Search

SINCE the discovery of fullerenes1, efforts have been made to trap metal atoms inside fullerene cages2, and both endohedral3,4 and exohedral5,6 metallofullerenes have been synthesized. There is, however, a third possibility: a 'networked' metallofullerene, where the metal atom is incorporated into the carbon cage. Here we report the results of experiments to study the structure and reactivity of gas-phase fullerenes doped with niobium (NbCn+ with n = 28–50). These experiments, which use injected-ion drift-tube tech-niques, indicate that for fullerenes containing an even number of carbon atoms the metal is endohedral, but for fullerenes with an odd number of carbon atoms, the niobium metal is bound as a part of the carbon cage. Thus, networked metallofullerenes appear to be a stable class of metallofullerene. We suggest that such metallo-fullerenes can form if the metal atom retains sufficient electron density to form several strong covalent metal–carbon bonds.

METALLOFULLERENES1,2consist of metal atoms trapped inside closed fullerene cages. Virtually nothing is known about the mechanism of metallofullerene synthesis, although the possibility of a condensed-phase mechanism has been suggested in recent studies3,4. Here we show that laser vaporization of a La2O3/graphite rod produces a number of LaC60+ isomers, including the endohedral metallofullerene and a variety of different isomers in which lanthanum seems to be bound to polycyclic polyyne rings. When heated, nearly all of the different ring isomers convert spontaneously into metallofullerenes, trapping the metal atom inside the fullerene cage with remarkably high efficiency (>98%). We suggest that in the first step of this annealing process the lanthanum atom acts as a nucleation centre and the carbon rings arrange themselves around the lanthanum atom before converting into a fullerene cage.

The size and shape of amyloid-β protein assemblies have been studied using electrospray-ionization ion-mobility mass spectrometry, and the protein tetramers and dodecamers have been identified as an important oligomerization state in the development of neurodegenerative disease.