A Note on the Application of Structural Data in Science and Technology

The development of automated single-crystal and powder diffractometers, sophisticated structure solution programs and fast workstations has in the past two decades, led to a flood of crystallographically characterized materials. Presently, each year many thousands of "small molecule structures" (molecular weights ranging from 100 - 1000) and indexed powder patterns appear in the literature as well as data on several hundreds of macromolecular structures. Searching the primary literature and even the secondary literature, abstracts, reviews etc., poses unsurmountable problems without access to computerized crystallographic databases. Beyond being merely an indispensible source of data on individual structures, the computerized databases have transformed the quantity of data to a new high quality research tool. Search and structure manipulation software enables the chemist to obtain hitherto inaccessible information about relations between crystal structures, molecular reactions, substitution effects and many other chemically relevant phenomena, based on large and statistically significant samples.

Crystallographic databases, or databases on structural data, record not only the relevant bibliographic and chemical information needed to access the original literature, but often also the primary numerical results of the research. Three databases provide comprehensive coverage of atomic coordinate data. Together these databases cover the complete spectrum from metals and alloys, through inorganics, minerals, metal complexes and organometallics, to proteins. Stimulated by advances in network technology, this accumulated information, together with an elaborate library of search and analysis software, is now available at the desktop.

Crystallographic data are widely used in various fields of application, as is illustrated by the following examples.

• Unit cell dimensions are often used to identify a given substance and deviations of lattice parameters of a given substance from standard values can give information on type and amount of incorporation of impurity atoms.
• Full structural data (coordinates and atom types) are used to identy compounds, to predict growth forms and to deduct conformation and chemical reaction pathways.
• Knowledge of the molecular structure helps to understand the nature of drug-receptor interactions.
• New materials with optimum specific properties can be designed by representing all known members of a certain structure type and their properties in a multidimensional diagram and to make a computer draw conclusions with respect to hitherto unknown representatives of this structure type.
• Systematic searches for new superconducting materials in which the arrangement of certain metal atoms favours certain posions, would have been impossible without crystallographic databases.
• Fundamental chemical concepts like atomic radius, bond distance, coordination number and maximum space filling have been tested, proven and improved by the use of databases.
• The structures of the huge number of crystalline phases and molecular compounds that exist and will be synthesized can never be completely analyzed by conventional techniques like X-ray analysis. Therefore structural databases will to some extent replace these techniques and be used for prognoses of unknown structures.

In the SAMSAM project the search facilities of The Cambridge Structural Database with a subset of the data, have been implemented as an introduction to the power of structural database searching techniques for chemical research. The links in the above text can be followed for a more complete description of the other professionally available databases.

Reference: Crystallographic Databases published by the Data Commission of the IUCr. 1987

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