Crystallography is a catch-all term for a number of analytical techniques involving diffraction, an interference phenomenon. It essentially involves the scattering of light or particles by a material and using the pattern given out to determine structural details of the sample studied. Crystallography can include:
- Scattering of X-rays, neutrons or even electrons;
- Examination of materials with long range or short-range order;
- Study of powdered, thin film, single crystal or nanoparticle samples.
Chemical Crystallography typically covers the diffraction of X-rays (or neutrons) from powdered or single crystal materials that exhibit long range order with the intention of determining the three dimensional structure.
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Single Crystal X-ray Structure Determination
Light is a wave that has a phase and an intensity (or amplitude). When we record a diffraction pattern, we can typically measure the intensities, but the phase information is lost. Since the majority of the information is held in the phases, this is known as "The Phase Problem". A key part of determining a structure is solving this.
The final result gives a precise three dimensional model that not only depicts a small region of space (like a molecule), but how the crystal extends in all direction. It can therefore give information on long range interactions and correlations as well as bond distances, angles and other geometric parameters and even chirality. In this sense, structure determination from single crystal diffraction is a truly unique, and very powerful, analytical tool.
There are a couple of key challenges associated with the technique however:
- Unlike other analytical techniques, the whole diffraction pattern is needed (it is generally not possible to measure a small part and get a information on a small part of the material—it is all or nothing);
- The technique requires good quality, single crystals.
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Chemical Crystallography in Oxford
Chemical Crystallography in Oxford is carried out in the Small Research Facility in the basement of the Chemistry Research Laboratory. The facility comprises three single crystal X-ray diffraction instrument and one powder X-ray diffraction instrument as well as associated necessary equipment like microscopes and sample mounting equipment.
There are two primary routes for people wishing to have their structure determined:
- The Chemical Crystallography Analytical Service.
- Learn to do it yourself.
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