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The title compound, [Fe2(C5H5)2(C40H22O2)] or 1,4-(FcPh)2Aq [where FcPh is 2-(4-ferrocenylphenyl)ethynyl and Aq is anthraquinone], was synthesized in an attempt to obtain a new solvent-incorporating porous material with a large void space. Thermodynamic data for 1,4-(FcPh)2Aq show a phase transition at approximately 430 K. The crystal structure of solvent-free 1,4-(FcPh)2Aq was determined at temperatures of 90, 300 and 500 K using synchrotron powder diffraction data. A direct-space method using a genetic algorithm was employed for structure solution. Charge densities calculated from observed structure factors by the maximum entropy method were employed for model improvement. The final models were obtained through multistage Rietveld refinements. In both phases, the structures of which differ only subtly, the planar Aq fragments are stacked alternately in opposite orientations, forming a one-dimensional column. The FcPh arms lie between the stacks and fill the remaining space, leaving no voids. C-H...π interactions between the Ph and Fc fragments mediate crystal packing and stabilization. [ABSTRACT FROM AUTHOR]

An algorithm for determining the element-selective charge density has been developed using the maximum entropy method (MEM), Rietveld analysis and synchrotron X-ray multi-wavelength anomalous powder diffraction data. This article describes in detail both experimental and analytical aspects of the developed method. A structural study of yttrium mono-metallofullerene, Y@C82, 1:1 co-crystallized with toluene using the present technique is reported in order to demonstrate the applicability of the method even when only medium resolution data are available ( d > 1.32 Å). Element-selective MEM charge density maps, computed from synchrotron X-ray powder diffraction data collected at three distinct wavelengths around the yttrium K-absorption edge (∼0.727 A), are employed for determining three crystallographic sites of the disordered yttrium. [ABSTRACT FROM AUTHOR]

The structure of a pharmaceutical compound, prednisolone succinate, has been determined by a newly developed analytical method for ab initio structure determination and refinements from X-ray powder data. It consists of a genetic algorithm (GA) for the structure determination process and the maximum entropy method (MEM), including its variations, for the structure refinement process. The crystal structure of prednisolone succinate has two molecules in the asymmetric unit and the total number of degrees of freedom is 25. in the structure refinement process, the various kinds of MEM analyses, such as difference MEM and omit MEM, in addition to ordinary MEM, play crucial roles in obtaining a better structural model. The data used in the present study were collected at BLO2B2, SPring-8, which allowed the use of a wide d-spacing range, d> 1.0 A. The reliability factors, ~ and R1, of the final structure analysis by Rietveld refinement are less than 0.013 and 0.048, respectively. The structure determined in the present study gives no CHECKCIF alert relating to the fundamental structure, such as interatomic distances and bond angles, even in chemical bonds involving H atoms. [ABSTRACT FROM AUTHOR]

Accurate structure factors of silicon and diamond have been experimentally determined from powder diffraction data measured at the third-generation synchrotron-radiation source SPring-8, BL02B2. The accuracy of the obtained structure factors has been evaluated by comparing with structure factors in the literature measured by the Pendellösung method and with some from theoretical calculations. The results indicate that the structure factors from powder data are accurate enough to discuss the experimental charge-density distributions of these materials. The number of structure factors of silicon determined in the present study is 104, which is three times more than that of previous Pendellösung data. The experimental charge densities have been obtained by the maximum-entropy method from the present structure factors. The charge densities at bond mid-points for silicon and diamond show good agreement with different kinds of theoretical calculations. The present study proved that the powder diffraction at SPring-8 is a promising method for determination of experimental charge density for a wider range of materials. [ABSTRACT FROM AUTHOR]

Crystal structure determination and analysis have been carried out for the two spin-crossover compounds [Fe(teeX)6](BF4)2 (teeX is haloethyltetrazole; X = I: teei; X = Br: teeb), in both their high-spin (near 300 K) and their low-spin states (T = 90 K), using high-resolution powder-diffraction data collected at the ESRF (Grenoble, France) and SPring8 (Japan) synchrotron radiation facilities. The structures of teei have been solved using various direct-space structure determination techniques (grid search, genetic algorithm and parallel tempering) and refined with the Rietveld method using geometrical restraints. In the case of teeb, a structural model was found but a full refinement was not successful because of the presence of a significant amount of an amorphous component. Analysis of the structures (space group P21/c, Z = 2) and diffraction data, and the absence of phase transitions, show the overall structural similarity of these compounds and lead to the conclusion that the gradual spin-crossovers are likely to be accompanied by small structural changes only. [ABSTRACT FROM AUTHOR]

Examines the application of the Electron and Nuclear Image Generator by Max-ent Analysis (ENIGMA) for huge protein and polymer systems. Use of ENIGMA in evaluating three-dimensional electron and nuclear density from X-ray and neutron diffraction data; Minimization of computing time and memory space; Compatibility of the package to various parallel computers.

In the title compound, [Fe(C5H5)(C27H16NO)], designed and synthesized to explore a new electron-donor (D) and -acceptor (A) conjugated complex, the two cyclo-penta-dienyl rings adopt an eclipsed conformation. The anthracene tricycle is distorted towards a butterfly conformation and the mean planes of the outer benzene rings are inclined each to other at 22.7 (3)°. In the crystal, mol-ecules are paired into inversion dimers via π-π inter-actions. Weak inter-molecular C-H⋯π inter-actions link further these dimers into one-dimensional columns along the b axis, with the ferrocenylethynyl arms arranged between the stacks to fill the voids.

Accurate structural refinement of a putative acylphosphatase using 1.3 A X-ray diffraction data was carried out using charge densities determined by the maximum-entropy method (MEM). The MEM charge density clearly revealed detailed features of the solvent region of the putative acylphosphatase crystalline structure, some of which had never been observed in conventional Fourier maps. The structural model in the solvent region was constructed as distributions of anisotropic water atoms. The omit-difference MEM maps and the difference MEM maps were effective in revealing details of the protein structure, such as multiple conformations of the side chains of amino-acid residues, anisotropy of atoms and H atoms. By model building using the MEM charge densities, the reliability factors R1 and R free in the SHELX refinement were dramatically improved from 17.9% and 18.3% to 9.6% and 10.0%, respectively. The present results prove the usefulness of MEM in improving the accuracy of refinement of protein crystal structures.

Crystal structure determination and analysis have been carried out for the two spin-crossover compounds [Fe(teeX)(6)](BF(4))(2) (teeX is haloethyltetrazole; X = I: teei; X = Br: teeb), in both their high-spin (near 300 K) and their low-spin states (T = 90 K), using high-resolution powder-diffraction data collected at the ESRF (Grenoble, France) and SPring8 (Japan) synchrotron radiation facilities. The structures of teei have been solved using various direct-space structure determination techniques (grid search, genetic algorithm and parallel tempering) and refined with the Rietveld method using geometrical restraints. In the case of teeb, a structural model was found but a full refinement was not successful because of the presence of a significant amount of an amorphous component. Analysis of the structures (space group P2(1)/c, Z = 2) and diffraction data, and the absence of phase transitions, show the overall structural similarity of these compounds and lead to the conclusion that the gradual spin-crossovers are likely to be accompanied by small structural changes only.