Sharon E. Ashbrook

First-Principles Calculation of NMR Parameters Using the Gauge Including Projector Augmented Wave Method: A Chemist’s Point of View

Including Projector Augmented Wave Method: A Chemist’s Point of View Christian Bonhomme,*,† Christel Gervais,*,† Florence Babonneau,† Cristina Coelho,‡ Fred́eŕique Pourpoint,† Thierry Azaïs,† Sharon E. Ashbrook,* John M. Griffin, Jonathan R. Yates,* Francesco Mauri, and Chris J. Pickard †Laboratoire de Chimie de la Matier̀e Condenseé de Paris, Universite ́ Pierre et Marie Curie, Paris 06, CNRS UMR 7574, Colleg̀e de France, 75005 Paris, France ‡IMPC, Institut des Mateŕiaux de Paris Centre, FR2482, UPMC Universite ́ Pierre et Marie Curie Paris 06, Colleg̀e de France, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France School of Chemistry and EaStCHEM, University of St. Andrews, North Haugh, St. Andrews KY16 9ST, United Kingdom Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom Laboratoire de Mineŕalogie Crystallographie, UMR CNRS 7590, Universite ́ Pierre et Marie Curie, UPMC, 75015 Paris, France Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom

A family of zeolites with controlled pore size prepared using a top-down method

The properties of zeolites, and thus their suitability for different applications, are intimately connected with their structures. Synthesizing specific architectures is therefore important, but has remained challenging. Here we report a top-down strategy that involves the disassembly of a parent zeolite, UTL, and its reassembly into two zeolites with targeted topologies, IPC-2 and IPC-4. The three zeolites are closely related as they adopt the same layered structure, and they differ only in how the layers are connected. Choosing different linkers gives rise to different pore sizes, enabling the synthesis of materials with predetermined pore architectures. The structures of the resulting zeolites were characterized by interpreting the X-ray powder-diffraction patterns through models using computational methods; IPC-2 exhibits orthogonal 12- and ten-ring channels, and IPC-4 is a more complex zeolite that comprises orthogonal ten- and eight-ring channels. We describe how this method enables the preparation of functional materials and discuss its potential for targeting other new zeolites.

Early stage reversed crystal growth of zeolite A and its phase transformation to sodalite.

Microstructural analysis of the early stage crystal growth of zeolite A in hydrothermal synthetic conditions revealed a revised crystal growth route from surface to core in the presence of the biopolymer chitosan. The mechanism of this extraordinary crystal growth route is discussed. In the first stage, the precursor and biopolymer aggregated into amorphous spherical particles. Crystallization occurred on the surface of these spheres, forming the typical cubic morphology associated with zeolite A with a very thin crystalline cubic shell and an amorphous core. With a surface-to-core extension of crystallization, sodalite nanoplates were crystallized within the amorphous cores of these zeolite A cubes, most likely due to an increase of pressure. These sodalite nanoplates increased in size, breaking the cubic shells of zeolite A in the process, leading to the phase transformation from zeolite A to sodalite via an Ostwald ripening process. Characterization of specimens was performed using scanning electron microscopy and transmission electron microscopy, supported by other techniques including X-ray diffraction, solid-state NMR, and N(2) adsorption/desorption.

The Polar Phase of NaNbO3: A Combined Study by Powder Diffraction, Solid-State NMR, and First-Principles Calculations

A polar phase of NaNbO(3) has been successfully synthesized using sol-gel techniques. Detailed characterization of this phase has been undertaken using high-resolution powder diffraction (X-ray and neutron) and (23)Na multiple-quantum (MQ) MAS NMR, supported by second harmonic generation measurements and density functional theory calculations. Samples of NaNbO(3) were also synthesized using conventional solid-state methods and were observed to routinely comprise of a mixture of two different polymorphs of NaNbO(3), namely, the well-known orthorhombic phase (space group Pbcm) and the current polar phase, the relative quantities of which vary considerably depending upon precise reaction conditions. Our studies show that each of these two polymorphs of NaNbO(3) contains two crystallographically distinct Na sites. This is consistent with assignment of the polar phase to the orthorhombic space group P2(1)ma, although peak broadenings in the diffraction data suggest a subtle monoclinic distortion. Using carefully monitored molten salt techniques, it was possible to eradicate the polar polymorph and synthesize the pure Pbcm phase.

Multiple-quantum MAS NMR of quadrupolar nuclei. Do five-, seven- and nine-quantum experiments yield higher resolution than the three-quantum experiment?

The question of whether or not higher-order (five-, seven- and nine-quantum) multiple-quantum magic angle spinning (MQMAS) experiments yield isotropic NMR spectra of half-integer quadrupolar nuclei with higher resolution than the basic three-quantum MAS experiment is examined. The frequency dispersion is shown theoretically to be greatly increased in higher-order MQMAS spectra, but it is argued that whether or not this translates into an increase in resolution depends upon the ratio of the homogeneous to inhomogeneous contributions to the isotropic linewidth. Experimentally, it is demonstrated using three-, five- and seven-quantum 45Sc MAS NMR and three- and five-quantum 27Al MAS NMR of crystalline samples that higher-order MQMAS experiments can yield a real and useful increase in resolution but that, owing to the presence of inhomogeneous broadening in the isotropic spectra, this increase is less than the theoretically predicted value. A number of practical issues relating to resolution in MQMAS NMR are also pointed out.

23Na multiple-quantum MAS NMR of the perovskites NaNbO3 and NaTaO3

The distorted perovskites NaTaO3 and NaNbO3 have been studied using 23Na multiple-quantum (MQ) MAS NMR. NaTaO3 was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO3 were studied. The first, a commercially available sample which was annealed at 900 °C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state.

New methods and applications in solid-state NMR spectroscopy of quadrupolar nuclei.

Solid-state nuclear magnetic resonance (NMR) spectroscopy has long been established as offering unique atomic-scale and element-specific insight into the structure, disorder, and dynamics of materials. NMR spectra of quadrupolar nuclei (I > (1)/2) are often perceived as being challenging to acquire and to interpret because of the presence of anisotropic broadening arising from the interaction of the electric field gradient and the nuclear electric quadrupole moment, which broadens the spectral lines, often over several megahertz. Despite the vast amount of information contained in the spectral line shapes, the problems with sensitivity and resolution have, until very recently, limited the application of NMR spectroscopy of quadrupolar nuclei in the solid state. In this Perspective, we provide a brief overview of the quadrupolar interaction, describe some of the basic experimental approaches used for acquiring high-resolution NMR spectra, and discuss the information that these spectra can provide. We then describe some interesting recent examples to showcase some of the more exciting and challenging new applications of NMR spectra of quadrupolar nuclei in the fields of energy materials, microporous materials, Earth sciences, and biomaterials. Finally, we consider the possible directions that this highly informative technique may take in the future.

Motional broadening: an important distinction between multiple-quantum and satellite-transition MAS NMR of quadrupolar nuclei

Abstract Multiple-quantum (MQ) and satellite-transition (ST) magic-angle spinning (MAS) are two very similar techniques used to obtain high-resolution or ‘isotropic’ NMR spectra of half-integer quadrupolar nuclei. In a variety of materials it is observed that some STMAS peaks are very broad compared with the corresponding MQMAS peaks, sometimes so broad that they are unobservable. We present 17 O ( I =5/2) NMR spectra of two materials, chondrodite (2Mg 2 SiO 4 · Mg(OH) 2 ) and clinohumite (4Mg 2 SiO 4 ·Mg(OH) 2 ), exhibiting this phenomenon and show that the cause is motional broadening arising from the combined effects of molecular reorientation, the quadrupolar interaction and MAS.

Multiple-quantum cross-polarization in MAS NMR of quadrupolar nuclei

Abstract Using 27 Al ( I =5/2) NMR of aluminium acetylacetonate, we show that it is possible to cross-polarize from a spin I =1/2 nucleus ( 1 H ) directly to the central triple-quantum transition of a half-integer quadrupolar nucleus ( 27 Al ) in a powdered sample under MAS conditions. The optimum conditions for this multiple-quantum cross-polarization (MQCP) are investigated experimentally and compared with existing theoretical results. The new technique is applied to the recently introduced two-dimensional MQMAS experiment for recording high-resolution NMR spectra of half-integer quadrupolar nuclei.

Task specific ionic liquids for the ionothermal synthesis of siliceous zeolites

The first genuine ionothermal synthesis of siliceous zeolites MFI and TON has been accomplished by utilising the ionic liquid 1-butyl-3-methyl imidazolium bromide/hydroxide as both solvent and structure directing agent.