Department of Chemistry - University of Zurich


What can a crystal structure analysis do for you?

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Why do an X-ray crystal structure determination?

An X-ray crystal structure determination is almost the ultimate analysis. No other analytical technique currently available can deliver such complete and unambiguous information about the nature of the substance being investigated. The X-ray diffraction experiment provides a 3-dimensional map of electron density and therefore a complete 3-dimensional "picture" of the substance in question.

With the modern instrumentation now available, the diffraction experiment and initial solution of the structure can often be completed within just a few hours. Therefore, a crystal structure analysis has become the analytical method of choice when suitable crystals are available, because the speed of the analysis is approaching a similar timescale to that of other analytical methods (including interpretation of the spectra), and it provides unsurpassably detailed and unequivocal structural information.

An X-ray crystal structure determination is often used merely to confirm that the product of a chemical reaction or an isolated natural product is indeed the expected or predicted compound. In reality, the structure determination provides a wealth of information about the compound being investigated, much of which is often under-utilised.

Provided good quality crystals are available and there is no complex disorder present, the following information can be obtained from an analysis:

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Disadvantages of the technique

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When should you consider employing an X-ray structure analysis?

Ideally, it would seem desirable to conduct an X-ray crystal structure determination for every substance that is synthesised or isolated, as this would quickly reveal the precise nature of the product and probably save hours of time evaluating and interpreting other spectra. This is particularly important if an unexpected and exciting new product has resulted, because the interpretation of other spectra may be very complicated and bothersome if the reaction has taken an unexpected and unknown course.

As the modern instrumentation has enabled the diffraction experiment to be completed within just a few hours, the above ideal can now be achieved quite readily. The biggest remaining hindrance to the application of this ideal is probably the effort required to grow single crystals of adequate quality within a reasonable timeframe.

While an X-ray structural analyses can usually be used to determine the molecular composition and connectivity of a compound without any prior knowledge, it is certainly useful to know, before commencing the analysis, what the compound is expected or likely to be. You should also try to ensure that you are not submitting an unexpected or unwanted product, simple side-product or unreacted reactant. In this way, you will save unnecessary analyses, as well as your own time and embarrassment. Therefore, whenever possible, at least preliminary MS, IR and NMR spectra should be recorded and evaluated before the crystals are submitted for an X-ray structure determination, so that the unnecessary determination of trivial or uninteresting structures can be avoided. However, if the spectra reveal that you have a product of interest, even if its structure cannot be deduced easily, you should not hesitate to request an X-ray crystal structure determination.

In the majority of cases, it is recommended that an X-ray crystal structure determination be carried out whenever one or more of the following situations arise:

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last update: Friday, 09-Dec-2016 13:25:37 CET
Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland