1996 McCoy Award Recipient
Ben S. Freiser
Professor Chemistry

Having a Ball with Buckyball, Met-Cars, and FTMS

Ben S. Freiser was born in Pittsburgh, Pennsylvania. He obtained his B.S. in chemistry from the University of California in 1971 and his Ph.D. from the California Institute of Technology in 1977. While at Caltech, Freiser studied the photochemistry of ions in the gas phase, and in 1976 won the Herbert Newby McCoy Award for the "most outstanding student in chemistry." Freiser joined the Purdue chemistry department in 1976. He was head of the analytical division from 1984 to 1988. Freiser has won the Frank Martin Award for teaching excellence in chemistry and has been named one of the 10 most outstanding teachers in the School of Science six times. His research has earned him several prestigious awards, including the ACS Pure Chemistry Award, the Fresenius Award, the Akron ACS Section Award, the Baekeland Award, the Purdue Sigma Xi Award, and the Anachem Award.

Abstract of talk
The study of transition-metal containing ions in the gas phase offers the opportunity to probe the intrinsic chemical and physical properties of these species in the absence of complicating factors such as solvation and ion-pairing effects. The chemistry of these highly electronically and coordinatively unsaturated species is not only inherently interesting, but can provide important clues as to mechanisms occurring on surfaces and in condensed phases by yielding a better understanding of key steps and potential intermediates. Furthermore, obtaining quantitative data on metal ion-ligand bond energies and studying the periodic properties of metal ions as a function of their ground and electronic state structures are important in rendering the outcome of an organometallic reaction predictable.

Developments in Professor Freiser's group involving Fourier transform ion cyclotron resonance (FTICR) mass spectrometry have greatly enabled the study of gas-phase ion-molecule reactions in an unprecedented multistep fashion. These developments, together with the group's introduction of laser desorption for generating metal ions, have permitted a rapid advancement in the understanding of gas-phase transition metal ion chemistry. Recent highlights from this work will be discussed, including: (1) the chemistry and structure of metallo-carbohedrenes (met-cars); (2) metal-assisted derivatizations of Buckminsterfullerene; and (3) the photochemistry of metal-containing cations.

Research
A major breakthrough in Professor Freiser's research came in 1980 with the marriage of a laser ionization source to an ion cyclotron resonance (ICR) spectrometer to generate and study the gas-phase chemistry of simple metal ions. This has been and continues to be a major thrust of his work. With this technique, metal ions are generated directly by focusing a high-powered pulsed laser onto the pure metal. This method is so superior to those used previously that this finding has materially accelerated the study of metal ions in the gas phase. In fact, laser ionization is now commonly used by most workers in the field. Another milestone in Freiser's career was his initiation of studies of a wide variety of chemical systems with Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Freiser was in the forefront in recognizing and exploiting the potential of FTICR for fundamental chemical studies, and his group has published over 160 papers utilizing the instrument. During the past five years, Freiser's group has been active both in the development of new methodology for FTICR mass spectrometry and in the exploitation of laser desorption-FT1CR to open up exciting new areas in metal ion chemistry. A few of the many highlights are summarized here. Freiser's group has made outstanding contributions to the "Buckyball Story." In 1991 the group gained attention by generating and studying exohedral complexes of MC60+ (M = transition metal) and demonstrating unequivocally that these complexes exhibit different physical and chemical properties from the then-proposed endohedral C60 complexes reported by Smalley. This put to rest a five-year-old controversy over whether Smalley was really generating endohedral complexes in his supersonic source. This project now has evolved into a study of metal-assisted derivatization of fullerenes which has, thus far, been successful in uncovering several new com- pounds including a family of bis-Bucky complexes, M(C60)2+and C60(CH2)2,3 involving 4- and 5-membered ring structures on Buckyball (dubbed Buckybaskets). These studies also reveal fundamental structural and thermochemical properties of these new materials. The study of small metal clusters has, for some time, been the focus of intense investigation. One of the driving forces for these studies is their significance in understanding the nature of the reactive sites in heterogeneous catalysis. This connection is especially clear if one considers that, to a first approximation, the surface of a bulk structure is an assembly of clusters of various sizes and isomers. Freiser and his group recently have adapted a Smalley supersonic source to the FTICR (the second such system in the world) to study metal cluster ions, Mn + (n = 2-200). The first series of papers from Freiser's group report the most detailed product distribution and kinetic data yet obtained, yielding new structure-reactivity relationships. A new class of transition metal-carhon clusters named "metallo-carbohedrenes" or "met-cars" with the stoichiometry M8C12 has become the focus of intense investigation. The species, discovered by Castleman and coworkers, have been mainly observed as "supermagic" peaks in mass spectra obtained from supersonic metal cluster sources in which the He expansion gas is seeded with a hydrocarbon. Like the fullerenes, the metallo-carbohedrenes are of fundamental interest and also hold promise as important new materials. Investigations by Freiser's group have provided striking experimental evidence for corroborating the theoretically most stable structure of the met-cars. Lastly, Freiser's group pioneered the study of the photochemistry of metal-containing ions in the gas phase. In the past five years, Freiser has exploited the methodology developed in his laboratory to obtain critical metal-ligand bond energies. His group recently demonstrated the first examples of photoinduced ion-molecule reactions. This work not only yields absorption information in the near IR on ions at 10 '" M, but also yields fundamental mechanistic information on photocatalysis and analogous reactions in solution.