Die Kristallstruktur von Si5O[PO4]6

Ionic Dissociation of SiCl4 : Formation of [SiL6 ]Cl4 with L=Dimethylphosphinic Acid

Reactions of SiCl₄ with R₂PO(OH) (R=Me, Cl) yield compounds with six‐fold coordinated silicon atoms. Whereas R=Me afforded the hexacoordinated tetra‐cationic silicon complex [Si(Me₂PO(OH))₆]⁴⁺ with chloride counter‐ions, R=Cl caused release of HCl with formation of a cyclic dimeric silicon complex [Si(Cl₂PO(OH))(Cl₂PO₂)₃(μ‐Cl₂PO₂)]₂ with bridging bidentate dichlorophosphates.

31P MAS NMR and DFT study of crystalline phosphate matrices

We present the study of the phosphorus local environment by using ³¹P MAS NMR in a series of seven double monophosphates M^IIM^IV(PO₄)₂ (M^II and M^IV being divalent and tetravalent cations, respectively) of yavapaiite and low-yavapaiite type crystal structures. Solid-state and cluster DFT calculations were found to be efficient for predicting the ³¹P isotropic chemical shift and chemical shift anisotropy. To achieve this performance, however, a proper computational optimisation of the experimental structural data was required. From the three optimisation methods tested, the full optimisation provided the best reference structure for the calculation of the NMR parameters of the studied phosphates. Also, a better prediction of the chemical shifts was possible by using a correction to the GIPAW calculated shielding.

Five- and six-fold coordinated silicon in silicodiphosphonates: short range order investigation by solid-state NMR spectroscopy

Silicodiphosphonates synthesized by two different pathways show interesting chemical shifts of five- and sixfold coordinated silicon.

Investigation of the effects of phosphorus on the selective hydrodeoxygenation of anisole over an Fe/SiO2 catalyst

Hydrodeoxygenation (HDO) of lignin derivatives offers an effective approach to produce aromatics.

A linear bridging angle in the pyrovanadate group within the crystal structure of Hg₂V₂Te₂O₁₁

The title compound, dimercury(II) divanadium(V) ditellurium(IV) undecaoxide, Hg2V2Te2O11, is a new representative within the family of divalent oxovanadato(V)tellurates(IV). The anionic framework is made up of disphenoidal [TeO4] polyhedra that are linked by corner-sharing to two neighbouring pyrovanadate units, resulting in chains of six-membered rings propagating parallel to [1-10]. The bridging O atom of the pyrovanadate unit is located on an inversion centre, leading to a staggered conformation and a linear V-O-V angle between the two [VO4] tetrahedra. The anionic chains are connected by interjacent six-coordinate Hg(2+) cations into a three-dimensional framework. The 5s(2) lone electron pair of the Te(IV) atom is stereochemically active and protrudes into the free space of the chain links.

Non-aqueous template-assisted synthesis of mesoporous nanocrystalline silicon orthophosphate

Mesoporous nanocrystalline silicon orthophosphate Si₅P₆O₂₅ was synthesized by the non-hydrolytic sol–gel reaction in the presence of Pluronic P123 template and displays superior catalytic activity and selectivity in methylstyrene dimerization.

New perspectives in the PAW/GIPAW approach: J(P-O-Si) coupling constants, antisymmetric parts of shift tensors and NQR predictions

In 2001, Pickard and Mauri implemented the gauge including projected augmented wave (GIPAW) protocol for first-principles calculations of NMR parameters using periodic boundary conditions (chemical shift anisotropy and electric field gradient tensors). In this paper, three potentially interesting perspectives in connection with PAW/GIPAW in solid-state NMR and pure nuclear quadrupole resonance (NQR) are presented: (i) the calculation of J coupling tensors in inorganic solids; (ii) the calculation of the antisymmetric part of chemical shift tensors and (iii) the prediction of (14)N and (35)Cl pure NQR resonances including dynamics. We believe that these topics should open new insights in the combination of GIPAW, NMR/NQR crystallography, temperature effects and dynamics. Points (i), (ii) and (iii) will be illustrated by selected examples: (i) chemical shift tensors and heteronuclear (2)J(P-O-Si) coupling constants in the case of silicophosphates and calcium phosphates [Si(5)O(PO(4))(6), SiP(2)O(7) polymorphs and α-Ca(PO(3))(2)]; (ii) antisymmetric chemical shift tensors in cyclopropene derivatives, C(3)X(4) (X = H, Cl, F) and (iii) (14)N and (35)Cl NQR predictions in the case of RDX (C(3)H(6)N(6)O(6)), β-HMX (C(4)H(8)N(8)O(8)), α-NTO (C(2)H(2)N(4)O(3)) and AlOPCl(6). RDX, β-HMX and α-NTO are explosive compounds.

Efficiency of the Refocused31P−29Si MAS-J-INEPT NMR Experiment for the Characterization of Silicophosphate Crystalline Phases and Amorphous Gels

One- and two-dimensional refocused MAS-J-INEPT NMR experiments in the solid state (through-bond polarization transfer) involving the highly abundant 31P spin and the rare 29Si spin are described for the crystalline silicophosphate phase Si5O(PO4)6 and complex mixtures of SiP2O7 polymorphs. The evaluation of the 2JP-O-Si coupling constants for all 29Si sites is obtained by the careful analysis of the INEPT build-up curves under fast MAS. The results are in agreement with the crystallographic data, taking into account the various J coupling paths. The efficiency of the experiment is demonstrated by its application to more complex systems such as silicophosphate amorphous gels (obtained by the sol-gel process).

Application of the MAS-J-HMQC experiment to a new pair of nuclei {29Si,31P}: Si5O(PO4)6 and SiP2O7 polymorphs

We report the results of the two-dimensional MAS-J-HMQC experiment providing scalar correlations between 29Si and 31P nuclei in solid state NMR, and we give the first evaluation of the 2JSi-O-P coupling constants (approximately 15 Hz) for a crystalline silicophosphate phase Si5O(PO4)6. The experiment is applied to the characterization of complex mixtures of SiP2O7 phases, through editing of 31P spin pairs by the heteronuclear 2JP-O-Si interaction.

Studies of silicophosphate derivatives by 31P-->29Si CP MAS NMR

We show that it is possible to efficiently transfer magnetization from 31P to 29Si, using variable amplitude CP MAS experiment. This experiment is demonstrated by using Si5O(PO4)6, the synthesis protocol of which is described. From the obtained results, we show that the experiment allows the spectral edition of 29Si spectra from 31P-->29Si CP, enabling the studies of derivatives involving Si-O-P linkages, such as phosphosilicate glasses, microporous silicoaluminophosphates (SAPO) and bioactive phosphosilicates.

Local Structure and Chemical Shifts for Six-Coordinated Silicon in High-Pressure Mantle Phases

Most of the earth's mantle is made up of high-pressure silicate minerals that contain octahedrally coordinated silicon (Si(VI)), but many thermodynamically important details of cation site ordering remain unknown. Silicon-29 nuclear magnetic resonance (NMR) spectroscopy is potentially very useful for determining short-range structure. A systematic study of silicon-29 chemical shifts for Si(VI) has revealed empirical correlations between shift and structure that are useful in understanding several new calcium silicates. The observed ordering state of a number of high-pressure magnesium silicates is consistent with the results of previous x-ray diffraction studies.