pm, ClO₃^?, 106.4, BrO₃^?, 104.0, and IO₃^?, 99.6°. The structure data obtained are discussed in terms of possible orientational disorder of the water molecules, strengths of the hydrogen bonds, influence of the lead ions on the structure, and site group distortion of the halate ions.     

Effect of pH, fulvic acid and temperature on the sorption of uranyl on ZrP2O7

The sorption of UO ₂ ²⁺ onto ZrP₂O₇ was studied using the batch technique and the point of zero charge of ZrP₂O₇ was obtained through mass titration. The results indicated that sorption of UO ₂ ²⁺ onto ZrP₂O₇ was strongly affected by pH, solid-to-liquid ratio (m/V), the species of electrolyte in solution and fulvic acid (FA), but was insensitive to ionic strength. The sorption of UO ₂ ²⁺ increased with increasing pH and m/V. The presence of FA enhanced UO ₂ ²⁺ sorption onto ZrP₂O₇ at low pH. The presence of phosphate or sulfate caused opposite effects on the sorption of UO ₂ ²⁺ onto ZrP₂O₇. Addition of citrate also significantly affected UO ₂ ²⁺ sorption. The sorption of UO ₂ ²⁺ increased as the temperature of the system increased. The Langmuir and Freundlich models were used to simulate the sorption isotherms of UO ₂ ²⁺ onto ZrP₂O₇ at different temperatures. The results indicated that the Freundlich model described UO ₂ ²⁺ sorption better than the Langmuir model. Thermodynamic parameters for the sorption process were calculated from the temperature dependent sorption isotherms. The results suggested that the sorption process of UO ₂ ²⁺ onto ZrP₂O₇ is spontaneous and endothermic. The desorption process of UO ₂ ²⁺ from ZrP₂O₇ was also investigated and it was found that sorption onto ZrP₂O₇ was irreversible.