Increasing data completeness in synchrotron tts-microdiffraction experiments for δ-recycling phasing of low-symmetry compounds

CRESPI, ANNA; RIUS, JORDI; COLOMBO, FERNANDO; VALLCORBA, ORIOL

Zeitschrift für Kristallographie - Crystalline Materials

de Gruyter

Lugar: Berlín; Año: 2017 vol. 0 p. 1 - 8

2194-4946

Successful phasing of synchrotron through-the-substratemicrodiffraction data by δ-recycling direct methodslargely depends on the number of missingintensities caused by the limited sample rotation range [J.Rius, Direct phasing from Patterson syntheses by δ recycling.Acta Cryst. A 2012, 68, 77?81]. Particularly, for theunfavorable triclinic system, dataset completeness resultingfrom a single series of consecutive φ-scans coveringa total φ interval of ±35° is around 41%. This value is notenough for the routinary solution of a crystal structure byδ-recycling but can be increased by ~29% by applying theorthogonal χ strategy consisting of merging the informationof two series of orthogonal φ-scans collected at thesame microvolume of the polished thin section. Test calculationsusing simulated and experimental tts-data ofthe triclinic mineral axinite confirm that, with the helpof the orthogonal χ strategy, crystal structures can besolved routinely. Since data in the ±35 φ-interval are normallyaccessible even for relatively thick glass-substrates(1?1.5 mm), a crystal structure can be determined from asingle microvolume. For high-symmetry phases, due tothe Laue symmetry redundancy, a single series of φ-scansnormally suffices for the application of δ-recycling. However,when for experimental causes this series is incomplete,the orthogonal χ strategy also provides a simpleway to increase the completeness which besides allowingsolving the structure, is also beneficial for the subsequentrefinement.