Retrieval of molecular and crystal structures from the CSD

A consideration of the whole bulk of the CSD is both impractical and unnecessary. At the same time, the Cif file format in which the CSD entries are stored requires extensive manipulation of alphabetic data and is impractical for use with computer programs written in the most widely used languages for scientific calculation. For the examples shown in this chapter, some reduced databases have therefore been prepared from the CSD, containing molecular data in numerical form. A full description of the retrieval procedure is given in the Supplementary material (see OPiX manual, Retcif-Coor procedures). 

Some reduced databases have been prepared out of the CSD for use in inter-molecular studies, with renormalized hydrogen positions, and including only crystal structures that pass all the above-described tests. Other general sieves were heaviest element Cl number of C atoms 40 total number of atoms 50 no disorder, no errors, no powder data. X-ray diffraction only, 3D coordinates determined, only organics. Special sieves were used for the different sets, as follows. 

The Z( 1) database only one chemical unit in a crystal (no salts, solvates, molecular complexes, etc.) Z = 1 (one molecule in the asymmetric unit) 35,429 hits, of which 27,535 passed all the tests. 

The Z(l/2) database Z 1, or less than one full molecule in the asymmetric unit (mostly, Z = 1/2) 4,585 hits, 3,468 passing the tests. 

The Z(2) database Z 1, two or more identical molecules in the asymmetric unit 1,501 hits, 825 passing the further tests. 

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