Solving crystal structures from powder data. V. Located molecular fragment and powder-pattern decomposition

Abstract

In direct procedures for crystal structure solution from powder data, information on the location and orientation of a molecular fragment may readily become available. Such information may be used retrospectively to improve the powder‐pattern decomposition, with favourable effects on the phasing process. A method is described by which accurate estimation of a large number of structure‐factor moduli is possible by exploiting the prior partial structural information.

Synthesis and Thermal Behavior of Heteroleptic γ‐Substituted Acetylacetonate‐Alkoxides of Titanium

“…[20] The resulting set of hkl was used for structure solution and refinement. The structures were solved by direct methods with SIR97 [21] and the least-square refinement on F2 was achieved with the CRYSTALS software. [22] All non-hydrogen atoms were refined anisotropically.…”

Whole powder pattern decomposition methods and applications: A retrospection

“…or standalone programs ( AJUST by Rius et al , 1996). From the Giacovazzo group in Italy, many improvements were incorporated during the following years in the pattern decomposition Le Bail method: by obtaining information about the possible presence of preferred orientation by the statistical analysis of the normalized structure factor moduli (Altomare et al , 1994); by using the positivity of the Patterson function inside of the decomposition process (Altomare et al , 1998), this having been considered previously (David, 1987; Eastermann et al , 1992; Eastermann and Gramlich, 1993; Easterman and David, 2002); by the characterization of pseudotranslational symmetry used as prior information in the pattern decomposition process (Altomare et al , 1996a); by multiple Le Bail fits with random attribution of intensity to the overlapping reflections, instead of equipartition, followed by application of direct method to large numbers of such data sets (Altomare et al , 2001, 2003, 2004); by the use of a located structure fragment for improving the pattern decomposition process (Altomare et al , 1999b); by the use of probability (triplet-invariant distribution functions) integrated (Carrozzini et al , 1997) with the Le Bail algorithm. The list of structure solutions made from intensities extracted by using the Le Bail method is too long to be given here, but can be found on the Internet (Le Bail, 2005b).…”

Direct methods and the solution of organic structures from powder data

“…In all the cases, both EXPO2004 and EXPO2006 were unable to find the crystal structure. It is worthwhile noting that (a) to check the usefulness of the standard direct methods, we did not use the random decomposition procedure described by Altomare et al (2001), (b) we did not use the recycling technique proposed by Altomare et al (1999) aiming at an improved estimate of the structure factor moduli, via the acquired knowledge of a provisional structure model, and (c) EXPO2004 and EXPO2006 differ in the least-square procedures. Since the EXPO2006 least-squares process plays a CAPTO: (a) the true molecular model; (b) the model arising from the EXPO2006 standard interpretation of the direct-methods map; (c) the model at the end of step (1) of the new procedure; (d ) the molecular model after step (2); (e) the model at the end of step (4); ( f ) the final model (in blue) at the end of the new procedure, superimposed on the true one (in red).…”