bluuebunny/crossref_metadata_2025 huggingface dataset:
Cyclodextrin inclusion complexes of the antioxidant α-lipoic acid
Authors: Caira Mino , Bourne Susan , Mzondo Buntubonke
Published: November 2015

Owing to its potent antioxidant activity,α-lipoic acid (1,2-dithiolane-3-pentanoic acid) is widely used as a supplement and is recommended for treating a number of conditions including chronic liver disease and diabetes. The poor aqueous solubility of the acid (~0.003 M at 250C) has prompted studies of its interaction with cyclodextrins (CDs) as a possible route to improving its solubility. However, relatively few studies have focused on the isolation of solid CD inclusion complexes of the antioxidant, and in most cases the racemic form of the acid was employed. In the comprehensive study reported here, the bioactive (R)-(+)-enantiomeric form of the molecule was used exclusively, resulting in the isolation and structural characterization of its inclusion complexes with each of the native host CDs (α-, β- and γ-CD) as well as permethylated α-CD (TRIMEA), permethylated β-CD (TRIMEB) and 2,6-dimethylated-β-CD (DIMEB). The α-CD complex crystallizes in the trigonal system, space group R32, with three independent CD molecules in the asymmetric unit and is not isostructural with any known CD complex while the β-CD complex crystallizes in the monoclinic system (C2). With the host γ-CD, an orthorhombic (pseudo-tetragonal) inclusion complex was identified, an unusual result as γ-CD complexes generally crystallize in the tetragonal space group P4212. The complexes with TRIMEA and TRIMEB crystallize in the orthorhombic system (P212121), the modes of inclusion of the (R)-(+)-α-lipoic acid molecule in the respective hosts being reversed: the guest molecule is fully encapsulated by the former host with the dithiolane ring located at the secondary rim, while in the latter host, the dithiolane ring rests on the concave surface of the host cavity at the primary side. A significant level of guest disorder was detected in the inclusion complex with DIMEB (P21). Thermal and phase-solubility analyses complemented the X-ray structural studies.
Melting point- solubility relations of cocrystals
Authors: Bathori Nikoletta
Published: November 2015

Active pharmaceutical ingredients (APIs) with poor physicochemical properties, such as solubility and stability, lead to the failure of many drug candidates. The design of a new solid form of these molecules, such as cocrystals may improve the required physical chemical property. The successful prediction of a new crystal structure has improved recently with the aid of high performance computing. However, the prediction of certain properties, such as solubility of the new solid form, is still a desired achievement. The melting point and solubility are crucial pharmaceutical properties related to the processability. The measurement of the melting point is a simple, fast and reliable analytical method. However, the measurement of the solubility is a more time consuming step. It is commonly accepted that a crystal with weak secondary interactions has a lower melting point and heat of fusion and is more soluble compared to those with stronger intermolecular interactions. The ultimate goal of the project is to find a link between the effortlessly detectable melting point and the more challenging solubility values by analysing and quantifying the intermolecular interactions in the cocrystal and turn the `guessing game' into a state where we are able to `dress' the API with the requested property via cocrystallisation. As a first attempt, we designed and synthesized a series of model cocrystals where the API is replaced by a simple chemical unit with restricted secondary interaction possibilities and conformational motions (bipyridine and its derivatives), while the cocrystallising compound was varied systematically (series of dicarboxylic acids). It is required that the type of possible intermolecular interactions are limited to make achievable the identification of the relevant differences in their strength, or their contribution to the overall changes observed during the subtle modification of the cocrystal. In the second phase, we have investigated more advanced pharmaceutical cocrystals with a variety of different additional intermolecular interactions to map the influence of these newly introduced functionalities. The solubility and melting point data were correlated to the qualitative and quantitative changes observed in the different type of secondary interactions in the crystal structures.
Structural studies in single and poly crystals of Yb(1-x)Tb(x)MnO3manganites
Authors: Bolívar Guarín Mónica , Andreeta Marcello , Novak Miguel , Speziali Nivaldo
Published: November 2015

Rare-earth manganites, RMnO3, have been object of intense theoretical and experimental research; mainly focused on the exotic properties observed in these materials. Ferroelectricity, ferromagnetism, superconductivity and multiferroicity are some of the properties observed in RMnO3, been the multiferroicity the most important phenomena of the parent manganites YbMnO3 and TbMnO3 [1]. The focus of the present work is to find correlations between structural characteristics and the physical properties of some type of ferroic materials. Polycrystalline perovskites of Yb1-xTbxMnO3 (x=0, 0.25, 0.50, 0.75 and 1) were synthesized using solid-state method. Single crystals of the same compounds are to be produced by LHPG (Laser Heated Pedestal Growth) [2]. In the present work structural studies at room temperature will be reported. Samples with x=0 and 1 crystallizes in the P63cm and Pnma space groups, respectively. In the case of mixed compounds attention was paid to the study of the phase coexistence as well as to the site occupancy shared between rare-earth Tb and Yb [3]. Magnetic studies using powder samples were not conclusive due to the high anisotropy observed in these materials. Single crystals are under production in order to allow magnetic directional studies and consequently to search for results that can be correlated to the crystal structure. Improvement has to be made in the rare-earth site occupancy model to better associate magnetic results with atomic positions and individual magnetic moments.
Drug-Design QSARs based on QTAIM Electron Localization/Delocalization Indices
Authors: Sumar Ismat , Matta Chérif
Published: November 2015

Following the lead of chemical graph-theoretical connectivity matrices, electron localization/delocalization matrices (LDMs) and their matrix-invariants derived forms will be introduced and shown to provide a faithfully encoding of the properties of the molecules by comparing with experiment. The matrix elements of an LDM are obtained from Bader's quantum theory of atoms in molecules (QTAIM) whereby the diagonal elements are the localization indices and the off diagonal elements are 1/2 of the delocalization indices. The sum of any row or column is the total electron population of a given atom while the sum of all sums is, of course, the total number of electrons in the molecule (N). The matrix is, thus, rich with electronic (and structural) information, implicitly and explicitly, and is conceivably useful in generating quantitative molecular descriptors for structure-to-activity relationship studies (QSAR). This talk will briefly review the uses and concepts of molecular electron density descriptors with emphasis on this new class of descriptors as a novel, possibly promising, possibility.
Invariom point charges
Authors: Orben Claudia , Dittrich Birger
Published: November 2015

The invariom database [1] is known to provide aspherical scattering factors for atoms in different chemical environments. It contains more than 1450 geometry optimized model compounds. Underlying the database is a formalism of assigning the atoms according to their local bonding situation. An atom in such a specific intramolecular environment is called an invariom (invariant atom) because the properties related to it are invariant of the molecule. Besides aspherical scattering factors this formalism, combined with a model compound database, automatically provides point charges for atoms in common organic compounds as soon as 3D-coordinates are available. This could be especially useful for improving molecular mechanics simulations based on force fields like AMBER [2] in drug development, where point charges often have to be established manually. The invariom classification accounts for a more detailed description than a general atom force field, especially for hydrogen atoms. These are closest to the molecular surface and have a big impact on intermolecular interactions. Since the database already contains optimized structures of model compounds and their electron density, it only takes a restrained fit to the electrostatic potential (resp) [3] to obtain charges, which were designed to be transferable and are therefore ideally suited for application in force fields. Amber suggests the use of hf/6-31g* resp computations. The model compounds in the invariom database have been optimized using more extensive basis sets and DFT (M06/TZVP). A revision of the database that can in principle cover elements up to Krypton will be provided. Results from invariom point charges are compared with those from existing methods. Furthermore, some improvements to the invariom notation will be discussed.
Structural analysis of new ligands against Schistosoma mansoni
Authors: Mafud Ana , Mascarenhas Yvonne
Published: November 2015

Natural compounds have been an alternative to treat several diseases. In this sense, epiisopiloturine (EPI) [1] is an alkaloid found in Pilocarpus microphyllus (Rutaceae) leaves, with anthelmintic activity in vitro [2] and in vivo (To be publish). Unfortunately, EPI is slightly soluble in water. To solve this question, complexes and new derivatives were synthetized. Here, we present a x-ray structural analysis of the compounds: EPICu (CCDC 947608), C64H42N8O23Cl2Cu, P21, and EPIZn (CCDC 959718) C32H36N4O6Cl2Zn, P212121, both complexes with anthelmintic activity; EpiiHCl (CCDC 945616), C16H18N2O3Cl, P21, a derivative with reduce anthelmintic activity even high solubility; and epiisopilosine, EPIss C16H18N2O3, (CCDC 957103), P212121, a new active compound found in the same leaves but seasonally. The ligands conformational analysis were determined using Density Functional Theory calculations with the operator correlation of Lee–Yang–Parr (B3LYP), 6-31G++ base set, implementing two functions of polarization (d,p), to obtain the molecular electrostatic potential map. X-ray powder diffraction and thermogravimetry analysis were also performed to EPIss. The dihedral angle between the benzene and imidazole rings is feature common to such compounds, which range from 3 to 73 degrees. It is interesting to observe that the dihedral angle may be associated with the activity of these compounds, as well as other factors, since the smaller the dihedral angle, the activity is increased, even taking into consideration the EPI to this study. To compare the structures of the ligands, they were aligned and the overlay optimizer was the augmented Lagrangian method (local, no-derivative), shown in Figure 1, EPICl in green, EPI in blue and EPIss in yellow. Results showed that hydrophobic regions are conservative except for EPIss, due to its larger volume. And it may be understood through the occurrence of the CH/pi intramolecular interactions in the crystal stacking, which guarantee the EPIss larger globularity. Experimental parameters for TGA curve indicates that EPIss degradation occurs in two steps, associated with an endothermic DTA signal. XRD were performed in order to exclude the occurrence of isoforms in the crystalline powder.
Charge density studies of interactions in macromolecules – the case of sunitinib
Authors: Malińska Maura , Jarzembska Katarzyna , Goral Anna , Kutner Andrzej , Woźniak Krzysztof , Dominiak Paulina
Published: November 2015

Electron density is a key factor in determining properties of molecules. Knowledge of the electron density distribution allows to determine not only the 3D structure of molecules, but also various one-electron properties (electric moments, electrostatic potential, electrostatic interaction energy, etc.). X-ray diffraction is a great tool for obtaining this kind of information. For macromolecules, however, quantitative determination of charge density from experiment is possible on rare occasions only. We will present that with the University at Buffalo pseudoatom database (UBDB) approach [1,2] it is now possible to reconstruct electron density of any macromolecular system for which atomic coordinates are available. The approach is fast and opens an excellent opportunity to investigate macromolecular complexes by means of topological analysis of electron density (and derivatives thereof), electrostatic interaction energy analysis, and many others. The results of our studies on sunitinib (SU) will illustrate the possibilities of the approach. SU is an inhibitor of tyrosine kinases and was approved as a drug in 2006. Comprehensive analysis of the SU malate crystal and SU complexes with a series of protein kinases was carried out. The high resolution single crystal X-ray measurement and UBDB approach served as the basis for the reconstruction of the charge density of SU and the protein complexes. Hirshfeld surface and topological analyses revealed a similar interaction pattern in the SU malate crystal to that in the protein binding pockets. SU forms nine preserved bond paths corresponding to hydrogen bonds and also to the C-H...O and C-H...π contacts common for all analyzed kinases. It interacts typically with similar electrostatic interaction energy with the studied proteins and can adjust its conformation to fit the binding pocket in a way to enhance the electrostatic interactions. Such behavior can be responsible for a broad spectrum of action of SU as kinase inhibitor.
Intercalation process of anticancer copper (II) complexes in DNA
Authors: Cortes-Guzman Fernando , García-Ramos Juan , Galindo-Murrillo Rodrigo , Moreno-Esparza Rafael , Ruiz-Azuara Lena , Gómez Rosa
Published: November 2015

Ternary Copper (II) Complexes (TCC) have shown cytotoxic, genotoxic, and antineoplastic activity in vitro and in vivo. There are evidences that these compounds interact directly with DNA but it is not clear how deep TCC penetrates into the DNA double helix and their specific interactions have not been established. Recently, our group found that the deoxyribose-phosphate group is the specific recognition site of TCC in DNA. Here we report a crystallographic and theoretical study to determine each step of intercalation process of TCC in DNA with the recognition site as starting point. On the basis of crystal structures, Molecular Dynamics, DFT calculations and Electron Density Analysis we found that the family of analyzed TCC prefers the sequence Thymine-Adenine-Thymine to start the insertion. The intercalation process consists of an opening of a base pair as the complex intercalates within a succession of axial ligand exchange. The copper center migrates from phosphate to ribose then to thymine and finally to adenine. It is possible that the biological activity of TCC is related to its capability to evert base pairs and perform the necessary migrations from the recognition site to the complete intercalation
Controlling Crystal Structure in Embedded Magnetic Nanoparticles
Authors: Baker Steve , Roy Mervyn , Binns Chris , Lees Martin
Published: November 2015

"Magnetic nanoparticles and nanocomposite materials have attracted much interest due to their novel magnetic behaviour, and their potential use in a range of applications. One of the main reasons for their novel magnetism, appreciated for some time, is the high proportion of under-coordinated atoms at the surface of nanoparticles. In the case of magnetic transition metals this leads to a narrowing of the 3d bands that are responsible for magnetism in these materials, leading to size-dependent nanoparticle properties. The atomic structure adopted by nanoparticles is also a key factor in determining their magnetism. Unlike in bulk materials atomic structure in nanoparticles can be changed more readily by, for example, embedding them in suitable matrix materials. Here we describe how a high level of control over crystal structure in nanoparticles can be achieved, using EXAFS to ""fingerprint"" their crystal structure, and show how this in turn leads to a high degree of control over nanoparticle magnetism. We describe a flexible co-deposition process based around a gas aggregation source, which enables a high degree of control over structure in transition metal nanoparticles embedded in various matrices. EXAFS experiments and analysis used to probe atomic structure in embedded Fe and Co nanoparticles are described [1]. Examples presented include the system of Fe nanoparticles embedded in a CuAu alloy matrix where we show that is not only the ability to change the atomic structure of embedded nanoparticles that is important but the ability to fine-tune their structure once changed [2]. In this case, this enables the atomic magnetic Fe moment to be fine-tuned to a value higher than in the bulk Fe structure, in agreement with theory. In some systems alloying at the particle/interface can be significant. We describe how this is the case for Fe nanoparticles in Pd [3], and how such alloying could be useful in forming magnetic nanocomposites with superior properties."
Analysis of hidden information - PLSR on XRD raw data
Authors: König Uwe , Degen Thomas , Beckers Detlef
Published: November 2015

Usually in XRPD we are paying lots of attention to accurately describe profile shapes. We do that to eventually extract/predict information from the full pattern using physical models and fitting techniques. Sometimes this approach is stretched to its limits. That usually happens, when no realistic physical model is available, or when the model is either too complex or doesn't fit to reality. In such cases there is one very elegant way out: multivariate statistics and Partial Least-Squares Regression. This technique is rather popular in spectroscopy as well as in a number of science fields like biosciences, proteomics and social sciences. PLSR as developed by Herman Wold [1] in 1960 is able to predict any defined property Y directly from the variability in a data matrix X. In the XRPD the rows of the data matrix used for calibration are formed by the individual scans and the columns are formed by all measured data points. PLSR is particularly well-suited when the matrix of predictors has more variables than observations, and when there exists multi-collinearity among X values. In fact with PLSR we have a full pattern approach that totally dismisses profile shapes but still uses the complete information present in our XRPD data sets. We will show a number of cases where PLSR was used to easily and precisely predict properties like crystallinity and more from XRPD data.
Looking beyond chemistry – XRD for exploration and processing of ores
Authors: König Uwe , Fransen Martijn
Published: November 2015

Decreasing ore qualities and increasing prices for raw materials require a better control of processed ore and a more efficient use of energy. Traditionally quality control in mining industries has relied on time consuming wet chemistry or the analysis of the elemental composition. The mineralogy that defines the physical properties is often monitored infrequently, if at all. The use of high speed detectors has turned X-ray diffraction (XRD) into an important tool for fast and accurate process control. XRD data and their interpretation do make the difference in the identification of minerals, in describing their distribution in ore bodies and in their beneficiation during processing. The use of modern techniques such Partial Least Square Regression (PLSR), Principal Component Analysis (PCA) or full pattern Rietveld quantification will be discussed during the presentation as well as the importance of adequate sampling and the correlation with sample chemistry. The practical use will be illustrated on case studies.
Battery research using synchrotron powder X-ray diffraction
Authors: Gu Qinfen , Brand Helen , Kimpton Justin
Published: November 2015

Research and development of rechargeable batteries is critical to meet the worldwide demand for clean and sustainable energy collection and storage. A vital part of this research is to get clear understanding of how the crystal structures of electrode materials affect the the resulting properties of the batteries. As structural changes in both the anode and cathode materials play an important role in overall battery performance, synchrotron powder X-ray diffraction (PXRD), with high beam flux and resolution, is an extremely useful tool for studying the battery both in-situ and ex-situ. Several simple in-situ cell designs have been designed for synchrotron PXRD measurement. The cell is available for researchers in the field of battery research. The effectiveness and simplicity of the cell design have been demonstrated at Powder Diffraction Beamline at Australian Synchrotron for several user groups. Case studies of analysis of the lithium insertion reaction for Li0.18Sr0.66Ti0.5Nb0.5O3 defect perovskite [1], crystal structure of Li4Ti5O12–xBrx electrode material [2] and LiNi1/3Mn1/3Co1/3O2 (NMC) as a new synthesized cathode material [3] will be discussed, respectively.
Bridging the gaps; imaging of catalytic materials under reaction conditions
Authors: Beale Andrew
Published: November 2015

Industrial catalysis utilizes mainly μm to mm-sized catalyst particles in catalytic reactors instead of powders since this minimizes problems associated with for example back pressure and clogging. In recent times, efforts have been made to study and characterize these `real life' single particles so as to determine the nature of chemical species present in 2D and 3D during various stages of the catalyst lifetime such as preparation, reaction and deactivation. Traditionally this sort of analysis is performed on ex situ samples using invasive approaches which often interfere with the chemical process under study and the subsequent conclusions that can be drawn. As a result there has been a recent move towards studying these processes non-invasively and where possible, dynamically in order to understand in detail how the chemistry evolves within catalyst particles and how this and the spatial distribution of the various chemical components influence catalytic behaviour. For this purpose we have developed synchrotron-based X-ray Computed Tomography imaging techniques for studying catalytic solids in real time in order to examine how the active phases form, how they behave under reaction conditions and why they eventually deactivate.
Borohydride - Oxide Isomorphism in Design of Energy Storage Materials
Authors: Černý Radovan , Schouwink Pascal
Published: November 2015

An increasing number of novel single, double and triple cation borohydrides has been structurally characterized in the last few years as hydrogen storage materials and solid state electrolytes for battery applications [1,2]. It is interesting to note that the majority of these novel metal borohydrides resemble structures of various metal oxides. This is not altogether surprising considering the fact that [BH4]-and O2-anions are isoelectronic. The particularity of the borohydride-oxide analogy is the double negative charge of O2-vs. the simply charged borohydride [BH4]-, this providing a superior structural flexibility in oxides with respect to mixed valence compounds. Though somewhat handicapped by its lower charge regarding this issue, the borohydride anion obtains its versatility as a building block due to being a non-spherical anion with a tetrahedral shape as opposed to the oxide, which is approximately spherical. This commonly results in a lower symmetry of the borohydride when compared to the related oxide, the prototype very often showing a close packing of a readily polarisable soft oxide anion. We will show by means of in-situ synchrotron X-ray powder diffraction and ab initio calculations in the solid state that structural distortions in metal borohydrides compared to oxide prototypes have their origin in close hydridic di-hydrogen contacts of repulsive nature. These contacts may be suggested as a tool to tailor the crystal symmetry in complex metal hydrides in the future. Nearly twice as big as the oxide, the borohydride anion allows for connectivities of the coordination polyhedra rarely observed among the oxides such as tetrahedral edge sharing. We will show how the borohydride-oxide isomorphism, and cationic heterovalent substitution allow the prediction and design of novel borohydrides with high hydrogen content or high cation mobility.
Symmetry and symmetry breaking during crystal growth
Authors: Vlieg Elias
Published: November 2015

Two cases of symmetry and its breaking will be discussed in the context of crystal growth: chirality and surfaces. Chiral symmetry is a particularly interesting form of symmetry in crystal growth that may even be directly related to the homochirality that is found in Nature. About 10% of the chiral compounds crystallize as so-called racemic conglomerates, i.e. as separate crystals with only left or only right-handed molecules. The first experiments of Pasteur on a tartaric acid salt were an example of this. When crystallizing such compounds, one would expect a (symmetric) 50:50 mixture of both types of crystals, but often this is not the case. We will discuss (1) the chiral symmetry breaking in such systems [1], (2) the formation of epitaxial conglomerates that partially hide the true symmetry and (3) a phase transition from a racemic crystal (with both left- and right-handed molecules in the unit cell) to a racemic conglomerate. X-ray diffraction is often insufficient to fully characterize such systems, and solid-state NMR and computer simulations yield important additional insights. The symmetry of a bulk crystal is by definition broken at its surface, and this can manifest itself in different ways. Muscovite mica, as an example, can be made extremely flat by cleaving and therefore the bulk glide plane symmetry can be lost at the surface [2]. Charge neutrality dictates the distribution of the ions at the surface of mica and seems to be determined by local variations in the Al/Si ratio that are invisible for X-ray diffraction. By isomorphous replacement of the topmost K ions, mica can be functionalized to specifically react with other compounds.
Study of hydrogen storage materials by neutron powder diffraction
Authors: Huot Jacques , Gosselin Catherine , Bibienne Thomas , Flacau Roxana
Published: November 2015

Metal hydrides are interesting materials from a fundamental as well as practical point of view. Hydrogen storage applications have been the main driving force of research on these materials but lately uses such as thermal storage are considered. In this presentation we will review the use of neutron diffraction for the development of new metal hydrides. Two systems will be presented: BCC solid solution alloys and FeTi alloy. Ti-based BCC solid solutions are promising material for hydrogen storage applications which need high volumetric capacity and room temperature operation. One system that has been considered is Ti-V-Cr. Using only X-ray diffraction for structural identification does not provide information about hydrogen localization. Therefore, neutron diffraction is essential for complete determination of this class of hydrides. We will present examples of Ti-V-Cr compounds doped with Zr-Ni alloy. The peculiarity of this type of alloy is that, for neutron diffraction, the scattering lengths of the elements almost cancel. Therefore, the neutron pattern of as-cast alloy shows very small Bragg peaks but the advantage is that the hydride for is very easy to see and analyze. Another good candidate for hydrogen storage applications is the intermetallic compound TiFe which operates at around room temperature (RT) under mild pressure conditions. However one disadvantage of TiFe alloy synthesized by conventional metallurgical method is its poor activation characteristics. The alloy reacts with hydrogen only after complicated activation procedure involving exposure to high temperature (~4000C) and high pressure for several days. Recently we found that by doping this alloy with Zr and Zr7Ni10 the activation could be easily done at room temperature. We present here a neutron diffraction study of these compounds that shows the structural difference between the activated compound and the one cycled under hydrogen.
Not quite the beginning: early days in 1970s Oxford
Authors: Evans Philip
Published: November 2015

In the early 1970s there were only a handful of protein crystallography groups in the world, and less than a dozen structures had been solved. Although we were missing many of the methods and facilities that we now take for granted, we did solve structures, albeit rather slowly, and we did get some things right. We worried about errors. We worried about how to collect the best intensity data, and how to reduce radiation damage, at that time by cooling to near 00. We appreciated the value of anomalous scattering in phasing, and tried to make the best use of it in the refinement of heavy atom parameters, allowing for the estimated errors. Simon French introduced us to the ideas of Bayesian statistics in dealing with noisy data. We saw the beginnings of molecular replacement as a method for structure solution. And we learnt how to collaborate on software development, which led to the start of the CCP4 project at the end of the decade.
The history of the PDB as a public resource for enabling science
Authors: Berman Helen
Published: November 2015

As the crystal structures of biological macromolecules were being determined, a new field of structural biology was born. Inspired by these new structures, the scientific community worked to establish a home to archive and share the data emerging from these experiments. The Protein Data Bank (PDB) was established in 1971 with seven structures. The PDB provides a repository for scientists who generate the data, and an access point for researchers and students to find the information needed to drive additional studies. Today, the PDB contains and supports online access to ~100,000 biomacromolecules that help researchers understand aspects of biology, including medicine, agriculture, and biological energy. The ways in which the interrelationships among science, technology, and community have driven the evolution of the PDB resource for more than forty years will be discussed. The PDB archive is managed by the Worldwide Protein Data Bank (wwpdb.org), whose members are the RCSB PDB, PDBe, PDBj and BMRB.
Resolution of a modulated structure by electron and powder X-ray diffraction
Authors: Lepoittevin Christophe , Leynaud Olivier
Published: November 2015

These past few years, many new structures have been solved using electron diffraction methods: zone axis precession electron diffraction (PED) and tomography in reciprocal space. Both methods enable to reduce importantly the multiple scattering, so that the reflection intensities can be used for structure determination by direct methods. The ferrite Sr25Fe30O77 belongs to a family of phases whose structures consist of an intergrowth of m perovskite layers with complex rocksalt type layers [1,2]. The compound of interest is the member m = 4 of this family and its structure has been solved by combining both electron diffraction methods cited above. This oxide crystallizes in an orthorhombic system with the sub-cell parameters a ≍ b ≍ 5.4 Å and c ≍ 42 Å in a F type lattice. The structure exhibits modulation along a axis with a modulation vector q = 2/5 a. The commensurate nature of the modulation enables to describe the structure in a supercell with the cell parameters a ≍ 27 Å, b ≍ 5.4 Å and c ≍ 42 Å. PED patterns were recorded in zone axis with a Spinning Star unit using a precession angle of 20. The intensities were extracted with CRISP software and the resulting dataset was then implemented in SIR2008 for structure solution. The tomography data collection, recorded by tilting manually every 0.5 degree from -30 to +30 degrees, was inserted in a "3D Electron Diffraction Tomography" software, which reconstructs the 3D reciprocal space and extracts automatically the reflection intensities. The intensity file was then used on SIR2008 for structure determination. In order to confirm and refine the structural model, a powder X-ray diffraction pattern was performed on a laboratory diffractometer with Cu Ka1 radiation. Cell parameters were refined with the WinPlotr and FullProf Softwares using both LeBail and Rietveld methods [3]. The structural model obtained with electron diffraction data was tried and confirmed as the correct structure by the Rietveld refinements.
Why powder diffractionists need help from electron crystallography
Authors: Xie Dan , Zones Stacey , Rea Thomas
Published: November 2015

Although X-ray powder diffraction (XPD) is used as a routine tool for solving crystal structures of polycrystalline materials, its weakness is obvious: not only is the phase information lost during the diffraction experiment, but reflections with similar d-spacings, which are well-separated in a single-crystal measurement, overlap in a powder pattern. These effects increase the difficulty of structure solution especially when dealing with complex structures. Compared to XPD, the advantages from electron microscopy are: (1) single-crystal electron diffraction data, either in 2-dimensional or 3-dimensional form, can be obtained from a very tiny crystallite in a powder sample; and (2) high-resolution images can be collected and used to extract phase information in reciprocal space or to provide a direct view of structural features (ordered and disordered) [1]. With the extra information supplied by electron microscopy, the limits of structure determination for polycrystalline materials can be extended [2]. Here we will present a few examples to demonstrate why powder diffractionists need help from electron microscopy and how to integrate these two techniques into the structure determination process.
Solution and solid state effects of coordinated ligands in rhenium (I) complexes
Authors: Schutte-Smith Marietjie , Visser Hendrik , Roodt Andreas
Published: November 2015

In the last few years the coordination chemistry of rhenium and technetium has gained major interest for the possible use in radiopharmacy, due to its compact size, its low positive charge, coordination properties, d6 low-spin configuration and significant stability. This interest was further fuelled when Alberto remarkably synthesized fac-[99mTc-(CO)3(H2O)3] from [99mTcO4]- in aqueous medium and under mild conditions. Several fac-[M(CO)3]+ (M = Re, 99mTc) type complexes have been synthesized to date with a large number of ligand systems.[1,2] The three labile aqua ligands on the starting synthon fac-[Re(CO)3(H2O)3]+ can easily be substituted by a variety and/or combinations of ligands producing stable compounds and potential radiopharmaceuticals with many different characteristics. Our interest focuses on the fac-[Re(CO)3]+ moiety and related compounds by adopting the [2+1] approach.[3] The solid state behaviour of the complexes are explored as well as different effects such as the charge of the complexes as well as the effect of different types of donor atoms and electron donating or withdrawing systems. The influence of coordinated bidentate ligands on the rate of substitution in solution, by a variety of entering ligands, is also investigated. Crystal structures of Re(I) tricarbonyl tropolonato complexes with various monodentate incoming ligands were obtained in the study and will form part of this presentation.
Investigation of metal supported MCF catalysts using PDF technique
Authors: Poulain Agnieszka , Kimber Simon , Sobczak Izabela , Ziółek Maria
Published: November 2015

Functionalisation of silica catalysts (e.g. MCF) supported by anchoring of organosilanes (e.g. aminopropylalkoxysilanes) may change the catalytic properties of the system and also can be used for the further grafting of noble metals [1-2]. In the case of metal loading, in the following calcination process thermal activation and thermal transformation take place leading to the sintering of metal particles, which results in creation of bigger metal crystals. The pair distribution function (PDF) technique is a powerful tool for studying amorphous, crystalline and partially crystalline materials [3]. It bases on model free Fourier transform of X-ray powder diffraction data, and gives the probability of finding any two atoms at a given interatomic distance. A long range order is not necessary and nanostructured materials may be investigated without constraints of conventional crystallographic methods. Structural changes of support (mesoporous cellular foams(MCF))and active sites of new series of metal catalysts (Au, Mo, Nb, Zr) were investigated using PDF technique. All data were collected at ID15 beamline at ESRF: a)catalysts at different steps of synthesis, before and after reactions – measurements in static conditions; b) calcinations processes and in-situ oxidation reactions – measurements at different temperature and with gas flow at ambient pressure. Acknowledgements: National Science Centre in Poland (Project NCN–reg.no.2013/10/ST5/00642) is acknowledged for the partial financial support.
Synthesis & Xray structures of Rare Pentacoordinate Pincer Complexes of Ni(II)
Authors: Mougang-Soume Berline , Zargarian Davit
Published: November 2015

Pincer complexes have been a major focus in organometallic chemistry over the past four decades due to their important potential in catalysis and materials science. In the case of pincer complexes of d8 metals, a growing number of charge-neutral and cationic derivatives featuring hydrides, alkyls, and other reactive moieties have been shown to catalyze important transformations. Regarding the mechanisms of these catalytic reactions, an important issue that remains unresolved concerns the type of intermediates formed upon substrate uptake, namely: A: Do substrates displace one or more hemi-labile donor moieties of the pincer ligand? Or B: Does the substrate occupy a fifth coordination site while the pincer ligand remains intact (Scheme 1)? In this presentation, Xray crystallography is used to describe the influence of the substitue on the 18-electron species based on POCN-Ni precursors. These new diamagnetic complexes are proposed as models for the intermediates that might be involved in catalytic reactions promoted by this family of complexes (Scheme 2).
Structure and Anion Exchangeability of Ni-Al-Type Layered Double Hydroxides
Authors: Moriyoshi Chikako , Hoashi Hirokazu , Sato Hiroaki , Takegawa Masatoshi , Nii Eisaku , Sasai Ryo , Kuroiwa Yoshihiro
Published: November 2015

Layered double hydroxide (LDH) is one of promising inorganic materials for cleaning the environmental water polluted by toxic anions. The crystal structure of LDH is composed of the positively-charged metal hydroxide nanosheets and the anions with water molecules intercalated between the nanosheet layers. To put LDHs for practical use, it is necessary to understand why only special anions can be intercalated into the crystal structure from the aqueous solution. In this study, the anion exchange experiments and the synchrotron radiation x-ray powder diffraction measurements of Ni-Al-type LDHs of several kinds of Ni/Al ratios with chlorine and nitrate anions were performed to investigate the relationship between the anion exchange selectivity and crystal structures. The nitrate ion selectivity is normally poor in most of LDHs with different metal ions in the hydroxide nanosheet [1]. However, the nitrate ions were preferred to the chlorine ions in Ni-Al-type LDH when Ni/Al = 4, whereas the chlorine ions were selected when Ni/Al = 2. The crystal structure analysis revealed that the interlayer distance decreased and the thermal motion of the nitrate ions suppressed in Ni-Al-nitrate-type LDH with increasing the Ni/Al ratio, whereas those of the chlorine ions in Ni-Al-chlorine-type LDH increased and enhanced with increasing the Ni/Al ratio. These results indicate that the nitrate ions are more stable than the chlorine ions in the crystal structure of the Ni-Al-type LDH when the positive charge of the nanosheet is small, i.e. the number of anions is small. The short interlayer distance and the small thermal vibration of anions in the crystal structure are the key to understand the anion selectivity of LDH.
Synthesis, Coordination and Catalytic Tests of New Chiral ferrocenyl P,N ligands
Authors: Wei Muh-Mei , García-Melchor Max , Lledós Agusti , Audin Catherine , Daran Jean-Claude , Poli Rinaldo , Manoury Eric , Deydier Eric
Published: November 2015

Many efforts have been devoted to the development of asymmetric catalysis because of the significant use of chiral compounds as intermediates of pharmaceuticals and advanced materials.[1] Amongst many ligands which have been tested, planar chiral ferrocenes ligands constitutes a privileged family of ligands for enantioselective catalysis.[2] We will disclose in this communication the synthesis of a new chiral N-(p-toluenesulfonyl)-containing ferrocenyl ligands and its coordination chemistry with Ru, Ir and Rh precursors yielding in some cases chiral at metal complexes. [3] Moreover, DFT calculations in order to better understand the nature and stabilities of these complexes will be presented. Additionally, preliminary evaluation of the different complexes as catalysts for the asymmetric transfer hydrogenation of ketones will also be disclosed.
New metal Aryloxide complexes as ceramic precursors and Initiators for ROP
Authors: Chérémond Yvens , Fromm Katharina
Published: November 2015

In addition to the development of new energy-producing processes, finding new energy-saving procedures offers a promising solution to meet our energy needs in the long run. Indeed, cheap organometallic precursors for oxide materials and catalysis are key technologies for energy saving. A wide variety of metal alkoxides/aryloxides[1] has been used not only as precursors for oxide materials, but also as initiators and catalysts for ring-opening polymerization (ROP). Ceramic oxide materials are widely used for many applications, exceptionally in lithium-ion batteries (LIB) material for the last for these recent decades. Also, due to the use of cyclic esters in the tailoring synthesis of biodegradable and bioresorbable materials, interest in the development of well-defined initiators and catalysts has increased. For both cited reasons, iron-based aryloxide complexes offer many advantages, such as the large abundance of iron, their low toxicity and even their biocompatibility[1]. Aryloxide/alkoxide complexes have been also proposed like good route precursors due to their high solubility, low decomposition temperatures, cross linking ability, ease of modification and commercial availability[2].
Molecular trapping by flexible coordination polymers with latent porosity
Authors: Brammer Lee , Vitórica-Yrezábal Iñigo , Wright James , Fletcher Ashleigh
Published: November 2015

Adsorption of gases and vapours, and solid-state reactions, involving crystalline materials are areas of considerable interest. Crystalline materials can thereby be engaged in catalysis, energy storage, separation and sensing applications. The study of such behaviour often requires the application of crystallography combined with other experimental (and computational) methods to obtain a complete understanding. In this presentation, related families of coordination polymers will be discussed. The materials exhibit flexibility in the crystalline state and have been shown to reversibly absorb a variety of small molecules from the vapour phase, including alcohols and arenes, as well as gases.[1,2] The trapped molecules can be located crystallographically within the crystals and have been shown to bind either covalently, through metal-ligand bond insertion reactions, or non-covalently. A series of studies will be described, including reversible single-crystal-to-single-crystal reactions, in situ powder diffraction and spectroscopic studies. The studies involve both laboratory and synchrotron diffraction studies.
From Oxalate-based Heterometallic Compounds to nanocrystalline Ca-Cr Oxides
Authors: Popovic Jasminka , Androš Lidija , Jurić Marijana , Molčanov Krešimir , Planinić Pavica
Published: November 2015

"Metal-organic coordination systems may exert a variety of specific properties including porosity, conductivity, or luminescence and have potential applications in various fields, from heterogeneous catalysis to supramolecular magnetism. Recently, these systems are exploited as molecular precursors by thermal decomposition for the preparation of mixed-metal oxide [1-3]. Since this synthetic route is relatively new and unexplored, there are few reported examples of nanomaterials obtained in this way. The heterobimetallic polymeric compounds [CaCr2(bpy)2(C2O4)4]·0.83H2O}n (1) and {[CaCr2(phen)2(C2O4)4]·0.33H2O}n (2) (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline) were synthesized and characterized. The crystal structure of 2 is reported: the [Cr(phen)(C2O4)2]– unit, through the two oxalate groups, acts as a chelating ligand towards Ca cations, resulting in one-dimensional (1D) double zigzag chains, formed of diamond-shaped units. The ability of compounds 1 and 2 to act as the single-source precursors for the formation of the CaII–CrIII oxides was explored by thermal analysis (TGA and DTA) in the stream of the synthethic air or nitrogen, powder X-ray diffraction and IR spectroscopy. The heat treatment of 1 and 2 resulted in the formation of mixed-metal oxide phases, CaCrO4, α-CaCr2O4 and β-CaCr2O4. Thermal processing of compounds at 11000C in the stream of air, led to the appearance of the orthorhombic β-CaCr2O4 phase as the major crystalline oxide, together with CaCrO4. By heating the samples up to 11000C in nitrogen flow, only β-CaCr2O4 phase was formed, whereas the heating at 14000C caused the crystallization of two polymorphs, α-CaCr2O4 and β-CaCr2O4. J.P. acknowledge financial help from the Croatian Academy of Sciences and Arts. This work has been supported by HAZU grant "XBroad – program za brzo i točno određivanje mikrostrukturnih parametara iz proširenja difrakcijskih linija polikristalnih uzoraka" and ""Nanokristalni oksidi prijelaznih metala: Mikrovalna sinteza i strukturna svojstva"""