checkCIF procedure

PLAT369

 Large deviations from generally accepted values may indicate model problems,   
 over refinement etc.  Default C3-C3 = 1.34 Ang. (X-Ray) value from 
 Ladd & Palmer, Structure Determination by Xray Crystallography (1985). 
 NOTE: C3-C3 indicates a bond between atoms with three bonds each. Conjugated
 systems may cause some 'false alarm' messages. A notable exception is the
 C-C bond in -C(=O)-C(=O) systems with an observed mean value of 1.54 Ang.