1,721,562 research outputs found
SmartLab: some initial results and experiences
No full textSmartLab configuration. Micro diffraction. Texture – pole figures. In-plane diffraction. Epitaxy - RSM
Automating the single crystal x-ray diffraction experiment
No full textEver decreasing data collection times and an explosion in demand present us with the situation where an automated single crystal instrument is not only advantageous but essential. With recent developments in software, instrumentation and robotics it has been possible to fully automate structure determination from mounted crystal to completed crystal structure. In Southampton we have developed a system that takes pre-mounted samples, loads them onto the diffractometer, assesses their diffraction quality, determines the unit cell, calculates and performs the data collection, carries out data reduction, and finally solves and refines the structure.The data collection procedures are built around and adapted from the Collect suite of programs. The structure solution and refinement is based on the SHELX suite of programs and emulates the decision making processes of a human crystallographer. Throughout the development of the system the emphasis has continually shifted as potential pitfalls were uncovered and then solved. These included crystal mounting, scan parameter calculation, collision security, space-group determination and atom typing
Crystallite size determination: a comparison of approaches and methods
No full textCrystallite size determination based on diffraction peak broadening is a widely used technique with its origins dating back to 1918 and the publication of Scherrer’s eponymous equation. Over the years the analysis of line broadening has become more refined and various methods and approaches have been adopted. These range from single peak analysis to full pattern fitting and fundamental parameter approaches. The key to all these methods is the correct characterisation of the instrumental broadening of the diffractometer and an appreciation of the likely microstructure of the sample.This work will present a comparison of the various approaches currently available to researchers and attempt to validate these against other methods such as Scanning Electron Microscopy. It will aim to give a sense of the reliability of the method and provide limits within which the results can be sensibly interpreted
Automating the Single Crystal X-Ray diffraction Experiment
No full textThe advent of CCD detectors and bright lab X-ray sources has accelerated the diffraction experiment to a point where a small molecule data set can be collected in as little as a few minutes, or more routinely in a few hours. Thus, to fully utilise the instruments capability some level of automation is essential. In our lab in Southampton we have taken the approach of automating the entire process, from mounted crystal to refined structure. A pre-mounted sample from a rack of 24 is loaded onto a Kappa CCD diffractometer by a BruNo sample changing robot. Prescans are performed to asses the crystal diffraction quality and, if favourable, a unit cell is determined. Data collection is carried out using a calculated strategy based on the diffracting power of the crystal and the unit cell dimensions. Data reduction takes place as a parallel process and finally the structure is solved and refined. Key points in the development of the system included the automation of the diffraction experiment, intelligent decision making, integration of the diffractometer and sample changing robot, automation of structure solution and refinement, and development of a controlling GUI. The automation software is written in PYTHON and utilises the documented diffractometer control and data collection software modules of COLLECT [1]. This made possible the full integration of the system flow between the robot and diffractometer and substitution of all required user inputs. A user interface, X-Tray, has been written to initialise the experiment and set various global parameters. The structure solution and refinement program, SYSTEM-Y, is written in FORTRAN and is based on the SHELX [2] suite of programs. <br/
Structural studies of mineral silicates and synthetic sulfosalts characterised by mixed occupancies
No full textIn the first part of this study are presented the synthesis and results of structural investigations of mixed metal sulfosalts. Included are the structures of five new lead, bismuth and antimony sulfosalts; phase GZ1 (Bi4.39 Pb1.4 Sb3.21 S13), phase GZ2 (Bi1.74 Pb2.62 Sb2.15 S8), phase GZ3 (Bi0.87 Pb1.22 Sb0.42 S3), phase GZ4 (Sb4.66 Pb3.97 Bi1.37 S13) and phase GZ5 (Sb6 Pb14 S23), and the revaluation of the known phases zinckenite (Pb1.49 Sb3.64 S7), stibnite (Sb2 S3), lillianite (Pb3 Bi2 S6) and galenobismutite (Pb Bi2 S4). With the exception of stibnite and galenobismutite these phases are characterised by mixed occupancies, and the site populations were assigned via a combination of microprobe analyses, polyhedral distortion and bond valence analysis results. To this end two FORTRAN programs were written, OCCGEN96 and VOLUME96, the former to calculate the occupancy of a site based on the bond valence contributions of its constituents, and the latter to calculate its polyhedral volume. Phase GZ1 exhibits a monoclinic structure with a central region reminiscent of stibnite, and its distribution of occupancies indicate the presence of a supercell produced by ordering. Phases GZ2 and GZ3 are hexagonal with features in common with zinckenite. GZ3 possesses the smallest hexagonal cell yet found for a sulfosalt and its structure contains three-fold metallic columns, in addition it displays a metal coordination environment not previously seen in this type of structure. The positional disorder, and partial occupancies (manifest as poorly defined hexagonal channels) exhibited by zinckenite and the other hexagonal sulfosalts are here explained for the first time in terms of alternately occupied configurations arranged on a superlattice. Phase GZ5 resulted from an attempt to crystallise the mineral semseyite whose structure is unknown, but possibly closely related to that of GZ5. The poorly defined phases from the literature have all been refined with better discrepancy indices and in the case of lillianite the results differ significantly from those previously reported. Additional investigations of phase GZ1 were carried out using transmission electron microscopy, and these lead to the identification of a number of related phases and also revealed the presence of disordered and composite structures. In the second part of the study diamond inclusions of lower mantle origin are investigated. In common with the sulfosalts they are characterised by mixed occupancies, however the distribution of metal species within mineral silicates is better understood than in sulfosalts, and they provided a good base from which to study the latter. The presented results include the crystal structure of the new mineral TAPP (Mg0.76 Fe0.15) (Al1.76 Cr0.16 Mn0.06) (Mg1.88 Fe0.08) Si1 (Si1.92 Al0.08) O12, which is of great significance in lower mantle genesis theory; the structures of two novel pyroxenes (Mg0.46 Al0.43 Fe0.06 Cr0.05) (Mg0.39 Na0.31 Ca0.16 Fe0.06 Mn0.04) (Si1.91 Al0.09) O6 and (Mg0.73 Al0.23 Cr0.03) (Mg0.70 Na0.06 Ca0.03 Fe0.16 Mn0.04) (Si0.83 Al0.17) SiO6 and the only sapphire (Al1.98Fe0.01Si0.01O3) to be found as a diamond inclusion. The structure of TAPP is particularly interesting as it has a garnet composition but is tetragonal not cubic. In the past the only non cubic garnets have been so only by a few angstroms at the most, while the cell of TAPP has a c parameter nearly three times that of a
Synergistic catalysis: cis-cyclopropanation of benzoxazoles
No full textIn the present paper we report our latest efforts in pushing the boundaries of Synergistic Catalysis. We propose the use of 3 different catalytic cycles working in concert for the formation of cis cyclopropane derivatives of benzoxazoles with excellent stereoselectivities. This is the proof of concept that synergistic catalysis could be successfully used in cascade reaction
Dataset: Instrument Development and a Total Scattering Investigation of Aqueous Magnesium Sulfate
No full textData to accompany the Southampton University Doctoral thesis titled 'Instrument Development and a Total Scattering Investigation of Aqueous Magnesium Sulfate'
Data included is RAW scattering data, processed scattering data and various refinements. </span
Synthesis of ortho-functionalized 1,4-cubanedicarboxylate derivatives through photochemical chlorocarbonylation
No full textThe cubane ring has received intense attention as a 3D benzene isostere and scaffold. Mono- and 1,4-disubstituted cubanes are well-described. Here we report a practical procedure for a direct radical-mediated chlorocarbonylation process initially reported by Bashir-Hashemi, to access a range of 2-substituted 1,4-cubanedicarboxylic ester derivatives. A subsequent regioselective ester hydrolysis to give fully differentiated 1,2,4-trisubstituted cubanes is demonstrated
Protonation-triggered conformational modulation of an N,N?-dialkylbispidine: first observation of the elusive boat–boat conformer
No full textModulation of the solution conformations of N,N?-bis(benzhydryl)bispidine has been achieved by protonation. Conformers have been characterized by NMR spectroscopy using nuclear Overhauser effects and residual dipolar couplings. In contrast to the preference for the chair–chair conformation for the free base and the monoprotonated species, the diprotonated bispidine is revealed to exist as a mixture of chair–boat and boat–boat conformers. While boat–boat conformers of bispidines have previously not been detected, they are here observed to constitute up to 70% of the bispidine population
Interactions of organic halide and nitrate salts with meso-octamethylcalix[4]pyrrole
No full textProton NMR titrations have been performed with meso-octamethylcalix[4]pyrrole and a variety of organic chloride and bromide salts in dichloromethane-d2. The results show apparently increasing chloride stability constants within each set of anion salts (tetrabutylammonium < imidazolium < pyridinium). Addition of 1-ethyl-3-methylimidaolium (EMIM) nitrate to dichloromethane-d2 solutions of calix[4]pyrrole caused significantly larger downfield shifts of the pyrrole NH protons of calix[4]pyrrole than addition of equimolar quantities of tetrabutylammonium nitrate. The first crystal structure of a nitrate complex of a calix[4]pyrrole is also presented
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