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

Abstract

The results from a third structure determination by powder diffractometry ͑SDPD͒ 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 tungstate͒. Participants used seven different computer programs for structure solution ͑ESPOIR, EXPO, FOX, PSSP, SHELXS, SUPERFLIP, and TOPAS͒, 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 a͒

Ab initio structure determination of kidney stone potassium quadriurate from synchrotron powder diffraction data, a 150 year problem solved

“…That theory of a double salt, made up of a molecule of uric acid combined with a molecule of an acid urate, was further examined by Kohler [24] who declared that there was no such body as quadriurate. We present here the first recognized crystalline occurrence of a potassium quadriurate as revealed by Structure Determination by Powder Diffractometry (SDPD) methodologies [25]. Being microcrystalline, its crystalline nature may have escaped attention due to the limited means for microscopical observations during the XIX th century where its granular appearance without any obvious crystalline structure led to the conclusion that it was amorphous, or, as stated by Kohler [24], the samples were really just mixtures of urate and uric acid.…”

The charge-flipping algorithm in crystallography

“…Unfortunately, the performance of the modified algorithm is not compared with the standard algorithm without the treatment of the overlapping reflections. The unmodified algorithm was shown to work well several times for powder diffraction data if the structures are not too complex and if the degree of overlap does not exceed the critical limit (Baerlocher, Gramm et al, 2007;Le Bail et al, 2009). It is thus difficult to judge how important the repartitioning scheme employed in this algorithm was for the solution of the examples presented.…”

A new compound in kidney stones? Powder X-ray diffraction study of calcium glycinate trihydrate

“…1) of the sample, and X-ray fluorescence demonstrated the presence of calcium. In the absence of any suitable single crystal, structure determination by powder diffractometry was undertaken following the most modern approaches, as detailed in recent blind tests (Le Bail, Cranswick et al, 2009). Indexing using the McMaille software (Le Bail, 2004) led to a triclinic cell with figures of merit (FoM) M 20 = 70 (de Wolff, 1968) and F 20 = 137 (0.004, 38) (Smith & Snyder, 1979).…”