Crystallographic Secrets (Easter Eggs)

• The CIF Flack parameter:

  R1: 0.0284 with 0.0565
  wR2: 0.0513 with 0.1337
  Flack: 0.000(4) with 1.1016(4)
   _refine_ls_R_factor_obs+         0.0284
   _refine_ls_wR_factor_obs+        0.0513
   _refine_ls_abs_structure_Flack+  0.000(4)
   _refine_ls_R_factor_obs-         0.0565
   _refine_ls_wR_factor_obs-        0.1337
   _refine_ls_abs_structure_Flack-  1.016(4)
  

• The CIF _chemical_absolute_configuration 'code':
  • rm: co-crystallisation with molecule of known absolute configuration
  • ad: Absolute configuration established by anomalous dispersion effects via e.g. Flack parameter
  • rmad: rm + ad
  • syn: the enantiomer has been assigned by reference to an unchanging chiral centre in the synthetic procedure
  • co: the enantiomer assigned using chiro-optical procedures
  • unk: an arbitrary choice of enantiomer has been made.

• Only ~27% (of 19,455) CIFs declare a value for 'code', of which 2400=ad, 768=rm, 1007=syn.