Synthesis and 83 Kr NMR spectroscopy of Kr@C 60 .

Synthesis of Kr@C 60 is achieved by quantitative high-pressure encapsulation of the noble gas into an open-fullerene, and subsequent cage closure. Krypton is the largest noble gas entrapped in C 60 using 'molecular surgery' and Kr@C 60 is prepared with >99.4% incorporation of the endohedral atom, in ca. 4% yield from C 60 . Encapsulation in C 60 causes a shift of the 83 Kr resonance by -39.5 ppm with respect to free 83 Kr in solution. The 83 Kr spin-lattice relaxation time T 1 is approximately 36 times longer for Kr encapsulated in C 60 than for free Kr in solution. This is the first characterisation of a stable Kr compound by 83 Kr NMR.