Atomic nitrogen encapsulated in fullerenes: Realization of a chemical Faraday cage

Fullerenes, C-60 and C-70, are ideal containers for atomic nitrogen. We wil l show by electron paramagnetic resonance (EPR) experiments that nitrogen i n C-60 keeps its atomic ground state configuration and resides in the cente r of the cage. This is the first time that atomic nitrogen is stabilized at ambient conditions. The inert shell of the fullerene protects the highly r eactive nitrogen from undergoing chemical reactions with the surroundings. The fullerene cage is the chemical analogue of the Faraday cage in case of electrical fields, i.e. it shields off the chemical reactivity. As for the free nitrogen atom, the spins of the three p-electrons of nitrogen in C-60 are parallel (S = 3/2) and the atom has spherical symmetry. Due to the cent er position of nitrogen in C-60, extremely sharp EPR lines are observed. Th is reflects the absence of a strong host-guest interaction and shows that t he individuality of nitrogen in the fullerenes is preserved. Further eviden ce for the almost interaction-free suspension of nitrogen in the fullerene cages is provided by g-factor measurements. These investigations show that magnetic shielding of the host molecules can account for the observed diffe rences between N@C-60 and N@C-70 The fullerene cage can be chemically modif ied without destroying the endohedral complex. The chemical modifications c hange the symmetry of the molecule which is observed through an additional fine structure in the EPR spectrum. Influences of the modifications on the stability of N@C-60 Will be discussed.