Atomic nitrogen encapsulated in fullerenes: Effects of cage variations

The synthesis and EPR spectroscopic investigations of a family of six endoh edral fullerenes, namely, N@C-60 (1), N@C-61(COOC2H5)(2) (2), N@C-66(COOC2H 5)(12) (3), N@C-66(COOC2D5)(12) (4), N@C-61(COOC2D5)(2) (5), and N@C-70 (6) , containing atomic nitrogen in the S-4(3/2) ground state is described. The parent systems N@C-60 (1) and N@C-70 (6) were synthesized by nitrogen ion implantation. The syntheses of the C-2 upsilon-symmetric monoadducts 2 and 5 and the Ti, symmetric hexaadducts 3 and 4 exhibiting well-defined cage di stortions were accomplished via cyclopropanation with the corresponding mal onates, With respect to these additions the reactivity of 1 is indistinguis hable from that of empty C-60 The quartet electronic spin of the encapsulat ed N-atoms is a very sensitive probe for cage modifications. In the monoadd ucts 2 and 5 a permanent zero field splitting (ZFS) tensor with rigidly ali gned axes was revealed reflecting the intrinsic droplet like cage distortio n. In contrast, no fine structure due to intrinsic distortions was monitore d in the ESR spectra of the highly symmetric hexaadducts 3 and 4. In these cases only matrix-induced distortions of the cage lead to ZFS interactions. In solution fluctuations of the ZFS tensor are the major source of spin re laxation. The root-mean-square value of this collision-induced fluctuating ZFS interaction as estimated from relaxation data fur N@C-60 (1) and the he xaadduct 3 is in the range of the ZFS interaction measured for the monoaddu ct 2.