Professor Ichikawa and myself share an interest in two areas of research. Our major common interest focuses on experimental and theoretical studies of the structures and properties of polybismuth ions. The other area of shared interest relates to supramolecular chemistry and specifically to research on encapsulated macroammonium chloride complexes. This report will be limited to a description of our collaborative research on homopolyatomic ions.
Bismuth possesses a number of unusually low oxidation states below the familiar Bi(III) and, in fact, bismuth has become the classical example of an element forming a series of homopolyatomic ions. The lower oxidation states of bismuth are represented by the entities Bi53+, Bi82+ and Bi95+ and these are the subject of our collaborative studies. Our initial interest was concerned with the tripositive Bi53+ ion and we completed a paper entitled "Neutron Diffraction of Homopolyatomic Bismuth Ions in Liquid Bi5(AlCl4)3 and ab Initio Study of the Structure and Bonding of the Isolated Bi53+ Ion" which was authored by Professor K. Ichikawa and his students T. Yamanaka and A. Takamuku (experimental aspects) and by myself (quantum chemistry). The paper has been submitted for publication in the American Chemical Society journal Inorganic Chemistry and received favorable reviews. This research is being continued with two specific goals and these concern studies of regiopreferences in heteropolyatomic systems and studies of the electronic spectra of the cluster ions.
To date, our theoretical studies of Bi53+ have focused on the bipyramidal structure. We will now extend these studies to also include the rectangular pyramidal structure. Modern methods of topological electron density analysis will be used to delineate the factors that are responsible for the energetic preference of the bipyramidal structure. A better understanding of these factors will have important practical consequences and will lead to experimentally testable predictions. The theoretically determined charge differences on non-equivalent cluster positions suggests, for example, preferences for the regioisomers of mixed clusters that incorporate an isoelectronic non-Bi atom at a cluster site. These insights will be used in attempts at the realization of novel materials by design.
Our studies of the Bi53+ ions have shown that the electronic spectra cannot be predicted based on the molecular orbitals of the ground state. The original assignments of the electronic spectra based on empirical MO theory are therefore without merit. For these highly charged systems, the Koopman theorem does not hold and the computation of electronic spectra becomes more involved. We will characterize the excited states of Bi53+, Bi82+ and Bi95+ using modern theoretical methods for the computation of excited states. With these higher level quantum-mechanical methods, we will be able to assign the UV/Vis absorptions which have been measured by Mr. Shimomura in Professor Ichikawa's laboratory. Such knowledge will be highly pertinent to the advancement of the understanding of the electronic structure of electron-poor clusters in general.
The JSPS fellow prepared four lectures for delivery on five occasions during his fellowship term in Japan.
(a) A lecture on the topic "DNA Chemistry related to Environmental Chemistry." was delivered on Tuesday, July 8, 10:30-12:00, at the Graduate School for Environmental Earth Studies, University of Hokkaido.
(b) A lecture on the topic "The Cation-Dinitrogen Interaction. From Dative Bonding Theory to Problems in Chemical Toxicology." was delivered on Friday, July 11, 13:30-15:00, in the Department of Biochemical Engineering and Science (Host: Professor Hiroshi Kashiwagi), Department of Biochemical Engineering and Science Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Kwazu 680-4, Iizuka 820. This lecture also was presented on Friday, July 18, 10:30-12:00, at the Institute for Molecular Science (Host: Professor Suehiro Iwata), Myodaiji, Okazaki 444.
(c) A lecture on the topic "Highly Dipole Aligned Organic Molecular Crystalline Materials for Nonlinear Optics" was delivered on Wednesday, July 23, 10:30-12:00, in the Graduate School for Environmental Earth Studies, University of Hokkaido. This event was co-sponsored by the Japan Chemical Society.
(d) A lecture on the topic "Topological Electron Density Analysis of Electron-Poor Bismuth Clusters" was delivered on Thursday, July 24, 13:30-15:00, to the Faculty of Science (Host Prof. Noro) of the University of Hokkaido.
This was my first trip to Japan and it is difficult to write about my thoughts and impressions since I returned only such a short time ago. I continue to reflect on my trip and I am only just beginning to start several email contacts. Thus, I will limit myself to relatively tangential facts.
First of all, I would like to express my gratitude to my host, Professor Ichikawa, for inviting me and for organizing such a wonderful schedule for me. From the very first day, when my host picked me up at Chitose airport, Professor Ichikawa took care of all aspects of my well-being in a most considerate fashion. I have enjoyed the many professional engagements we have had and I have cherished Professor Ichikawa's mentorship and his friendship.
My stay at the University of Hokkaido, Sapporo, in the group of Professor Ichikawa, my visits to the Department of Biochemical Engineering and Science of the Kyushu Institute of Technology, to the Institute for Molecular Science in Okazaki, to the Department of Chemistry of Rikkyo University, and my attendance of the 8th International Conference on Bioinorganic Chemistry in Yokohama have allowed me to experience many facets of Japanese Science. One of the impressions I got early on and that was more and more substantiated during the period of my stay concerns the high degree of interdisciplinary orientation which has already been realized in the chemical research in Japan. At the University of Hokkaido, I was in a department of Environmental Earth Science which strives to use a broad arsenal of scientific disciplines to contribute to the higher goal of understanding the complex interrelationships in the environment. At KyuTech, I learned about an extraordinary model for the integration of education in computer science and in science. At the Institute for Molecular Science, I saw how a multidisciplinary approach is used to learn fundamentals about structure and bonding and how one can go about transferring this knowledge to applied molecular science and the fabrication of new materials. The overwhelming majority of the contributions to the "Bioinorganic Chemistry" conference, of course, also represented the fruits of interdisciplinary research and the very strong Japanese presence, both from academia and from industry, demonstrated a very strong commitment to inter- and multidisciplinary approaches.
The frontiers of science are, of course, not only shifting into the areas between the classical disciplines but the conduct of frontier science in the late twentieth century also is changing in that research has become a truly international affair. As a German living in the United States, I am very aware of the traditionally close ties between North America and Europe as well as within Europe and at all levels of education. Japanese professors, of course, always have been experienced and passionate travelers and there also have always been a good number of Japanese post-docs seeking international refinement. On my trip to Japan, I have now had the opportunity to see that many efforts are being undertaken to foster such international ties even earlier and with the goal of creating a broader base. Many of the graduate students read and spoke fluent English and they showed interest in spending a year abroad. I met many international students who came to Japan on government fellowships to pursue graduate degrees in Japan.
It was truly a very great honor for me to be selected as the recipient of a fellowship by the Japan Society for the Promotion of Science. It is only for this generous fellowship that I could afford to travel to Japan and to visit so many places of scientific excellence and to speak with so many talented and enthusiastic colleagues and students. I am looking forward to cultivating and strengthening these contacts in the years to come. I hope to do so be returning the hospitality I have so greatly enjoyed to visitors from Japan to MU and I also very much would like to return to Japan for many more visits in future. It is already absolutely clear that I very much want to return to Japan with my family although I am not sure how I will be able to accomplish this goal.
My time in Japan was exhilarating; every day brought new experiences and life was full of adventures and excitement. Since I returned, I have spent a considerable amount of time internalizing the broad spectrum of new experiences. To keep track of events, I have put together an online chronology of my trip in electronic form on the world wide web at URL http://www.missouri.edu/~chemrg/vitpub/Japan_1997.html. The site has been under permanent construction ever since I came back form Japan. While I first build this site merely for me to keep track of events, I think the site has already taken up other functions as well. My Japanese friends dial in with their browsers and we all stay in more frequent and closer contact than we might otherwise have. Better even, I have directed several of my American and German friends to this site so that they can get an idea of what the trip was like and, perhaps, stimulate their interest in visiting Japan by themselves.