New strategies for the<i>ab-initio</i>structure solution in EXPO2005

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Third structure determination by powder diffractometry round robin (SDPDRR-3)

The results from a third structure determination by powder diffractometry (SDPD) round robin are discussed. From the 175 potential participants having downloaded the powder data, nine sent a total of 12 solutions (8 and 4 for samples 1 and 2, respectively, a tetrahydrated calcium tartrate and a lanthanum tungstate). Participants used seven different computer programs for structure solution (ESPOIR, EXPO, FOX, PSSP, SHELXS, SUPERFLIP, and TOPAS), applying Patterson, direct methods, direct space methods, and charge flipping approach. It is concluded that solving a structure from powder data remains a challenge, at least one order of magnitude more difficult than solving a problem with similar complexity from single-crystal data. Nevertheless, a few more steps in the direction of increasing the SDPD rate of success were accomplished since the two previous round robins: this time, not only the computer program developers were successful but also some users. No result was obtained from crystal structure prediction expert

Stereoselective Synthesis of Novel beta,gamma-Epoxyhydroxylamines and 4-Hydroxyalkyl-1,2-Oxazetidines

A simple and efficient stereoselective synthesis of polysubstituted beta,gamma-epoxyhydroxylamines and 4-hydroxyalkyl-1,2-oxazetidines, based on the addition of alpha-lithiated aryloxiranes to nitrones and subsequent cyclization of the corresponding intermediates in a 4-exo-tet mode, is described

Crystal structure of (+)-(2S,3S,1'S)-2-ethyl-N-(1-hydroxymethyl-2-methylpropyl)-2-methyl-3-phenyl-3-phenylamino propanamide, C23H32N2O2

C23H32N2O2, orthorhombic, P212121 (no. 19), a = 6.587 Å, b = 13.118 Å, c = 25.322 Å, V = 2188.0 Å3, Z = 4, Rgt(F) = 0.078, wRref(F2) = 0.217, T = 293 K

Methods of crystallography: powder X-ray diffraction

In the last twenty-five years, relevant theoretical, methodological and experimental advances have been made in the development and application of the X-ray powder diffraction (XRPD) method. In particular, attention has been devoted to the interpretation of XRPD data. The XRPD approach is used currently in mineralogical as well as in many other scientific fields (solid-state chemistry, pharmacology, materials science, etc.) to address a wide range of scientific purposes: qualitative analysis for the identification of the crystalline phases constituting a powder sample; quantitative analysis for estimating the weight fraction of each phase in a mixture; structure solution; microstructural analysis for the inspection of crystalline domain size effects and lattice defects; investigation of highly complex materials: compounds with incommensurate structures, nanoparticles, amorphous materials; studies at non-ambient conditions, in situ, time-resolved and in operando for the description of thermal or compressional behaviour, phase stability and structural evolution. The aim of this chapter is to provide an overview of some basic principles and significant aspects of the XRPD method and examples of its applications to mineralogical problems

Crystal structure of (N-tert-butyl-3,4-diphenyl-1,2-oxazetidin-4-yl)methanol, C19H23NO2

Abstract C19H23NO2, Pbc21 (no. 29), a = 9.481(1) Å, b = 12.073(1) Å, c = 30.079(5) Å, V = 3443.0 Å3, Z = 8, Rgt(F) = 0.077, wRref(F2) = 0.217, T = 293 K.</jats:p