PLAT029_ALERT_3_A_diffrn_measured_fraction_theta_full value Low .      0.896 Why? 

 

PLAT029 Type_3 Check the reported_diffrn_measured_fraction_theta_full

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 Ideally (and a requirementfor publication in Acta Crystallographica),

 this fraction should beclose to 1.0 for theta-full greater or equal  

 to sin(theta/lambda) = 0.6(i.e. 25.24 degrees for MoKa and 67.7 degrees  

 for CuKa  radiation). 

 The three major causes ofincomplete data sets are:

 1 - A missing cusp of datadue to data collection by rotation around  

     the spindle axis only(standard on some image-plate systems). 

     Cure: collect anadditional data set after remounting the crystal.

 2 - The DENZOimageprocessing package has problems with certain strong

     reflections. They areoften excluded from the data set.

     Cure: Add an additionalscan at lower power setting in order to

     include strong loworder reflections. 

 3 - Incomplete scans,possibly based on erroneously assumed higher than

     actual symmetry.  

 Note: The default value of_diffrn_measured_fraction_theta_full that  

 is automatically calculatedand inserted in the CIF by SHELXL-97 might

 generate A-level ALERTSwhen significant numbers of reflections are

 missing at higher thetavalues. In order to avoid such an ALERT,  

 substitute the valuescalculated with the SHELXL instruction 'ACTA 50'

 for _diffrn_reflns_theta_fulland _diffrn_measured_fraction_theta_full

 respectively. ForMo-radiation, corresponding values of 25 degees (or 

 higher) and 0.99 (orhigher) are expected. (See SHELXL manual).

 PLATON may be used toanalyse the case at hand (by invoking either the

 'FCF-VALIDATION' mode orthe 'ASYM-VIEW' mode).