- Aluminum phosphates with non-centrosymmetric layer- and framework-structures of topologically related motifs: 2. KAl2(PO4)2(OH)·2H2O
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KAl2(PO4)2(OH)·2H2O was obtained by the reaction of gibbsite with a potassium-phosphate solution of pH = 5.5 at 373 K. A single crystal X-ray structure analysis showed that it is an ordered, F-free K-analog of the microporous compound AlPO4-CI2. Crystal data: orthorhombic space group P212121, a = 920.5(1), b = 970.7(2), c = 982.8(2) pm, Z = 4. The structure consists of dimeric units of AlO6 octahedra and AlO5 trigonal bipyramids, bridged by an OH and two bidentate phosphate groups. The dimers are linked by phosphate to form corrugated layers which are topologically related to the layers in KAl2(PO4)2(OH)·2H2O and minyulite. The layers are connected by Al-O-P and hydrogen bonds to a three dimensional framework structure with K ions in channel-like cavities. A neutron powder scattering experiment with KAl2(PO4)2(OD)·2D2O showed that the bridging OD group and only one D of each water molecule are involved in hydrogen bonding. 31P MAS NMR spectra show two isotropic lines at δiso = -6.9 and -18,7 ppm of the intensity ratio 1:1 and confirm the presence of two crystallographically independent P atoms in the unit cell. In the 1H MAS NMR spectra the water molecules and the bridging OH group show signals at 5.9 and 1.1 ppm, respectively.
- Dick, Stefan,Gro?mann, Gisbert,Ohms, Gisela,Mu?ller, Manfred
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- IR spectra of phosphate ions in aqueous solution: Predictions of a DFT/MM approach compared with observations
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Due to the progress of density functional theory (DFT) accurate computations of vibrational spectra of isolated molecules have become a standard task in computational chemistry. This is not yet the case for solution spectra. To contribute to the exploration of corresponding computational procedures, here we suggest a more efficient variant of the so-called instantaneous normal-mode analysis (INMA). This variant applies conventional molecular dynamics (MD) simulations, which are based on nonpolarizable molecular mechanics (MM) force fields, to the rapid generation of a large ensemble of different solvation shells for a solute molecule. Short hybrid simulations, in which the solute is treated by DFT and the aqueous solvent by MM, start from snapshots of the MM solute-solvent MD trajectory and yield a set of statistically independent hydration shells partially adjusted to the DFT/MM force field. Within INMA, these shells are kept fixed at their 300 K structures, line spectra are calculated from the DFT/MM Hessians of the solute, and its inhomogeneously broadened solution spectra are derived by second-order statistics. As our test application we have selected the phosphate ions HPO42- and H2PO4 because sizable solvation effects are expected for the IR spectra of these strongly polarizable ions. The widths, intensities, and spectral positions of the calculated bands are compared with experimental IR spectra recorded by us for the purpose of checking the computational procedures. These comparisons provide insights into the merits and limitations of the available DFT/MM approach to the prediction of IR spectra in the condensed phase.
- Klaehn, Marco,Mathias, Gerald,Koetting, Carsten,Nonella, Marco,Schlitter, Juergen,Gerwert, Klaus,Tavan, Paul
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- Aluminum phosphates with non-centrosymmetric layer- and framework-structures of topologically related motifs: 1. KAl2(PO4)2(OH)·4H2O
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KAl2(PO4)2(OH)·4H2O could be obtained by the reaction of gibbsite with a potassium-phosphate solution of pH = 5.5 at 333 K. A single crystal X-ray structure analysis showed that KAl2(PO4)2(OH)·4H2O is isotypic with the mineral minyulite. Crystal data: orthorhombic space group Pba2, a = 934.7(1), b = 982, 1(1), c = 551, 0(1) pm, Z = 2. It possesses dimeric units of Al-octahedra which are bridged by an OH- and two bidentate phosphate groups. The dimers are linked by phosphate to plane polar layers. Cavities in the layers are occupied by K ions. One corner of each phosphate tetrahedron is not connected to Al but accepts four hydrogen bonds from water molecules bound to Al of the adjacent layer. A powder neutron scattering experiment with KAl2(PO4)2(OD)·4D2O showed that four D atoms and P coordinate the hydrogen bond accepting O in KAl2(PO4)2(OD)·4D2O like a square pyramid. Analogous dimeric building units are found in the Al phosphate minerals minyulite and morinite; similar dimers of Fe octahedra occur in the mineral copiapite, a number of Fe containing enzymes and numerous synthetic iron complexes. High-resolution 31P solid-state NMR spectra show only one isotropic line at δiso = -9.6 ppm and confirm the presence of one symmetry independent phosphorus site in the unit cell. In the 1H-MAS-NMR spectra the water molecules and the bridging OH groups show signals at 5.4 and 1.4 ppm, respectively.
- Dick, Stefan,Gro?mann, Gisbert,Ohms, Gisela,Zeiske, Thomas
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- Phase front and domains during the paraelectric-ferroelectric transition in KD2PO4: Optical observation and dielectric contributions
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Observations of the phase front and the domains during the paraelectric-ferroelectric KD2PO4 phase have been performed in very good thermal homogeneity conditions (thermal gradient equal to 2×10-3 K mm-1). Simultaneously, dielectric and loss constants have also been measured. The phase fronts exhibit a quasiplanar shape perpendicular to the c ferroelectric axis. The ferroelectric region is quasimonodomain when its c dimension is lower than 100 μm. The dielectric constant is demonstrated as the sum of three contributions: a monodomain ε′mono, a contribution of domains ε′d proportional to ε′mono with a coefficient depending on the domain texture, and a contribution due to the existence of the phase front during the phase coexistence.
- Bornarel, Jean,Cach, Ryszard
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- Preparation of alkali-metal dideuterium phosphates
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Methods for the preparation of deuterated orthophosphoric acid and alkali-metal dideuterium phosphates are discussed. The easiest and cheapest way of producing these compounds is via the hydration of massive P2O5 polycrystals obtained by vacuum distillation.
- Lokshin
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p. 720 - 722
(2008/10/08)
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