Where possible, samples should be provided in a dry and loose form in a small vial. Drying crystals under vacuum should be avoided. If solvent loss or crystal decomposition appears to be a problem, the sample may be provided damp or in mother liquor.
Click here for information on crystal growth and sample preparation.
The sample submission and analysis procedure is as follows:
- Deposit your sample in the X-ray deposition box in 19 G 03, where there is also a microscope for you to evaluate the crystals. If you are sending the sample from an external location, obtain the mail address from your contact person in advance.
- The sample will be examined for suitablility under the microscope.
- If the sample is unsuitable, the possibilities for recrystallisation will be discussed.
- If the sample is satisfactory, it will be placed in the queue and assigned a sample number which will appear on all subsequent data, reports and communications.
- Fill out a Request Form (PDF, 183 KB) with the required information. External clients should use a different form. (PDF, 163 KB)
- The data collection will be commenced as soon as possible according to the number of preceding samples in the queue and the relative priority of the work. The duration of the data collection is usually 4-24 hours, depending on the crystal quality and the requirements of the experiment.
- The structure solution and refinement, generation of the report and tables, and the preparation of the diagram follows and usually requires 1-2 days, although complicated structures with large molecules or disorder can require considerably more time.
- The report, diagrams and any remaining crystals will be delivered to the client.
When filling out the Request Form, the following information is useful:
- Expected molecular formula. Where this has been deduced from elemental analysis, MS or NMR, these analyses should have been performed on the SAME sample from which the crystals have been prepared. Subsequent decomposition or contamination during recrystallisation can sometimes lead to unexpected results!
- Give the solvent used for crystallisation. This is important, as some crystals contain solvent molecules as part of the crystal lattice. Sometimes this solvent is so highly disordered that it is difficult to determine exactly what is present if information on the solvent used for crystallisation has not been provided.
- Sketch the expected structure or all alternatives if there is more than one possibility. If the structure is completely unknown, give as much information as possible, including the specifically known fragments and the reactants.
- State whether the compound is achiral, racemic or a pure enantiomer. For the latter, clearly indicate all known chiral centres and those which are still unknown.
- Give the desired atom numbering for the proposed structure, preferably according to the IUPAC nomenclature. It is very helpful to have this information before we start the analysis. Although we can renumber the molecules at any later date, this creates a considerable amount of additional work. It is not just a matter of editing the diagrams. All of the tables must also be regenerated, because the data deposited with the Cambridge Crystallographic Database must be consistent with the published work.