Renewed interest in powder diffraction data indexing

Abstract

Recently released powder indexing programs are reviewed and placed in competition with the established programs (ITO, TREOR, DICVOL, etc.) through a series of problems selected among previously unindexed ICDD entries designated as “high quality”. Benchmarks are provided for testing indexing programs, based on the bethanechol chloride powder diffraction data. Applying these benchmarks leads to a classification (with respect to this specific example) of indexing programs as they face progressively more difficult situations. High data quality and the user experience to obtain it are concluded to remain the best way to indexing success, given that nearly all programs produce excellent results with excellent data. Lack of attention to data quality, even if followed by use of the most efficient programs, will usually lead to failure. It is demonstrated how not restricting oneself to a single indexing program can considerably increase the chances of success.

The determination of crystal structures of active pharmaceutical ingredients from X-ray powder diffraction data: a brief, practical introduction, with fexofenadine hydrochloride as example

“…First, accurate reflection positions must be determined. From these, possible lattice parameters are determined by programs such as ITO,[7] TREOR,[8] DICVOL[9] or McMaille [10,11]. Finally, the user has to judge if the suggested lattice parameters are promising for the investigated compound on basis of criteria such as molecular size, cell volume, crystal system, number of unindexed reflections, etc.…”

Crystal structure and magnetic properties of CuSb2O4

“…A Cu(I) modification with composition Cu 8 Sb 2 O 9 is obtained either by thermal decomposition of CuSb 2 O 6 in an oxygen-free environment, or by a solid state reaction between CuSb 2 O 6 and CuO in air at 1120-1150 °C [9,8]. A cubic Cu(II)-containing phase (Cu 9 Sb 4 O 19 ) also forms at 1100 °C and an oxygen pressure of 10 bar. However, on reheating in air it decomposes above 950 °C to Cu 8 Sb 2 O 9 and CuSb 2 O 6 [9,8].…”

“…A growing demand for structural information on microcrystalline materials is created by the need to characterize naturally occurring micro-minerals, but even more so by the large number of substances synthesized in powder form where growing larger crystals may not be cost effective, or too difficult to achieve. The challenges and limitations, as well as the developments and advances in the methods of structure determination from powder diffraction (SDPD) have been reviewed by numerous authors [16][17][18][19][20]. The determination of crystal structures from powder diffraction data remains a non-trivial process.…”

Direct space methods of structure determination from powder diffraction: principles, guidelines and perspectives

“…This can be a complex and sometimes is the most difficult step for ab-initio structure determination, and is the subject of abundant literature (Bergmann et al, 2004). Practically, tools such as Crysfire (Shirley, 2002) will yield a list of possible unit cells and space groups with a ranking, generally giving few possibilities which can then be used for the algorithm performing the structure search in direct space.…”