Investigation of Bistetramethylammonium Hydrogencyclotriphosphate-A Molecular Rotor?

The crystalline phase ß-[N(CH3 )4 ]2 HP3 O9 undergoes a reversible phase transition to γ-[N(CH3 )4 ]2 HP3 O9 , which was studied by dynamic scanning calorimetry and X-ray diffraction. The rotational dynamics of the anion [P3 O9 ]3- were evident from variable temperature 31 P magic angle spinning (MAS) NMR spectroscopy. The rotational dynamics could be simulated with a 3-site jump model, which yields spectra in good agreement with experiment. An activation energy of 0.6 eV could be estimated from line shape analysis. Impedance spectra reflect a bulk proton conductivity of γ-[N(CH3 )4 ]2 HP3 O9 of 6.9×10-5  S cm-1 at 240 °C and an activation energy of approximately 1.0 eV. Thus this salt features bulk protonic motion, while local rotational anionic motion happens with activation energies of the same order, as suggested by the paddle-wheel mechanism.

Linking 31P magnetic shielding tensors to crystal structures: experimental and theoretical studies on metal(II) aminotris(methylenephosphonates).

The (31)P chemical shift tensor of the phosphonate group [RC-PO(2)(OH)](-) is investigated with respect to its principal axis values and its orientation in a local coordinate system (LCS) defined from the P atom and the directly coordinated atoms. For this purpose, six crystalline metal aminotris(methylenephosphonates), MAMP·xH(2)O with M = Zn, Mg, Ca, Sr, Ba, and (2Na) and x = 3, 3, 4.5, 0, 0, and 1.5, respectively, were synthesized and identified by diffraction methods. The crystal structure of water-free BaAMP is described here for the first time. The principal components of the (31)P shift tensor were determined from powders by magic-angle-spinning NMR. Peak assignments and orientations of the chemical shift tensors were established by quantum-chemical calculations from first principles using the extended embedded ion method. Structure optimizations of the H-atom positions were necessary to obtain the chemical shift tensors reliably. We show that the (31)P tensor orientation can be predicted within certain error limits from a well-chosen LCS, which reflects the pseudosymmetry of the phosphonate environment.

Occurrence of difluorine F2 in nature--in†situ proof and quantification by NMR spectroscopy.

The most reactive chemical element, F(2), has been claimed not to occur in nature. First direct evidence from in situ NMR spectroscopy now proves that elemental F(2) indeed occurs in nature as an occlusion in "antozonite" (right in the picture), a variant of fluorite (CaF(2), left).

Synthesis and characterization of methylammonium phosphates as crystalline approximants for anhydrous, low melting phosphate glasses.

Low-melting methylammonium phosphate glasses are synthesized from crystalline starting agents. To this end crystalline tris(methylammonium) cyclotriphosphate [CH3NH3]3P3O9, was synthesized by a novel and simple synthesis route from P4O10 and N-methylformamide. It, undergoes an irreversible phase transition to methylammonium catena-polyphosphate [CH3NH3]PO3. The crystal structure of the catena-polyphosphate was solved and refined from X-ray powder diffraction data by the Rietveld method using constraints obtained by solid-state 31P and 1H NMR spectroscopy. This compound crystallizes in a triclinic space group with a = 13.2236(9), b = 7.8924(6), c = 4.6553(2) Å, α = 91.068(4), ß = 87.840(5) and γ = 106.550(3)°. Quantum chemical calculations confirm that the obtained structure lies at an energetic minimum. Finally the reaction of tris(methylammonium) cyclotriphosphate and P4O10 into methylammonium phosphate glass is presented. The synthesized, water-free phosphate glass shows a very low glass transition temperature T g of 33 °C, which was verified by dynamic scanning calorimetry and NMR. The chain-like crystal structure of the high-temperature methylammoniumphosphate [CH3NH3]PO3 serves as an approximation for the short-range order of the glass.

Low temperature synthesis of ionic phosphates in dimethyl sulfoxide.

A new synthesis route for phosphates in an organic solvent at low temperatures is presented. The synthesis was done by dispersing a nitrate salt and phosphorus pentoxide in dimethyl sulfoxide. The synthesis can be performed under water-free conditions and yielded several organic and inorganic phosphates. Crystal structure solution of bistetramethylammonium hydrogencyclotriphosphate, [N(CH3)4]2HP3O9, was achieved by combining information gained from powder X-ray diffraction, liquid NMR and solid state (2D) NMR. The molecular structure of rubidium cyclotetraphosphate, Rb4P4O12, was determined using liquid state NMR and solid state (2D) NMR spectroscopy.