1,721,395 research outputs found
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
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/
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
A Fully Automated Small Molecule Single Crystal X-Ray Diffraction System: poster
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 desirous but essential. This poster presents our new system that has been developed around a Bruker Nonius Kappa CCD diffractometer and a Mitsubishi Movemaster RV-1A industrial robot, affectionately know as BruNo.
The Bruker Nonius control software, COLLECT[1], supports access to its methods and functions and along with its programmers documentation has made possible the integration of the diffractometer with the sample changing robot. In addition it has enabled the streamlining of the data collection procedure to an intelligent but completely automated state.
The current setup utilises a rack of 24 premounted samples that can be run with no user intervention from crystal quality evaluation to completed structure. The experiment is run from a virtual sample pallet where sample pertinent data can be rapidly entered, and global parameters set. The fist sample is subsequently mounted by BruNo and series of prescans performed to determine the diffraction characteristics of the crystal. The unit cell is determined and further image analysis carried out to select optimal parameters for the data collection. Once this is complete the data processing is spawned off as a separate process and the resultant files fed to Dr Yang Li’s automatic crystal solution and refinement package. Meanwhile, the next sample has already begun its journey through the same set of processes.
As well as routine data collections this system is ideal for screening polymorphs and solvates and searching for that elusive good crystal from a bad bunch
Solvent-induced supramolecular isomerism in Pt(S=C(NH2)(2))(4) (2+) croconate salts
No full textThe role of solvent (and other species) in the formation of networks from tetrakis(thiourea) platinum(II) cations and croconate anions is examined, with crystallisations from DMSO giving rise to a structure containing solvent filled channels
Network formation by a pyrrole functionalized isophthalamide
No full textN1, N3-Bis(2,4-diphenyl-1H-pyrrol-3-yl) benzene-1,3-dicarbamide forms a network containing clusters of water molecules when crystallized from wet methanol
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
Phosphine complexes of aluminium(iii) halides – preparation and structural and spectroscopic systematics
No full textSix-coordinate pseudo-octahedral complexes trans-[AlX2(L–L)2][AlX4] (X = Cl, Br or I; L–L = o-C6H4(PMe2)2, Me2P(CH2)2PMe2) are produced from reaction of AlX3 with the diphosphine in CH2Cl2 (X = Cl) or toluene (X = Br or I) solution. Four-coordinate dimers [Cl3Al(?-L?–L?)AlCl3] (L?–L? = Me2P(CH2)2PMe2, Cy2P(CH2)2PCy2), and the tetrahedral cation [AlCl2{o-C6H4(PPh2)2}][AlCl4] were also obtained. Both four- and five-coordinate complexes [AlX3(PMe3)] and [AlX3(PMe3)2] could be isolated with PMe3 depending upon the ratio of reagents used. These extremely moisture sensitive complexes have been characterised by microanalysis, IR and multinuclear NMR (1H, 31P{1H} and 27Al) spectroscopy. X-ray crystal structures are reported for [AlCl2{o-C6H4(PMe2)2}2][AlCl4], [AlCl2{Me2P(CH2)2PMe2}2][AlCl4], [Cl3Al{?-Me2P(CH2)2PMe2}AlCl3], [Cl3Al{?-Cy2P(CH2)2PCy2}AlCl3], [AlCl3(PMe3)], [AlCl3(PMe3)2], and for the six-coordinate cation complex [AlCl2{o-C6H4(PPh2)2}2][AlCl4], although a bulk sample of the last could not be isolated. Tertiary arsines (AsPh3 or AsEt3) form only 1 : 1 complexes even with excess arsine present. The unstable [AlCl2{o-C6H4(AsMe2)2}][AlCl4] is also described, and shown to decompose rapidly in CH2Cl2 solution to form the diquaternised diarsine cation [o-C6H4(AsMe2)2(CH2)][AlCl4]2, which was fully characterised. Comparisons are drawn with the corresponding gallium(III) systems (Cheng et al., Inorg. Chem., 2007, 46, 7215–7223) and with AlX3 complexes of Group 16 ligands (George et al., Dalton Trans., 2014, 43, 3637–3648), and it is concluded that the differences between the Al and Ga systems reflect the higher Lewis acidity of aluminium(III) towards soft donor ligands
Tetrakis(thiourea) platinum(II) oxocarbodianions salts as molecular building blocks for the synthesis of hydrogen bonded networks in the solid state
No full textCrystallization of tetrakis(thiourea) platinum(II) with squarate, croconate and rhodizonate dianions leads to the formation of different hydrogen bonded networks. The solvent used in the crystallization plays a central role in the nature of the hydrogen bonded network obtained, templating different structures from the same molecular building blocks
Structure of framboidal pyrite: a single crystal X-ray diffraction study
No full textThe crystallographic nature of pyrite framboids, self-assembled multicrystalline pyrite, was investigated by single crystal X-ray diffraction. The results show that even morphologically well-organised framboids are not extreme examples of single crystals but are microcrystalline aggregates. Two dimensional diffraction patterns obtained from well-organised framboids composed of relatively few (~1000) microcrystals, are single-crystal like but detailed analysis shows that they are actually produced by the superimposition of XRD reflections from similarly, but not identically, oriented microcrystals. The number of coherent crystallographic orientations of pyrite crystals estimated from a complete Ewald sphere data set obtained from a larger single framboid, were found to be approximately four to five times fewer than the number of the microcrystals that are actually contained in the framboid. The result shows the presence of multiple single crystal-like domains that are arranged in similar crystallographic orientations. The results show that framboids are not formed by a process in which crystallographic control is a primary factor. Framboid self-assembly is probably caused by the aggregation of a large number of similarly sized and shaped pyrite microcrystals that are nucleated in a limited volume. Self-organisation occurs as these microcrystals adopt a minimum energy configuration
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