PowderSolve– a complete package for crystal structure solution from powder diffraction patterns

Abstract

Powder diffraction techniques are becoming increasingly popular as tools for the determination of crystal structures. The authors of this paper have developed a software package, named PowderSolve, to solve crystal structures from experimental powder diffraction patterns and have applied this package to solve the crystal structures of organic compounds with up to 18 variable degrees of freedom (de®ned in terms of the positions, orientations, and internal torsions of the molecular fragments in the asymmetric unit). The package employs a combination of simulated annealing and rigid-body Rietveld re®nement techniques to maximize the agreement between calculated and experimental powder diffraction patterns. The agreement is measured by a full-pro®le comparison (using the R factor R wp ). As an additional check at the end of the structure solution process, accurate force-®eld energies may be used to con®rm the stability of the proposed structure solutions. To generate the calculated powder diffraction pattern, lattice parameters, peak shape parameters and background parameters must be determined accurately before proceeding with the structure solution calculations. For this purpose, a novel variant of the Pawley algorithm is proposed, which avoids the instabilities of the original Pawley method. The successful application and performance of PowderSolve for crystal structure solution of 14 organic compounds of differing complexity are discussed.

X-ray Structural Investigation of Nonsymmetrically and Symmetrically Alkylated [1]Benzothieno[3,2-b]benzothiophene Derivatives in Bulk and Thin Films

“…43 Crystal structure determination was achieved using a rigid body simulated annealing procedure using PowderSolve program. 44 The geometry of the starting C 8 −BTBT molecule was optimized using DREIDING force field. 45 Moreover, the dihedral angle around the C−C bond connecting the octyl chain to the BTBT core was allowed to vary in the simulated annealing procedure (together with the three translations and three rotations of the rigid geometry optimized C 8 −BTBT molecule) as it is observed in the crystal structure of dialkylated BTBTs that the planes containing the zigzag of the alkyl chains and the plane of the BTBT moiety are not parallel.…”

Docetaxel : Solid state characterization by X-ray powder diffraction and thermogravimetry

“…The unit cell parameters (at room temperature) are : Based on the molecular geometry obtained from the structure of the mixed solvate [3], the structure was solved (29 degrees of freedom) using an ab initio direct space approach. The method is based on a simulated annealing algorithm (Powdersolve [6]). Rietveld refinement (Powder Refinement in the Materials studion application) completed the solution.…”

Polymorphism and hydration of zopiclone : Determination of crystal structures, and thermodynamic studies as a function of temperature and water vapor pressure

“…To minimise preferred orientation effects, a transmission diagram was recorded using a rotating capillary. Based on the molecular structure, unit cell indexing and space group determination, the solution in direct space has been determined using aMonte Carlo Simulated Annealing (MCSA) algorithm (Powdersolve programme [4]). The solution was refined by the Rietveld method using a rigid body approach.…”