Advanced Crystallography: Refinement of Disordered ... - Bruker

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Types of constraints in SHELXL• Constraints for special positions: the necessary constraints on co-ordinates,occupancies and U ij are derived automatically.• Rigid groups (AFIX 6 … AFIX 0): the 3 positional parameters per atom are replaced by3 rotations and 3 translations for the whole rigid group. Atoms may not be in more thanone rigid group.• Riding hydrogen atoms (AFIX mn): x H = x C + ∆x – noextra positional parameters.• Fixed parameters: add 10 to x, y, z, occ, U etc. Typically occupancies are fixed at 1.0by adding 10, i.e. given as 11.0• Free variables: can be used to add extra linear constraints to the usual refinementparameters and also be used instead of restraint target values. This provides aconvenient way of getting target values with esd’s for use as restraints in otherstructures.November 13, 2012 Disorder Webinar14
Special position constraintsExample: Atom on twofold axis in space group C2. The two positions relatedby the twofold axis (x,y,z: -x,y,-z) coincide when x = 0 and z = 0. Since westill wish to sum over all symmetry operators in the structure factor calculation,the occupancy is fixed at 0.5. The probability ellipsoid used to describe theanisotropic motion should not be changed by the 180º rotation.[U 11 , U 22 , U 33 , U 23 , U 13 , U 12 ] ≡ [U 11 , U 22 , U 33 , -U 23 , U 13 , -U 12 ] which is only trueif U 23 = 0 and U 12 = 0. All these constraints are generated automatically bySHELXL for all special positions in all space groups.November 13, 2012 Disorder Webinar15
Page 3 and 4: Charles Campana, Ph.D.Senior Applic
Page 5 and 6: IntroductionModern X-ray crystallog
Page 8 and 9: SHELXTL vs. SHELX*http://shelx.uni-
Page 10 and 11: Objectives of this presentation•
Page 12 and 13: Constraints and Restraints in SHELX
Page 16 and 17: Rigid group constraintsIn SHELXL, r
Page 18 and 19: Free variablesFree variables are an
Page 20 and 21: Graphical Editors for SHELXL/XL fil
Page 22 and 23: DFIX or SADI?The DFIX restraint is
Page 24 and 25: Restraints on ADP'sNovember 13, 201
Page 26 and 27: Use of PART 1, PART 2 and SAMEISORD
Page 28 and 29: The image part with relationship ID
Page 30 and 31: Disorder between Cl and CNovember 1
Page 32 and 33: November 13, 2012Disorder Webinar32
Page 34 and 35: DMSO disordered over three position
Page 36 and 37: Example 1 - Os 3 (CO) 10 (PPh 2 ~PP
Page 42 and 43: Example 1 - Os 3 (CO) 10 (PPh 2 RPP
Page 44 and 45: Example 2 - Urea Host : Guest Compl
Page 52 and 53: Example 3 - Fe 3 (CO) 12 Refinement
Page 54 and 55: Example 3 - Fe 3 (CO) 12 - shelXle
Page 56 and 57: Example 3 - Fe 3 (CO) 12 Bond Lengt
Page 58 and 59: Example 3 - Fe 3 (CO) 12Comparison
Page 60 and 61: Review and Conclusions• Use of te
Page 62 and 63: Available atwww.bruker.com/service/

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