Analysis of accurate experimental and theoretical structure factors of diamond and silicon reveals that the contraction of the core shell due to covalent bond formation causes significant perturbations of the total charge density that cannot be ignored in precise charge density studies. We outline that the nature and origin of core contraction/expansion and core polarization phenomena can be analyzed by experimental studies employing an extended Hansen-Coppens multipolar model. Omission or insufficient treatment of these subatomic charge density phenomena might yield erroneous thermal displacement parameters and high residual densities in multipolar refinements. Our detailed studies therefore suggest that the refinement of contraction/expansion and population parameters of all atomic shells is essential to the precise reconstruction of electron density distributions by a multipolar model. Furthermore, our results imply that also the polarization of the inner shells needs to be adopted, especially in cases where second row or even heavier elements are involved in covalent bonding. These theoretical studies are supported by direct multipolar refinements of X-ray powder diffraction data of diamond obtained from a third-generation synchrotron-radiation source (SPring-8, BL02B2).

The iron(III) complexes of tetra amidato macrocyclic ligands (TAMLs) ([Fe{1-X1-2-X2C6H2-4,5-(NCOCMe2NCO)2CR2}(OH2)]- , 1: X1 = X2 = H, R2 = Me2 (a), R2 = (CH2)2 (b); X1 = X2 = Cl, R2 = F2 (c), etc.), which the proton is known to demetalate at pH < 3, are also subject to catalyzed demetalation by Brønsted acid buffer components at pH 4-9 such as H2PO4-, HSO3-, and CH3CO2H, HO2CCH2CO2-. Buffers based on pyridine (py) and tris(hydroxymethyl)aminomethane (TRIS) are catalytically inactive. Where reactions proceed, the products are demetalated TAMLs and iron species of variable composition. Pseudo-first-order rate constants for the demetalation (kobs) are linear functions of the acid concentrations, and the effective second-order rate constants k1,eff have a hyperbolic dependence on [H+] (k1,eff = a1[H+]/(b1+[H+]). The rate of demetalation of 1a in H2PO4-/HPO42- buffer is appreciable, but the kobs values for 1b and 1c are immeasurably low, showing that the rates are strongly affected by the CR2 or "tail" fragments, which are known to potently affect the TAML basicity. The reactivities of 1 depend insignificantly on the aromatic ring or "head" group of 1. The proposed mechanism involves precoordination of the acidic buffer species followed by hydrolysis. The demetalating abilities of buffer species depend on their structures and acidities. Thus, although pyridine-2-carboxylic (picolinic) acid catalyzes the demetalation, its 3- and 4-isomers (nicotinic and isonicotininc acids) are inactive. The difference is rationalized to result from the ability that only coordinated picolinic acid has to deliver a proton to an amidato nitrogen in an intramolecular manner. The reaction order in picolinic acid equals one for 1a and two for 1b. For 1b, "inactive" pyridine and nicotinic acid speed up the demetalation in the presence of picolinic acid, suggesting that the second order arises from the axial binding of two pyridine molecules, one of which must be picolinic acid. The binding of pyridine- and imidazole-type ligands was confirmed by UV/vis equilibrium measurements and X-ray crystallography. The implications of these mechanistic findings for designing superior Fe-TAML oxidation catalysts and catalyst formulations are discussed using the results of DFT calculations.

No abstract

Single‐phase samples of the compounds K8Al8Si38 (1), Rb8Al8Si38 (2), and Cs7.9Al7.9Si38.1 (3) were obtained with high crystallinity and in good quantities by using a novel flux method with two different flux materials, such as Al and the respective alkali‐metal halide salt (KBr, RbCl, and CsCl). This approach facilitates the removal of the product mixture from the container and also allows convenient extraction of the flux media due to the good solubility of the halide salts in water. The products were analyzed by means of single‐crystal X‐ray structure determination, powder X‐ray and neutron diffraction experiments, 27Al‐MAS NMR spectroscopy measurements, quantum chemical calculations, as well as magnetic and transport measurements (thermal conductivity, electrical resistivity, and Seebeck coefficient). Due to the excellent quality of the neutron diffraction data, the difference between the nuclear scattering factors of silicon and aluminum atoms was sufficient to refine their mixed occupancy at specific sites. The role of variable‐range hopping for the interpretation of the resistivity and the Seebeck coefficient is discussed.

Alkylammonium lead(ii) iodide materials (APbI3), based on the general formula of CH3-(CH2)n-NH3PbI3, may lead to a monumental leap in developing affordable photovoltaics. Herein, we correlate the structure and function relationships of alkylammonium lead(ii) iodide in solar cells.

An improved technique to study transferred lipid monolayers by electron microscopy and electron diffraction is presented. In combination with a microfluorescence technique it provides a powerful technique to study the microstructure of monolayers. It is demonstrated that the non-horizontal slope of the isotherms at the fluid-to-crystalline phase transition is due to the coexistence of fluid and crystalline phases up to the second order like transition to the completely condensed crystalline state. An electrostatic model is presented which explains (1) the thermodynamic stability of the fluid-solid coexistence, (2) the non-horizontal slope of the transition region, (3) the existence of a pressure dependent but uniform size of the crystalline platelets at the initial slope of the transition region

The intermetallic compound ZnSb is an interesting thermoelectric material, largely due to its low lattice thermal conductivity. The origin of the low thermal conductivity has so far been speculative. Using multi-temperature single crystal X-ray diffraction (9 -400 K) and powder X-ray diffraction (300 -725 K) measurements we characterized the volume expansion and the evolution of structural properties with temperature and identify an increasingly anharmonic behavior of the Zn atoms. From a combination of Raman spectroscopy and first principles calculations of phonons we consolidate the presence of low-energy optic modes with wavenumbers below 60 cm -1 . Heat capacity measurements between 2 and 400 K can be well described by a Debye-Einstein model containing one Debye and two Einstein contributions with temperatures Θ D = 195K, Θ E1 = 78 K and Θ E2 = 277 K as well as a significant contribution due to anharmonicity above 150 K. The presence of a multitude of weakly dispersed low-energy optical modes (which couple with the acoustic, heat carrying phonons) combined with anharmonic thermal behavior provides an effective mechanism for low lattice thermal conductivity. The peculiar vibrational properties of ZnSb are attributed to its chemical bonding properties which are characterized by multicenter bonded structural entities. We argue that the proposed mechanism to explain the low lattice thermal conductivity of ZnSb might also control the thermoelectric properties of other electron poor semiconductors, such as Zn 4 Sb 3 , CdSb, Cd 4 Sb 3 , Cd 13-x In y Zn 10 , and Zn 5 Sb 4 In 2-δ .2

In industrial settings, X-ray computed tomography scans are a common tool for inspection of objects. Often the object can not be imaged using standard circular or helical trajectories because of constraints in space or time. Compared to medical applications the variance in size and materials is much larger. Adapting the acquisition trajectory to the object is beneficial and sometimes inevitable. There are currently no sophisticated methods for this adoption. Typically the operator places the object according to his best knowledge. We propose a detectability index based optimization algorithm which determines the scan trajectory on the basis of a CAD-model of the object. The detectability index is computed solely from simulated projections for multiple user defined features. By adapting the features the algorithm is adapted to different imaging tasks. Performance of simulated and measured data was qualitatively and quantitatively assessed.The results illustrate that our algorithm not only allows more accurate detection of features, but also delivers images with high overall quality in comparison to standard trajectory reconstructions. This work enables to reduce the number of projections and in consequence scan time by introducing an optimization algorithm to compose an object specific trajectory.X-ray Computed Tomography (CT) is a widely used tool for inspection in industrial settings, in particular for nondestructive testing (NDT). It is used, for example, for dimensional metrology and defect detection. Apart from the non-existing radiation exposure issue, CT in NDT has several differences when compared to medical CT, such as large variations in object-size and attenuation. One common major issue is the importance of reduced scan times. This facilitates the expansion of industrial CT application from the laboratory to the factory with a full test coverage in the production line.Currently, industrial CT almost exclusively uses standard circular or helical trajectories in combination with filtered backprojection (FBP) reconstruction algorithms. The increased availability of high performance computing hardware, for example GPUs 1,2 , facilitates the revival of iterative reconstruction algorithms, which inherently support arbitrary trajectories. To exploit the flexibility of iterative reconstruction methods, it makes sense to move towards trajectories that include "valuable" acquisition poses (position and orientation of the source/detector arrangement, often also called projections) and exclude "less valuable" acquisition poses. In Varga et al. 3 it was demonstrated that not all acquisition poses have the same value for the reconstructed image. For example, for reconstruction of an edge at least one X-ray has to be tangential to the edge 4 . Furthermore, image quality can be severely reduced by artifacts due to beam-hardening and high attenuation materials. Typically it is not possible to avoid such artifacts completely, but one can choose a trajectory in such a way that the region of interest is not (or less) aff...