checkCIF procedure

PLAT364

 Large deviations from generally accepted values may indicate model problems,   
 over refinement etc. Default C4-C2 = 1.46 Ang. (X-Ray) value from  
 Ladd & Palmer, Structure Determination by Xray Crystallography (1985). 
 NOTE: C4-C2 indicates a bond between an atom with 4 bonds and one with two
 bonds. Conjugated systems may cause some 'false alarm' messages.