Syntheses and structures of three new lanthanide coordination compounds with dithiocarbamate ligands are reported. The complexes [Ln(Me(2)dtc)(3)(phen)] (Ln = Pr (1), Nd (2) and Gd (3), Me(2)dtc = N,N-dimethyldithiocarbamate and phen = 1,10-phenanthroline) were synthetized by a simple metathesis between lanthanide(III) nitrate and sodium dimethyldithiocarbamate followed by addition of 1,10-phenanthroline without the exclusion of moisture. Single crystal X-ray analysis showed that all three complexes are isostructural, crystallizing in the triclinic space group P (1) over bar. The Ln-S and Ln-N bond lengths decrease in agreement with the decrease in ionic radii across the lanthanide series. Similar structures with Et(2)dtc ligands show no significant effect on the changes of Ln-S bond lengths and also on the S-Ln-S bite angles. The crystal packing of described complexes is formed via pi-pi stacking interactions and C-H center dot center dot center dot S non-covalent contacts.
We summarize exploratory work on multigrain crystallography. The experimental arrangement comprises a monochromatic beam, a fully illuminated sample with up to several hundred grains in transmission geometry on a rotary table and a 2D detector. Novel algorithms are presented for indexing, integration and filtering with emphasis on handling the complications of spot overlap and the need for on-line analysis. The structure solution and refinement steps are performed by conventional single crystal programs. Simulations are used to verify the algorithms and to probe the overall limitations of the methodology in terms of number of grains, size of unit cell and direct space resolution. First experimental results in the fields of chemistry, structural biology and time-resolved studies in photochemistry are presented. As an outlook, the concept of Total Crystallography is introduced, defined as the simultaneous characterization of the 3D atomic, and 3D grain-scale structure of polycrystalline specimens with phases of unknown composition and structure.
Abstract Theory and principles of the three-dimensional pair distribution function analysis of disordered single crystals are introduced. The mathematical framework is presented and the appearance of pair distribution function patterns is discussed on the examples of some basic disorder models. It is further demonstrated how pair distribution function maps are affected by typical experimental problems. Approaches for a better understanding of such effects and strategies for a proper handing of artifacts in diffuse scattering experiments are proposed.
Quantitatively reliable atomic pair distribution functions (PDFs) have been obtained from nanomaterials in a straightforward way from a standard laboratory transmission electron microscope (TEM). The approach looks very promising for making electron derived PDFs (ePDFs) a routine step in the characterization of nanomaterials because of the ubiquity of such TEMs in chemistry and materials laboratories. No special attachments such as energy filters were required on the microscope. The methodology for obtaining the ePDFs is described as well as some opportunities and limitations of the method.
The first attempts at measuring the optical properties of X-rays such as refraction, reflection and diffraction are described. The main ideas forming the basis of Ewald’s thesis in 1912 are then summarized. The first extension of Ewald’s thesis to the X-ray case is the introduction of the reciprocal lattice. In the next step, the principles of the three versions of the dynamical theory of diffraction, by Darwin, Ewald and Laue, are given. It is shown how the comparison of the dynamical and geometrical theories of diffraction led Darwin to propose his extinction theory. The main optical properties of X-ray wavefields at the Bragg incidence are then reviewed: Pendellösung, shift of the Bragg peak, fine structure of Kossel lines, standing waves, anomalous absorption, paths of wavefields inside the crystal, Borrmann fan and double refraction. Lastly, some of the modern applications of the dynamical theory are briefly outlined: X-ray topography, location of adsorbed atoms at crystal surfaces, optical devices for synchrotron radiation and X-ray interferometry.
Routine X-ray single-crystal structure analysis of Na[C6H4ClO3S]center dot H2O resulted in an orthorhombic layer structure with space group Pnma, Z = 4. In this crystal structure the phenyl rings in a single layer are disordered over two mutually perpendicular orientations with occupancies of 0.500(4) each. Structure determination including superstructure reflections and irregular shaped reflections revealed a twinned, ordered, monoclinic structure, P2(1)/c, Z = 8. Here, within a layer the phenyl rings are arranged alternatingly perpendicular. Pair distribution function analysis (PDF) and lattice-energy calculations confirmed this arrangement. Faint diffuse scattering streaks point to a one-dimensional disorder (concerning the layer-stacking sequence). Application of the order-disorder (OD) approach led to three polytype structures with maximum degree of order (MDO); one of them is the experimental monoclinic structure. This structure was found to have the most favourable energy in the lattice-energy minimisations. However, the energy differences between different polytypes with different stacking sequences are rather small. Hence, the lattice-energy minimisations confirmed the monoclinic P2(1)/c structure with stacking disorder.
A combination of neutron total scattering measurement and reverse Monte Carlo (RMC) refinement is applied to the study of apical Cu-O bond distortions in the high-Tc superconductor YBa2Cu3O6.93. We show that the average structure is not consistent with a split-site model for the corresponding Cu and O positions, but that the local structure nevertheless reveals the existence of two separate apical Cu-O bond lengths. Using G(r) data obtained from a variety of Qmax values we show that this result is independent of the data treatment methodology. We also find that the resulting 'short' and 'long' Cu-O bond lengths agree well with the results of previous EXAFS studies. The existence of bimodal apical Cu-O bond distributions in the context of a single-site average structure model is interpreted in terms of correlated displacements of the Cu and O atoms. We find evidence also for the clustering of short apical Cu-O bonds within our RMC configurations.
At present synchrotron and neutron sources are the preferred choice for PDF analysis, but there is clearly an increasing need for a PDF solution based on in-house diffraction equipment. Such a solution, though limited, will benefit areas where quick feedback about the materials properties is important and will allow the routine application of PDF analysis for materials characterization in university laboratories as well as industrial R&D departments.One interesting application is the use of the PDF technique for comparing amorphous pharmaceutical substances [1]. It is worth mentioning that the use of in-house diffraction equipment for PDF analysis has been reported on numerous occasions (see for example [2-4]).This article describes the latest developments of laboratory X-ray equipment for PDF analysis and discusses some results obtained with such equipment. Three examples - C-60, amorphous MoS3 and crystalline CeO2 - were chosen to demonstrate different aspects of PDF data collection optimization.
A novel approach for studying local spin and atomic dynamics in liquids, glasses and crystalline solids with disorder is discussed. In this approach the dynamic structure factor obtained by inelastic neutron or X-ray scattering is Fourier-transformed to real space into the dynamic atomic pair-density function (DPDF). We discuss the nature of the DPDF and show examples of the results obtained by this method. It is demonstrated that the DPDF primarily represents local dynamics, whereas traveling waves contribute only to broadening the peaks. Thus this method complements the conventional analysis of the dynamic structure factor in terms of dispersion relationship of collective dynamics.
The vagaries of recrystallisation are highlighted in this contribution which describes the full characterisation of crystals isolated from the recrystallisation of [Cu2L4(EtOH)(2)] from a 1 : 2 mixture of DMSO and CHCl3 (v/v); L is 4-nitrobenzoate. Slow evaporation over four weeks yielded blue-green crystals of 1 that were shown to be a rare example of a three-component co-crystal comprising [CuL2(OH2)(DMSO)](2), [CuL2(OH2)(2)(DMSO)] and [CuL2(OH2)(DMSO)(2)] in the ratio 1 : 2 : 2. After crystals of 1 were removed from the solution, blue crystals of 2 were isolated after another week had elapsed. These proved to be [CuL2(OH2)(DMSO)(2)] and to be the trans-DMSO isomer of one of the components of 1. The supramolecular aggregation in each crystal structure features ten-membered {center dot center dot center dot HOH center dot center dot center dot OCOCuOCO} synthons whereby the hydrogen atoms of a water molecule link two carbonyl-0 atoms of another complex molecule. In 1, these synthons lead to an isolated six-copper aggregate, and in 2, these lead to supramolecular chains. IR and thermal analysis (TGA and DSC) data are also presented. Crystal data for (1): triclinic, P (1) over bar, a = 13.9035(4), b = 15.5305(4), c = 15.7069(4) angstrom, alpha = 80.062(2), beta = 83.174(2), gamma = 70.109(2)degrees, V = 3134.75(15)angstrom(3), Z = 2, R = 0.036. Crystal data for (2): monoclinic, C2/c, a = 30.0180(16), b = 5.8440(3), c = 14.2639(8) angstrom, beta = 114.669(7)degrees, V = 2273.9(2) angstrom(3), Z = 4, R = 0.027.
Abstract Resonant X-ray diffraction and differential atomic pair distribution functions method is illustrated with results from a study of 4.5(3) nm Pt, Au and Pt0.51Au0.49 particles. By doing experiments at two energies close to the K absorption edge of Pt the atomic correlations relative to Pt and Au atoms in the alloy particles are differentiated. The experimental data show that Pt and Au atoms in all three samples arrange in a face centered cubic type structure while keeping their bond lengths of 2.76 Å and 2.86 Å, respectively, virtually unchanged. This leads to increased local structural distortions in the alloyed Pt0.51Au0.49 particles that may affect their catalitic properties substantially.
Mg2Co- and MgCo2-like local atomic arrangements in mechanically alloyed MgxCo100-x were investigated using atomic pair distribution function (PDF) analysis derived from synchrotron X-ray total scattering data. We show that changes in MgxCo100-x PDFs with x are well explained by the structural features of Mg2Co and MgCo2. This strongly supports our two-phase model picture where Mg2Co-like phase continuously increases while MgCo2 decreases with increasing Mg content in MgxCo100-x
A combination of X-ray and neutron PDF measurements with powder diffraction and EXAFS data was used to determine the structures of a V-Mo-Nb-oxide catalyst and its poorly crystallized precursors that exhibit the strongest catalytic activities. The crystalline material belongs to space group P (4) over bar2(1)m, a = 22.8, c = 4.002, and is build up of pentagonal MeO7 bipyramids surrounded by edge sharing Me-octahedrons (Me = Mo, V, Nb). In the average structure all MeO7 units are at the same z-level, while the local structure analysis shows systematic shifts along [001]. Samples synthesized at 300 degrees C and 400 degrees C exhibit a nanostructure, whose local structure predates the final crystalline structure. Initial nanoparticles are spherical and grow predominantly along the c-axis. The successful analysis required a reverse analysis that took the crystalline material as starting model for the samples synthesized at lower temperatures.
This paper focuses on statistical methods and formulas that solve the constraints (R) over cap (2)(q)(x(1), ..., x(N)) = R-q(2) for all q. To this end we invented several non trivial techniques. We introduce a functional measure that uses the Patterson function and show that this functional measure is equivalent to using a non uniform prior distribution of the x(i) given by a product of delta functions delta((R) over cap (2)(q)(x(1) ,..., x(N)) - R-q(2)). We then use a representation of the delta function for calculating probabilities. In this paper we don't aim to give a "final" formula (this we hope to do in a future paper) but we emphasize instead on the method. We also show in this paper that SAD gives almost the same conditional j.p.d. of the phases given the magnitudes of the structure factors. Finally we show that by using plausible prior densities of the x(i) the principal part of the probabilities of phases given some neighborhood does not depend anymore on the number of atoms which is a completely new and unexpected result. The Bessel functions will play a dominant role in all our formulas.
Abstract The new cyclotriphosphate Mg(NH4)4(P3O9)2 · 4 H2O was synthesized by the metathesis reaction of Boullé and characterized by single crystal X-ray diffraction and infrared spectroscopy. The compound crystallizes in the monoclinic system, space group P21/c, with the following unit cell parameters: a = 8.6120(5), b = 14.6390(10), and c = 8.8610(17) Å; β = 95.330(8)°; V = 1112.3(2) Å3. The crystal structure was refined up to a final R value of 0.0277 using 2543 independent reflections. Magnesium cation is coordinated by two P3O9 3– ring anions and four water molecules, displaying quite regular octahedral geometry. Ammonium polyhedra NH41O6 and NH42O6 are, respectively, connected to the MgO6 octahedron by O10—O4 edge and the O11 water molecule. The three-dimensional framework is built up from [Mg(P3O9)2(H2O)4]4– complex anions linked together via hydrogen bonds interactions made up by (NH4)+ cations. Last, the infrared spectrum of title compound was recorded and interpreted.
Co-crystals formed between anthranilic acid and each of 4,4'-bipyridine (1), 1,2-trans-1,2-bis(4-pyridyl)ethene (2) and 1,2-bis(4-pyridyl)ethane (3) have been formed from solutions containing 2: 1 stoichiometric quantities of the reagents. Each structure features a centrosymmetric three-molecule aggregate mediated by O-H center dot center dot center dot N(pyridyl) hydrogen bonds indicating the robustness of the seven-membered {center dot center dot center dot HOCO center dot center dot center dot HCN} heterosynthon. The structures of (1)-(3) are isomorphous whereby the three-molecule aggregates are connected into flattened helical chains by amino-N-H center dot center dot center dot O(carbonyl) hydrogen bonds; the chains are consolidated into the three-dimensional structure by pi center dot center dot center dot pi interactions. The magnitude of the O-H center dot center dot center dot N hydrogen bonds in (1)-(3) are correlated with the basicity of the pyridine residue.
Crystals of Zn(NO3)(2)center dot H2O and Mn(NO3)(2)center dot H2O were synthesized by heating melts of the respective penta- or hexahydrates. Single crystal X-ray diffraction of the two highly hygroscopic phases reveals new sheet-structure types: Zn(NO3)(2) H2O [Pbca, a = 9.722(1), b = 5.865(1), c = 17.799(2) angstrom (120 K), Z = 8, R-1 = 0.025]; Mn(NO3)(2)center dot 2 H2O [P2(1)2(1)2(1), a = 5.921(1), b = 8.835(1), c = 22.882(2) angstrom (120 K), Z = 8, R-1 = 0.020]. Zn(NO3)(2)center dot H2O is built of only one kind of complicated, corrugated sheets held together by hydrogen bonds, while Mn(NO3)(2)center dot 2 H2O is built of alternating sheets with Mn in 6- and 7-fold coordination, respectively, again interconnected by hydrogen bonds. While in Zn(NO3)(2)center dot H2O the hydrogen bond system is quite clear-cut, this is not the case in Mn(NO3)(2)center dot 2 H2O. Contrary to expectation, the thermal expansion is not clearly largest perpendicular to the sheets in both compounds.In the well known structures of the nitrate dihydrates of Mg, Co and Ni new refinements allowed to locate the hydrogen atoms.Together with Mn(H) nitrate monohydrate and the dihydrates of Mg, Co, Ni, Zn and Cd the two new nitrates form an interesting group of sheet structures.
