QUALITY CONTROL AND DEPOSITION IN THE CAMBRIDGE STRUCTURAL DATABASE. Sam Motherwell, Cambridge Crystallographic Data Centre, 12 Union Rd., Cambridge, CB2 1EZ. U.K.

All entries in the Cambridge Structural Database are subjected to an extensive sequence of software tests before archiving. The PreQuest program performs two types of checking (a) internal consistency checks e.g. bonds calculated from coordinates versus those given by authors and (b) chemical/crystallographic checks e.g. formulation, abnormal bond lengths, close contacts between molecules. The program is continually being augmented with new tests, e.g. for mis-assigned space groups. 2D chemical diagrams can be input manually or generated automatically from 3D coordinates using geometrical bond-type criteria. PreQuest has been developed to read CIF input data but also reads other established formats such as SHELX.

Modern diffractometry is generating valuable crystal structures by the thousand. It is unlikely that all of these will reach the public domain through formal publication methods, but it is essential that these indispensable data are recorded for future use. The CCDC is already closely involved in journal deposition schemes, and now wishes to extend its coverage to incorporate direct depositions from experimentalists. The PreQuest program will be made available for on-site data validation if required and, after validation at CCDC, authors would receive a CCDC Deposition Number to identify each individual structure. These Numbers could be cited in any subsequent publication. Lists of private communications will be placed in the public domain and individual data sets will be freely available on request.