Databases solvated structures

Table 2 Distribution of the 15 Most Abundant Solvents in the Cambridge Crystallographic Database, as the Percentage of Solvate Structures...

One naturally assumes that the larger the database used as a training set, the more reliable will be the calculation for structures not represented therein. But databases reflect what chemists are interested in and what they measure. Thus chemists may over-represent certain structural features (i.e., those which confer desirable properties), and evaluating these by regression analysis may give a skewed perspective of what solvation forces are operating. Examples of this problem appear later. 

A number of statistical analyses of the literature have been carried out in an attempt to estimate the extent of polymorphism. A search of the Cambridge Structural Database on the keywords polymorph , form , modification and phase indicates that about 3.5% of the -350 000 entries fall into this category. Approximately 25 % of the entries are either solvates or hydrates. At the other end of the spectrum, Byrn has reported that of the >150 compounds submitted for crystal form screening and analysis to SSCI, Inc. 85 % exhibit more than one crystal form, 37% are solvates and 31 % are hydrates [40]. Other studies based on different selection criteria reveal results falling somewhere between these two extremes [41]. For instance, Griesser and Burger have collected information on about 600 polymorphic forms and solvates (including hydrates) pharmaceutical compounds that are solid at 25 °C [41c],... 

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