Combined theoretical and experimental investigations of porous crystalline materials

This thesis combines solid-state nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), chemical synthesis, isotopic enrichment and density-functional theory (DFT) calculations to provide insight into a number of microporous materials. The first class of materials studied is metal-organic frameworks (MOFs), where the presence of paramagnetic ions has a range of effects on the ¹³C NMR spectra, depending on the nature of the ligand-metal interactions. For the Cu²⁺-based MOFs, HKUST-1 and STAM-1, the assignment of the NMR spectra is non-intuitive, and unambiguous assignment requires specific ¹³C labelling of the organic linker species. It is shown that ¹³C NMR spectra of these two MOFs could act as a sensitive probe of the nature of “guest” molecules bound to the Cu²⁺. The second class of materials is aluminophosphates (AlPOs). It is shown that, using a series of relatively simple linear relationships with the crystal structure, the NMR parameters calculated by DFT (with calculation times of several hours) can be predicted, often with experimentally-useful accuracy, in a matter of seconds using the DIStortion analysis COde (DISCO), which is introduced here. The ambient hydration of the AlPO, JDF-2, to AlPO-53(A) is shown to occur slowly, with incomplete hydration after ~3 months. The resulting AlPO-53(A) is disordered and some possible models for this disorder are investigated by DFT. The final class of materials is gallophosphates (GaPOs), particularly GaPO-34 and related materials. The two as-prepared forms of GaPO-34 are characterised by solid-state NMR, and their calcination investigated by TGA and in-situ powder XRD. An unusual dehydrofluorinated intermediate phase is isolated and characterised for the first time by solid-state NMR. The fully calcined material is shown to be stable under anhydrous conditions, but hydrates rapidly in air. The hydrated material is stable under ambient conditions, but collapses upon heating. Partial dehydration without collapse is achieved by gentle heating or room-temperature evacuation. The impurity phases, GaPO₄ berlinite and GaPO-X are investigated by solid-state NMR and, while the structure of GaPO-X remains unknown, much structural information is obtained

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

Investigating FAM-N pulses for signal enhancement in MQMAS NMR of quadrupolar nuclei

The authors would like to thank EPSRC (EP/K503162/1) for the award of a studentship to HFC and the ERC (EU FP7 Consolidator Grant 614290 “EXONMR”) for support. SEA would also like to thank the Royal Society and Wolfson Foundation for a merit award. The UK 850 MHz solid-state NMR Facility used in this research was funded by EPSRC and BBSRC (contract reference PR140003), as well as the University of Warwick including via part funding through Birmingham Science City Advanced Materials Projects 1 and 2 supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF). Financial support from the TGIR-RMN-THC Fr3050 CNRS to access the 800 MHz spectrometer (Lille) is gratefully acknowledged.Although a popular choice for obtaining high-resolution solid-state NMR spectra of quadrupolar nuclei, the inherently low sensitivity of the multiple-quantum magic-angle spinning (MQMAS) experiment has limited its application for nuclei with low receptivity or when the available sample volume is limited. A number of methods have been introduced in the literature to attempt to address this problem. Recently, we have introduced an alternative, automated approach, based on numerical simulations, for generating amplitude-modulated pulses (termed FAM-N pulses) to enhance the efficiency of the triple- to single-quantum conversion step within MQMAS. This results in efficient pulses that can be used without experimental reoptimisation, ensuring that this method is particularly suitable for challenging nuclei and systems. In this work, we investigate the applicability of FAM-N pulses to a wider variety of systems, and their robustness under more challenging experimental conditions. These include experiments performed under fast MAS, nuclei with higher spin quantum numbers, samples with multiple distinct sites, low-γ nuclei and nuclei subject to large quadrupolar interactions.Publisher PDFPeer reviewe

MC2^2: Subaru and Hubble Space Telescope Weak-Lensing Analysis of the Double Radio Relic Galaxy Cluster PLCK G287.0+32.9

The second most significant detection of the Planck Sunyaev Zel'dovich survey, PLCK~G287.0+32.9 ($z=0.385$) boasts two similarly bright radio relics and a radio halo. One radio relic is located $\sim 400$ kpc northwest of the X-ray peak and the other $\sim 2.8$ Mpc to the southeast. This large difference suggests that a complex merging scenario is required. A key missing puzzle for the merging scenario reconstruction is the underlying dark matter distribution in high resolution. We present a joint Subaru Telescope and {\it Hubble Space Telescope} weak-lensing analysis of the cluster. Our analysis shows that the mass distribution features four significant substructures. Of the substructures, a primary cluster of mass $M_{200\text{c}}=1.59^{+0.25}_{-0.22}\times 10^{15} \ h^{-1}_{70} \ \text{M}_{\odot}$dominates the weak-lensing signal. This cluster is likely to be undergoing a merger with one (or more) subcluster whose mass is approximately a factor of 10 lower. One candidate is the subcluster of mass$M_{200\text{c}}=1.16^{+0.15}_{-0.13}\times 10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}$located$\sim 400$kpc to the southeast. The location of this subcluster suggests that its interaction with the primary cluster could be the source of the NW radio relic. Another subcluster is detected$\sim 2$Mpc to the SE of the X-ray peak with mass$M_{200\text{c}}=1.68^{+0.22}_{-0.20}\times 10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}$. This SE subcluster is in the vicinity of the SE radio relic and may have created the SE radio relic during a past merger with the primary cluster. The fourth subcluster,$M_{200\text{c}}=1.87^{+0.24}_{-0.22}\times 10^{14} \ h^{-1}_{70} \ \text{M}_{\odot}$, is northwest of the X-ray peak and beyond the NW radio relic.Comment: 19 pages, 14 figures; Accepted to Ap

Ionothermal synthesis and characterization of CoAPO-34 molecular sieve

The cobalt-doped aluminophosphate molecular sieve, CoAPO-34 (with the chabazite-type topology) was prepared under ionothermal conditions using 1-ethyl-3-methylimidazolium bromide (EMIMBr) ionic liquid in presence of 1,6-hexanediamine (HDA). The HDA is not incorporated in CoAPO-34, but is required to mediate the availability of Co2+ during the synthesis. The material was characterized using powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and solid-state NMR spectroscopy. Wideline 31P NMR spectroscopy showed broad signals (∼5000–10000 ppm wide), confirming that paramagnetic cobalt ions are successfully incorporated within the framework of the materials.PostprintPeer reviewe

The ambient hydration of the aluminophosphate JDF-2 to AlPO-53(A):insights from NMR crystallography

The aluminophosphate (AlPO) JDF-2 is prepared hydro­thermally with methyl­ammonium hydroxide (MAH+·HO-, MAH+ = CH3NH3+), giving rise to a microporous AEN-type framework with occluded MAH+ cations and extra-framework (Al-bound) HO- anions. Despite the presence of these species within its pores, JDF-2 can hydrate upon exposure to atmospheric moisture to give AlPO-53(A), an isostructural material whose crystal structure contains one mol­ecule of H2O per formula unit. This hydration can be reversed by mild heating (such as the frictional heating from magic angle spinning). Previous work has shown good agreement between the NMR parameters obtained experimentally and those calculated from the (optimized) crystal structure of JDF-2. However, several discrepancies are apparent between the experimental NMR parameters for AlPO-53(A) and those calculated from the (optimized) crystal structure (e.g. four 13C resonances are observed, rather than the expected two). The unexpected resonances appear and disappear reversibly with the respective addition and removal of H2O, so clearly arise from AlPO-53(A). We investigate the ambient hydration of JDF-2 using qu­anti­tative 31P MAS NMR to follow the transformation over the course of 3 months. The structures of JDF-2 and AlPO-53(A) are also investigated using a combination of multinuclear solid-state NMR spectroscopy to characterize the samples, and first-principles density functional theory (DFT) calculations to evaluate a range of possible structural models in terms of calculated NMR parameters and energetics. The published structure of JDF-2 is shown to be a good representation of the dehydrated material, but modification of the published structure of AlPO-53(A) is required to provide calculated NMR parameters that are in better agreement with experiment. This modification includes reorientation of all the MAH+ cations and partial occupancy of the H2O sites

Thermal dehydrofluorination of GaPO-34 revealed by NMR crystallography

SEA thanks the Royal Society and the Wolfson Foundation for a merit award. The UK 850 MHz solid-state NMR Facility used in this research was funded by EPSRC and BBSRC (contract reference PR140003), as well as the University of Warwick including via part funding through Birmingham Science City Advanced Materials Projects 1 and 2 supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF). We acknowledge support from the Collaborative Computational Project on NMR Crystallography CCP-NC funded by EPSRC (EP/M022501/1).Using a combination of solid-state NMR spectroscopy, powder X-ray diffraction (pXRD), thermogravimetry, and periodic density functional theory (DFT) calculations, we investigate the calcination of the chabazite-type gallophosphate, GaPO-34, prepared with either 1-methylimidazole (mim) or pyridine (py) as the structure-directing agent (SDA) and fluoride as the charge-balancing anion. We demonstrate that, prior to SDA combustion, there is an unusual low-temperature dehydrofluorination step at ∼330 °C for the mim material, but not for the py form. The DFT-derived structure for the dehydrofluorinated intermediate contains pentacoordinate Ga species with Ga–N bonds of 2.04 Å to the mim nitrogen atom, in addition to four Ga–O bonds to neighboring PO4 tetrahedra. This observation is consistent with 71Ga NMR spectroscopy, which shows that one-third of the Ga is pentacoordinate with a large quadrupolar coupling constant of ∼11 MHz. Powder X-ray diffraction measured in situ on heating shows the transient appearance of a distinct crystalline phase between 325 and 425 °C before the characteristic chabazite structure is seen, which is consistent with dehydrofluorination prior to loss of the organic SDA. No such dehydrofluorinated intermediate structure is observed for the py form of GaPO-34, which is ascribed to the lower pKa of pyridinium relative to 1-methylimidazolium.PostprintPostprintPeer reviewe

Synthesis and polymorphism of mixed aluminium-gallium oxides

DSC is grateful to the EPSRC for award of an industrial CASE studentship, partly funded by Johnson Matthey plc. SEA, DMD and JEH thank the ERC (EU FP7 Consolidator Grant 614290 “EXONMR”) for funding. SEA would also like to thank the Royal Society and Wolfson Foundation for a merit award.The synthesis of a new solidsolution of the oxyhydroxide Ga5–xAlxO7(OH) isinvestigated via solvothermalreaction between gallium acetylacetonate and aluminium isopropoxide in1,4-butanediol at 240 °C. A limited compositional range 0 ≤ x ≤ 1.5 is produced, with the hexagonalunit cell parameters refined from powder X-ray diffraction (XRD) showing alinear contraction in unit cell volume with increasing Al content. Solid-state 27Aland 71Ga NMR spectroscopy show a strong preference for Ga to occupythe tetrahedral sites and Al to occupy the octahedral sites. Using isopropanolas the solvent, g-Ga2–xAlxO3defect spinel solid solutions with x ≤ 1.8 can be prepared at 240 °C in24 hours. These materials are nanocrystalline, as evidenced by their broaddiffraction profiles, but the refined cubic lattice parameter shows a linearrelationship with the Ga:Al content and solid-state NMR spectroscopy again showsa preference for Al to occupy the octahedral sites. Thermal decomposition ofthe Ga5–xAlxO7(OH)occurs via poorly ordered materials that resemble e-Ga2–xAlxO3and k-Ga2–xAlxO3,but g-Ga2–xAlxO3transforms above 750 °C to monoclinic b-Ga2–xAlxO3for 0 ≤ x ≤ 1.3 and to hexagonal a-Ga2–xAlxO3for x = 1.8, with intermediate compositions 1.3 < x < 1.8 giving mixturesof the aand b polymorphs.Solid-state NMR spectroscopy shows only the expected octahedral Al for a-Ga2–xAlxO3and, for b-Ga2–xAlxO3,the ~1:2 ratio of tetrahedral:octahedral Al is in good agreement with Rietveldanalysis of the average structures against powder XRD data. Relative energiescalculated by periodic density functional theory (DFT) confirm that there is a~5.2 kJ mol–1 penalty for tetrahedral rather than octahedral Al inGa5–xAlxO7(OH), whereas this penalty is muchlower (~2.0 kJ mol–1) for b-Ga2–xAlxO3,in good qualitative agreement with the experimental NMR spectra.PostprintPeer reviewe

Evening electronic device use and sleep patterns in athletes

The present study aimed to investigate pre-sleep behaviours (including evening electronic device use) and sleep quantity in well-trained athletes. Seventy well-trained athletes (44 females, 26 males) aged 21 ± 4 y from a range of team and individual sports were asked to complete an online sleep diary for 7 days. The sleep diary included questions about pre-sleep behaviours (e.g. napping, caffeine intake), electronic device use in the 2 h prior to bedtime (e.g. type of device and duration of use) and sleep (e.g. time in bed, sleep onset latency). On average, athletes spent 8:20 ± 1:21 h in bed each night. Associations between age, time in bed and sleepiness suggested that younger athletes spent more time in bed (B = -0.05, p = 0.001) but felt sleepier (r = -0.32, p &lt; 0.01) than older athletes. On average, athletes mostly used electronic devices for 0–30 min prior to sleep. The use of multiple devices in the evening was associated with more perceived difficulty in falling asleep (B = 0.22, p = 0.03), but no associations existed with other sleep variables. In summary, younger athletes may require later start times or improved sleep quality to resolve excessive sleepiness