Early History of X-Ray Crystallography

The discovery of the optical microscope played an important role in the scientific revolution of the seventeenth century because it enabled one to directly view objects which were invisible to the naked eye. In 1667 Robert Hooke improved the microscope invented in the previous century in Holland and used it to examine the “microscopic” appearance of snowflakes and plants. Others were able to view for themselves the presence of very small objects and the structures of plants, hair, skin, bones etc. The development of X-ray crystallography at the beginning of the twentieth century by von Laue and the Braggs played an equally important role in the scientific revolution which has shaped our lives. The technique they discovered did not enable scientists to look at the molecular world by looking through a more powerful microscope, but it provided data which when processed enabled scientists to calculate the structures of molecules and appreciate their three-dimensional structures. It provided the zeitgeist of our time that the knowledge of the structure would lead to a more profound understanding of the function and properties of that class of molecule.

This chapter recounts the early history of the development of this important technique and describes how the early technical problems were overcome. It is a fascinating technique because unlike the optical microscope it required the development of a deeper understanding of the way in which the X-rays interact with the electron density in the planes of the crystal and the development of models in order to model this electron density satisfactorily. This chapter traces how these problems were overcome. In the early days, the structures of even simple organic molecules would take a PhD student several months or even years to solve the structure. In time and particularly since the 1950s, the development of more sophisticated equipment and the massive rise in computing power made it possible to solve the three-dimensional structure of an organic molecule within a few minutes with the latest detectors on a laboratory instrument. This successful trajectory has resulted in the ability to study ever more complex molecules and use smaller and smaller crystals. The structures of over a million organic and organometallic compounds are now archived in the most commonly used database, and this wealth of information creates a new set of problems for future generations of scientists.