3/11/2023 0 Comments Singlecrystal 2 cifIn addition, referees are often given only limited access to the supporting experimental data or are simply informed that all crystallographic details have been deposited. The unfortunate current situation is that the number of structures that are submitted for publication each year is orders of magnitude larger than the number of experienced crystallographers and referees knowledgeable in crystallography. Traditionally, this was the responsibility of a professional crystallographer and, when submitted for publication, the referees. A modern PC can easily handle all the necessary calculations.Īn important and certainly final part of a structure determination should be the validation of the structural results. Computing power, being a serious bottleneck in the past, is no longer a limiting factor in this field. ![]() Current CCD (charge-coupled device) detector-based diffractometer systems are capable of producing up to 1000 data sets per year. Much of the data collection, structure solution and refinement steps have been automated and often form part of the software package that comes with the data-collection instrument. Technical advances have turned the structure determination of many crystals of sufficient quality into a routine procedure in the hands of an experienced crystallographer. Parkin (1993 ) addresses in detail the illusive `bond-stretch isomerism' phenomenon. Often, papers include a detailed discussion on an interesting feature of a molecular structure that in hindsight turns out to be based on an artefact. ![]() Some of the more serious errors include incorrectly assigned atom types and missing or too many hydrogen atoms in a structure, obviously with serious implications for the chemistry involved. The assignment of the correct space group to a structure is one of the most common problems, as has been demonstrated many times by Marsh and others ( e.g. An excellent paper by Harlow (1996 ) discusses many examples. Unfortunately, for various reasons, not all structures that end up in the refereed literature and subsequently in databases appear to be correct, either being erroneous only in certain details or containing major errors which lead to the derivation of incorrect conclusions. Structure determinations that are carried out carefully will generally provide incontrovertible results, upon which subsequent research can be built. Much of our current knowledge concerning inorganic and metal-organic compounds is derived from single-crystal studies. Two examples are discussed where proper validation procedures could have avoided the publication of incorrect structures that had serious consequences for the chemistry involved.Ī single-crystal X-ray study has the unique potential to provide `solid' knowledge about the three-dimensional structure of molecules and complexes in the crystalline state along with their intermolecular interactions. PLATON validation can be run at any stage of the structure refinement, independent of the structure determination package used, and is recommended for use as a routine tool during or at least at the completion of every structure determination. ![]() ![]() This paper describes the concepts of validation and the classes of checks that are carried out by the program PLATON as part of the IUCr checkCIF facility. The implementation of validation procedures by other journals is in progress. Validation was pioneered by the IUCr journal Acta Crystallographica Section C and is currently standard procedure for structures submitted for publication in all IUCr journals. The validation software generates a set of ALERTS detailing issues to be addressed by the experimenter, author, referee and publication journal. In this way, many errors in published papers can be avoided. The results of a single-crystal structure determination when in CIF format can now be validated routinely by automatic procedures.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |