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Crystal Structure and Molecular Motion in Solids

Aims to clarify the relation between crystal structure and molecular motions in solids

You may imagine that the molecules are static in solids. In fact, however, the molecules and ions show miscellaneous motions in solids, and these motions can determine the physical properties of materials. From this point of view, we are studying the relationship between the crystal structure and molecular motions in solids. X-ray diffraction method is applied to examine the crystal structure. In medical science, X-ray is used to examine inside of human bodies, such as Rontgen film, but in chemistry, structure and arrangement of molecules can be visualized by use of it. For example, the molecular structure of tetrachloro-m-xylene (TCMX) is shown in Figure 1.


Figure 1

The crystal structure determined by X-ray method is illustrated in Figure 2. In this figure, the colors are depicted such that the number of electrons is greater, the color becomes redder. In the center of figure, we can see the benzene ring as smaller hexagon, surrounded by 6 substituents as larger hexagon. We can also see that no difference is noticed among the substituents, that is, chlorine atoms and methyl groups cannot be distinguished.


Figure 2

This may come from the orientational disorder of TCMX molecules in the crystal, or, the molecules undergo very rapid motion about their (pseudo)6-fold axis. To elucidate which is better explanation, we used nuclear magnetic resonance technique, and the rapid molecular motion is observed. As described here, our studies aims to clarify the relation between solid state structure and molecular motion, hopefully leading the discovery of new functional materials.

Messages to high school students

the reason why I choose chemistry course
In my days in high school, I prefer studying physics not chemistry; mainly because the exercise in physics could be solved logically, but those in chemistry required a lot of things to memorize. Unfortunately, I could not pass the entrance examination in physics; I should choose chemistry as my course. After graduating from high school, I had occasionally read "Origin of Life", and I interested so much in biology; I was a bad student at that time. HOWEVER, the first lecture in chemistry at University, I became to LOVE chemistry. That lecture was presented in quite clear manner and was easy to understand. The professor gave straightforward route to realize the intrinsic matters which is not offered the reasons in high school textbooks but required to remember. He also indicated that chemistry is quite interesting, and students are required to think deeper; but it made me so exciting. Accordingly, I decided to enter his laboratory to accomplish my graduation research, and to learn various things about scientific thinking from him. There also were many senior students full of motivation in the laboratory. I absorbed a lot of things from them, and really enjoyed learning for 6 years. To my surprise, I become teacher now in university. As I could meet the professor I can respect, I wish everyone has such chance. And I will try to do my best, so that someone can think me as a good teacher.

after entering university
At first, please never forget that the study continues after entering the university; to enter the university should not be the goal. The duty of the student is "study". University students may think the days in university are dull, but it is "NO": you should not spend time to do nothing. I want you to think about and make an effort to realize your future. Furthermore, I require you to be interested in various things. You can study not only chemistry but also other fields of science. At the same time, you may read several newspapers every day to know social movements, read a lot of books, join a club...: there are so many issues you can do. You should not narrow your possibility by shrinking your interest in immediately useful matters only. It is the special privilege of the youth that have time to work on various things. I hope you to do your best.

studies in university
When you become 4th grade student, you should decide a theme of a graduation research. A problem at this point is that the research is most advanced all over the world, that is, no one knows the results. Reversely, you have to gain the knowledge between the high school level and the level of the world top in only 3 years. It's impossible to teach you all matters necessary in the lectures. Therefore, you should advance your knowledge by yourself. Please remember that you cannot use the excuse: "I have not learned it yet in lectures". Primarily, human being is full of curiosity. You can remember the pleasure when you could figure out something that couldn't formerly. I wish you can enjoy the fun of the learning at university.

Hiroshi OHKI
Hiroshi OHKI Chemistry