At the origin was a series of samples to be checked by X-ray diffraction, they were said to be thalidomide. The analysis revealed that the samples could contain a mixture of the two thalidomide polymorphs (alpha and beta). This could not be concluded from the PDF since it contains data (quite old) for only one polymorph (named alpha variety today). The study could be completed from CSD data. A quantitative analysis procedure by the Rietveld method was established then, for the characterization of these samples (no refinement of atomic coordinates). A pattern showing a 50-50% mixture of polymorphs was selected for the SMRR. A search-match applied on it was concluding, giving the PDF thalidomide (19-1946) in first position by selecting the organic subset.
Problems on the pattern :
The sample-3 pattern presents a zeroshif which does not preclude identification.
Of course, the PDF does not contain the beta-thalidomide, so that, a full correct explanation of the pattern is impossible. No doubt that the search-match program user decision, and experience, can play here enormously for the selection of the final propositions at step 1. Possibly, according to the bad fit, the user may even reject the true thalidomide answer. The SMRR step 2 gives the true chemical formula C13H10N2O4, and indicates that this could be a polymorph mixture. The fact that the 19-1946 JCPDS-ICDD card gives a wrong formula (C13H10N2O) adds some pepper to the SMRR sample 3.
People working on organic and organometallic samples are quite frequently annoyed by the PDF incompleteness. They expect a lot from the addition of calculated powder patterns from the CSD.This was said to come for the end of 2002. We hope that this will be confirmed.