Editorial

An introduction to this re-launch edition of the journal by the new members of the editorial tea

Calculating NMR parameters in aluminophosphates : evaluation of dispersion correction schemes

Periodic density functional theory (DFT) calculations have recently emerged as a popular tool for assigning solid-state nuclear magnetic resonance (NMR) spectra. However, in order for the calculations to yield accurate results, accurate structural models are also required. In many cases the structural model (often derived from crystallographic diffraction) must be optimised (i.e., to an energy minimum) using DFT prior to the calculation of NMR parameters. However, DFT does not reproduce weak long-range "dispersion'' interactions well, and optimisation using some functionals can expand the crystallographic unit cell, particularly when dispersion interactions are important in defining the structure. Recently, dispersion-corrected DFT (DFT-D) has been extended to periodic calculations, to compensate for these missing interactions. Here, we investigate whether dispersion corrections are important for aluminophosphate zeolites (AlPOs) by comparing the structures optimised by DFT and DFT-D (using the PBE functional). For as-made AlPOs (containing cationic structure-directing agents (SDAs) and framework-bound anions) dispersion interactions appear to be important, with significant changes between the DFT and DFT-D unit cells. However, for calcined AlPOs, where the SDA-anion pairs are removed, dispersion interactions appear much less important, and the DFT and DFT-D unit cells are similar. We show that, while the different optimisation strategies yield similar calculated NMR parameters (providing that the atomic positions are optimised), the DFT-D optimisations provide structures in better agreement with the experimental diffraction measurements. Therefore, it appears that DFT-D calculations can, and should, be used for the optimisation of calcined and as-made AlPOs, in order to provide the closest agreement with all experimental measurements.PostprintPeer reviewe

Characterisation of inorganic materials using solid-state NMR spectroscopy

This thesis uses solid-state nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations to study local structure and disorder in inorganic materials. Initial work concerns microporous aluminophosphate frameworks, where the importance of semi-empirical dispersion correction (SEDC) schemes in structural optimisation using DFT is evaluated. These schemes provide structures in better agreement with experimental diffraction measurements, but very similar NMR parameters are obtained for any structures where the atomic coordinates are optimised, owing to the similarity of the local geometry. The ³¹P anisotropic shielding parameters (Ω and κ) are then measured using amplified PASS experiments, but there appears to be no strong correlation of these with any single geometrical parameter. In subsequent work, a range of zeolitic imidazolate frameworks (ZIFs) are investigated. Assignment of ¹³C and ¹⁵N NMR spectra, and measurement of the anisotropic NMR parameters, enabled the number and type of linkers present to be determined. For ¹⁵N, differences in Ω may provide information on the framework topology. While ⁶⁷Zn measurements are experimentally challenging and periodic DFT calculations are currently unreliable, calculations on small model clusters provide good agreement with experiment and indicate that ⁶⁷Zn NMR spectra are sensitive to the local structure. Finally, a series of pyrochlore-based ceramics (Y₂Hf₂₋ₓSnₓO₇) is investigated. A phase transformation from pyrochlore to a disordered defect fluorite phase is predicted, but ⁸⁹Y and ¹¹⁹Sn NMR reveal that rather than a solid solution, a significant two-phase region is present, with a maximum of ~12% Hf incorporated into the pyrochlore phase. The use of ¹⁷O NMR to provide insight into the local structure and disorder in these materials is also investigated. Once the different T₁ relaxation and nutation behaviour is considered it is shown that quantitative ¹⁷O enrichment of Y₂Sn₂O₇ is possible, and that ¹⁷O does offer a promising future tool for study

Investigation of zeolitic imidazolate frameworks using 13C and 15N solid-state NMR spectroscopy

The authors are grateful to EPSRC computational support through the Collaborative Computational Project on NMR Crystallography (CCP-NC), via EP/M022501/1, and for other support through EP/G062129/1 (JK) and EP/M506631/1 (SS). AFO acknowledges funding from the European Community Seventh Framework Program (FP7/2007-2013 [grant agreement number 608490], Project M4CO2). SEA would also like to thank the Royal Society and Wolfson Foundation for a merit award. AFO would also like to acknowledge the SCI for a scholarship for her PhD studies. Some of the calculations were performed on the ARCHER UK National Supercomputing Service, and were supported by CCP-NC. The research data (and/or materials) supporting this publication can be accessed at http://dx.doi.org/10.17630/7959a81e-161d-4ada-9914-08d3d235ce88Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal-organic frameworks (MOFs) with extended three-dimensional networks of transition metal nodes (bridged by rigid imidazolate linkers), with potential applications in gas storage and separation, sensing and controlled delivery of drug molecules. Here, we investigate the use of 13C and 15N solid-state NMR spectroscopy to characterise the local structure and disorder in a variety of single- and dual-linker ZIFs. In most cases, a combination of a basic knowledge of chemical shifts typically observed in solution-state NMR spectroscopy and the use of dipolar dephasing NMR experiments to reveal information about quaternary carbon species are combined to enable spectral assignment. Accurate measurement of the anisotropic components of the chemical shift provided additional information to characterise the local environment and the possibility of trying to understand the relationships between NMR parameters and both local and long-range structure. First-principles calculations on some of the simpler, ordered ZIFs were possible, and provided support for the spectral assignments, while comparison of these model systems to more disordered ZIFs aided interpretation of the more complex spectra obtained. It is shown that 13C and 15N NMR are sufficiently sensitive to detect small changes in the local environment, e.g., functionalisation of the linker, crystallographic inequivalence and changes to the framework topology, while the relative proportion of each linker present can be obtained by comparing relative intensities of resonances corresponding to chemically-similar species in cross polarisation experiments with short contact times. Therefore, multinuclear NMR spectroscopy, and in particular the measurement of both isotropic and anisotropic parameters, offers a useful tool for the structural study of ordered and, in particular, disordered ZIFs.Publisher PDFPeer reviewe

Phase distribution, composition and disorder in Y2(Hf,Sn)2O7 ceramics : insights from solid-state NMR spectroscopy and first-principles calculations

The authors would like to thank the ERC (EU FP7 Consolidator Grant 614290 “‘EXONMR’”), and EPSRC for support for SS and ASG (EP/L005581/1). SEA would like to thank the Royal Society and Wolfson Foundation for a merit award. We acknowledge support from the Collaborative Computational Project on NMR Crystallography CCP-NC funded by EPSRC (EP/M022501/1).A NMR crystallographic approach, combining 89Y, 119Sn and 17O NMR spectroscopy with X-ray diffraction and first-principles calculations has been used investigate the number and type of phases present, and the local structure and disorder in Y2Hf2–xSnxO7 ceramics. Although a phase change is predicted with increasing Hf content, NMR spectra clearly show the presence of a significant two-phase region, with a Sn-rich pyrochlore and relatively Hf-rich defect fluorite phase co-existing for much of the compositional series. A single-phase pyrochlore is found only for the Sn end member, and a single defect fluorite phase only for x = 0 to 0.2. A solid-solution limit of ~10% is seen for the substitution of Hf into Y2Sn2O7, although no evidence is seen for any cation ordering or antisite disorder in this phase. In the defect fluorite phase there is preferential ordering of oxygen vacancies around Sn, which is only ever seen in a six-coordinate environment. The remaining vacancies are more likely to be associated with Hf than with Y, although this distinction is less apparent at higher Sn concentrations. To acquire 17O NMR spectra samples were post-synthetically exchanged with 17O2(g), although high temperatures (> 900 ºC) were required to ensure uniform enrichment of different chemical species. although these 17O NMR spectra confirm the formation of mixed-metal materials and the presence of two phases, more quantitative analysis is hindered by the overlap of signals from pyrochlore and defect fluorite phases. In all cases, DFT calculations play a vital role in the interpretation and assignment of the NMR spectra, and in understanding the local structure and disorder in these complex multi-phase materials.PostprintPostprintPeer reviewe

Sensitivity of material failure to surface roughness: a study on titanium alloys Ti64 and Ti407

The relationship between material failure and surface roughness has been investigated using two titanium alloys: Ti64 and the more ductile Ti407. Three surface types were created (polished, sandblasted and scratched) with instances spanning a wide range of average roughness. The surfaces were tested in three-point bending with the imparted roughness on the tensile under-surface of a rectangular beam specimen. Results showed failure of Ti64 to be highly sensitive to both magnitude and orientation of roughness. High roughness in the maximum tensile stress direction (and scratch like features perpendicular to this direction) were most detrimental. Thus, strain-to-failure (and work-to-failure) in Ti64 dropped off significantly with increasing surface roughness in the tensile direction. Finite element modelling of the test indicated that cracks initiate at zones of high plastic strain at the tips of roughness valleys due to high local surface curvature. Thus, roughness can be considered as a series of blunt crack-like features where larger crack tip curvature induces greater likelihood of crack propagation. Contrastingly, the mechanical response of Ti407 was insensitive to surface roughness owing to its significantly greater ductility. Thus, designers need to be aware of the sensitivity of failure of particular materials to surface roughness. The insensitivity of Ti407 is advantageous, but the sensitivity of failure to surface roughness in a material like Ti64 is potentially serious if not properly accounted for

Phenotypic and genetic analysis of milk and serum element concentrations in dairy cows

This research, including the Langhill experiment at Crichton Dairy Research Centre and all authors, was funded by the Scottish Government Rural Affairs, Food and the Environment (RAFE) Strategic Research Portfolio 2016-2021. Samples collected pre-2016 were collected as part of a BBSRC project awarded to EW (grant no. BB/K002260/1) and TNM (BB/K002171/1). The authors gratefully acknowledge the high standard of work by all staff at Crichton farm (SRUC, Dumfries, Scotland) in the collection of samples and management of animals, and Ian Archibald (SRUC, Edinburgh, Scotland) for managing the Langhill database and assisting with data extraction.Peer reviewedPublisher PD