checkCIF procedure

PLAT362

 Large deviations from generally accepted values may indicate model problems,   
 over refinement etc. Default C4-C3 = 1.52 Ang. (X-Ray) value from  
 Ladd & Palmer, Structure Determination by Xray Crystallography (1985). 
 NOTE: C4-C3 indicates a bond between an atom with 4 bonds and one with three
 bonds. Conjugated systems may cause some 'false alarm' messages.