Validation and checking of crystal structures

Validation and checking of crystal structures

OUTLINE

Valid-ation

• Correct

• Appropriate

• Defensible

Checking is additional to validation

Automated data validation with checkCIF or PLATON

• Checks for

• CIF construction and syntax errors
• missing information
• parameters outside expected norms
• conformation with convention

ALERT LEVELS

Sources of outlier parameters

• Unresolved feature (e.g., untreated disorder)
• Artefact due to limited data quality
• Inadequate procedures (e.g., poor corrections)
• Incorrect structure (e.g., wrong space group)
• A genuinely unusual observation!!

What does validation software do?

When to validate?

• software for data collection, refinement, etc

• - should do its own validation

• use PLATON in final stages of determination

• validate raw CIF from the refinement program

• must validate the final version as well

• avoids problems at submission, refereeing, etc

Looking at the structure

VALIDATION/CHECKING PROCEDURE

Validation and IUCr Journals

Pre-electronic times

Early 1990’s - CIF introduced

Automation of syntax and data checks

Assessment of VRF

How to get a CIF through

What causes most problems?

Common problems ...

Common problems ...

Validation is not a brick wall - either to run into or get over -

Myths and myth-understandings

Myth or not?

checkCIF in 2004

• the new home of checkCIF: http://checkcif.iucr.org

• service sponsored by ACS, CCDC and Elsevier

• an ORTEP plot is now included

• part of new Acta C/E submission procedures

• will soon have online upload of all material for Acta C and E papers (CIF + figures/schemes/structure factors)

Validation and other Journals

Example – an ACS procedure

Other procedures

Example of text

The limits of validation

Possible limits to validation

Error not detectable from CIF data

Other examples

Model complexes for [NiFe] hydrogenase

Lanthanide complexes

Unsuitable SHELX(T)L-97 defaults ?

SUMMARY

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