Prof Alexandra M Z Slawin
Our primary interest is in the determination of 3 D structures of molecules using single crystal X-ray crystallography
Single crystal X-ray diffraction is the structural chemist's most important tool for obtaining accurate and precise information on the structure of a material.
For many years this technique has been regarded as a routine method of structure solution. There is continuing growth in demand for high-quality structural work. The practicalities of the technique have developed quickly over the past 10 years.
Charge Coupled Device [CCD] detectors have increased the speed of data collection and the ability to deal with more difficult samples. Typically, 10 years ago a medium sized problem might have taken 3-4 days collection time whereas now with a standard CCD-based system and a sealed tube generator this data collection can be accomplished within hours. This is not meant to understate the difficulties of the technique. Collecting a data set is now ‘easy’ but converting that data set into an answer and refining it can prove very time consuming.
Typically over 1000 data are collected per year in St Andrews. In a high throughput lab dealing with a wide range of samples, including large organic problems, small organic chiral systems, organometallic and zeolitic type samples, there is a clear need for both Mo and Cu radiation.
We have installed two MM-007 high-brilliance generators; a molybdenum system which is equipped with VariMax™optics and two detectors, an AFC8/Saturn 70 on one port and our three year old AFC7/Mercury on the other port. The other generator, a Cu MM-007, is equipped with an AFC10/Saturn 92 (Figure 2).
We also have a bench top SCXMini which uses a sealed tube generator and CCD detector and is optimised for rapid highly automated use.
A fifth CCD system is completely robotically controlled. Samples are munted on loops and put into a sample carousel. The de user provides basic information on the sample and the system then automatically centers the crystal and collects the data before emailing the user with information on the outcome. This system is capable of continuous 24 hour a day use under completely automatic operation.
All five systems have X-streamTM
low temperature accessories and helium-purged optics.
The systems collect and reduce the data in the lab but are networked to allow rapid transfer of reduced data as well as the use of offline integration facilities. We use CrystalClear™ as the main indexing/integration software. The ability to make use of d*TREK® and TwinSolve is especially helpful.