R James Cross
Member of Yale faculty since 1966
An important part of Physical Chemistry is the study of chemical systems under unusual conditions so that we may broaden our understanding of their behavior. In collaboration with Prof. Martin Saunders we have devised several ways of putting atoms and small molecules into fullerenes, where they remain trapped. These unusual compounds are stable, van der Waals molecules in that there is no chemical bond between the trapped atom and the carbon cage. Yet, they are very stable, since several C-C bonds must break to allow the atom to escape.
After heating fullerenes and cyanide in the presence of gas at 3000 atm and 650 C, up to 1% of the fullerene molecules contain the gas molecule. We can use this method to put He, Ne, Ar, Kr, Xe, CO, and N2 inside. The heavier species can be purified by HPLC, so we can measure spectral changes from the empty fullerenes. Using a beam of ions or fast atoms, we can shoot helium, neon, or nitrogen atoms through the fullerene wall, trapping them inside. We can also shoot tritium atoms into C60 by generating them at high energy in a nuclear reaction.
The NMR spectroscopy of 3He or H2 inside fullerenes is a useful diagnostic tool. The NMR line is intense and very narrow, and the position is very sensitive to the electronic structure of the fullerene, since the π-electrons partially shield the magnetic field. Adding electrons or groups to the fullerene causes large shifts in the resonance, and therefore 3He NMR can be used to study fullerene reactions.
We have collaborated with several groups that have used chemical reactions to open holes of various sizes in C60. We can then measure the rates and equilibrium constants for gases going in and out of the holes. We recently got both CH4 and NH3 inside.
B.S. Yale University, 1962
Ph.D. Harvard University, 1966
Postdoctoral Fellow, University of Florida
Alfred P. Sloan Fellowship, 1969
R. J. Cross & M. Saunders. Transmutation of Fullerenes. J. Am. Chem. Soc.2005, 127, 3044.
S. I. Iwamatsu, C. M. Stanisky, R. J. Cross, M. Saunders, N. Mizorogi, S. Nagase, & S. Murata. Carbon Monoxide Inside an Open Cage Fullerene. Angew. Chem. Int. Ed. Engl. 2006, 45, 5337-5340.
M. Frunzi, R. J. Cross, & M. Saunders. Effect of xenon on fullerene reactions. J. Am. Chem. Soc. 2007, 129, 13343.
R. J. Cross. Vibration-rotation spectroscopy of molecules trapped inside C60. J. Phys. Chem. A 2008, 112, 7152.
K. E. Whitener, M. Frunzi, S. Iwamatsu, S. Murata, R. J. Cross, & M. Saunders. Putting ammonia into a chemically opened fullerene. J. Am. Chem. Soc. 2008,130, 13996.