Bruker AXS Visualize Select Create Application Note SCD 375 Pseudo Merohedral Twinning: How to Treat a Six-fold Twin In dealing with pseudo-merohedral twins, cell refinement and data integration need special care due to the presence of closely overlapping spots. Careful selection of trusted areas in which to refine the cell will improve the reliability of the cell parameters. One of the pitfalls during integration of data from pseudo-merohedral twins is that the spot shape changes continuousl
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  In dealing with pseudo-merohedral twins, cell reinementand data integration need special care due to the presenceo closely overlapping spots. Careul selection o trustedareas in which to reine the cell will improve the reliability othe cell parameters.One o the pitalls during integration o data rompseudo-merohedral twins is that the spot shape changescontinuously due to the systematic overlap o areas oadjacent spots. The approach described here can beused or all multi-domain pseudo-merohedral cases. It isillustrated using a six-old twin that shows a reversibletransition rom triclinic cells to single crystal state with ahexagonal cell. Indexing and Domain Orientation The initial indexing result is severally biased towardsthe overlap position, resembling hexagonal setting. Byvisualizing the peaks in 3D space, ‘trusted’ areas can beidentiied. The pseudo precession pictures will help identiyin which planes spots can be separated.It is also apparent that the spot positions o the tricliniccell at low temperature have inherited the hexagonalarrangement rom the room temperature cell. This relationwas conirmed by CELL_NOW 2 .The hk0 plane only contains exactly overlaid peak positionsand should be included in the cell reinement. Planesrom hk1 to hk5 were excluded due to the presence osystematically partial overlapping peaks. The higher orderhk-planes have separated spots. The reversible (triclinic/ hexagonal) cell properties o this sample avors the use ogenerated cells derived rom one well-reined domain. BrukerAXS VisualizeSelectCreateIntegrateScale andCorrectSolve andRefne Application Note SCD 375 Pseudo Merohedral Twinning:How to Treat a Six-fold Twin   Steps and Tools ã Harvest spots rom all rames (~10.000 spots.)ã Index on low resolution data.ã Lattice Overlay to isolate one domain.ã Select area to remove overlapping peaks.ã Refne cell o domain 1 against the selected peaks.ã Transorm unit cell to create 5 remaining cells byrotating multiples o 60 degrees around the c-axis.ã Integrate the images with all 6 cells.ã Scale and correct or absorption using TWINABS 1 .ã Solve the structure rom the HKLF4 data.ã Refne the structure against the HKLF5 data.  All configurations and specifications are subject to change without notice. Order No. A86-EXS002 © 2007 Bruker AXS Inc.Printed in the United States of America. Any trademarks are the property of the respective owners. Data Collection Measurements were done using Cu radiation. Datacollection with 0.5 degrees images rom 10 to 30 secondsper image. Detector distance 50 mm. Integration All six domains were integrated concurrently using SAINT 3 .The cells were not reined to avoid reining on peaksaected by overlap. Results The structure behaves well in unconstrained reinementusing the HKLF5 data. The reely reined batch actors oreach domain range rom 0.154 to 0.191. Refinement results (shelxl-97 4 ): R1=0.0673, 24906 Fo>4sig(Fo)R1=0.0754 or all 29361 datawR2 = 0.2402,Restrained GooF= 1.032 all data< σ (bond)> = 0.0026 Conclusions ã Visual representation and interactive tools to selectreliable peaks are essential.ã Absorption correction and scaling can be successullyapplied through TWINABS.ã Generating idealized classical twin cells by pseudosymmetry operations, provides an excellent descriptiono the spot positionsã All operations are possible through the APEX2 graphicaluser interace (version2.2). References 1 Sheldrick, G.M. (2002). TWINABS, Bruker AXS, Madison.2 Sheldrick, G.M. (2003). CELL_NOW, Bruker AXS, Madison.3 Bruker (2001). SAINT, Bruker AXS, Madison.4 Sheldrick, G.M. (1997). SHELXL-97, Uni. Göttingen.Thanks to R. Pietschnig or providing the crystal. Authors Leo Straver and Rob HootBruker AXS, Oostsingel 209, 2612HL Delt,The Netherlands BrukerAXSInc. Madison, WI, USAPhone +1 (800) 234-XRAYPhone +1 (608) 276-3000Fax +1 (608) 276-3006in   BrukerAXSGmbH Karlsruhe, GermanyPhone +49 (721) 5   95-28   88Fax +49 (721) 5   95-45   87in BrukerAXSBV Delt, The NetherlandsPhone +31 (15) 215 2400Fax +31 (15) 215 2599in Figure 1: Visual representation and selection tools 6-old spot3D lattice viewLattice overlayselection toolThe hk8 precession planeRefnementresult using alldomains
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