All substances around us consist of atoms. The types of atoms and their three-dimensional arrangement define the structure of materials, therefore the nature of materials. Since the properties and functions of materials relate directly to its structure, there exist extensive researches for various materials such as semiconductor, electronic, food, pharmaceutical, or life science related materials.
However, we can’t recognize the structure of materials at the atomic level because of the limited resolution mainly due to the wavelength, as long as we see objects with our eyes by using visible light. For example, we neither can distinguish a grain of table salt from that of sugar by their atomic level structures, nor can have a clear view of the turtle shell-shaped 6-membered rings (benzene rings) by just staring at the medicine for colds.
Recently, elucidation of molecular structures is becoming more common owing to the developments of various measurement techniques. Nuclear magnetic resonance (NMR), mass spectrometry (MS), and infrared spectroscopy (IR) are the typical examples. However, these spectroscopic techniques derive just a list of partial structures, and it is sometimes difficult to deduce the three-dimensional structure of a whole molecule. On the other hand, it is the molecular structure itself that is derived from the single crystal X-ray analysis (SCXRD). The single crystal analysis provides a unanimous conclusion that sometimes puts an end to arguments over molecular or crystal structures.
However, it is the fact that X-ray crystallography tends to be averted despite its efficiencies because it gives an impression to be difficult method requiring special knowledge. Through this series of articles, we would like to deliver an introductory course to the single crystal X-ray analysis to those who are not familiar with this technique. The course includes what X-ray crystallography is, what X-ray crystallography reveals, and how to solve the problems you will encounter in the future.