A Piggyback Ride for Transition Metals: Encapsulation of Exohedral Metallofullerenes in Carbon Nanotubes

Abstract

We have developed a method that enables the efficient insertion of transition-metal atoms and their small clusters into carbon nanotubes. As a model system, Os complexes attached to the exterior of fullerene C60 (exohedral metallofullerenes) were shown to be dragged into the nanotube spontaneously and irreversibly due to strong van der Waals interactions, specific to fullerenes and carbon nanotubes. The size of the metal-containing groups attached to C60 was shown to be critical for successful insertion, as functional groups too bulky to enter the nanotube were stripped off the fullerene during the encapsulation process. Once inside the nanotube, Os atoms catalyse polymerisation and decomposition of fullerene cages, which is related to a much higher catalytic activity of metal atoms situated on the surface of the fullerene cage, as compared to metal atoms in endohedral fullerenes, such as M@C82. Thus, exohedral metallofullerenes show promise for applications in catalysis in carbon “nano” test tubes.

Fullerene-driven encapsulation of a luminescent Eu(iii) complex in carbon nanotubes

“…Similar phenomena were previously reported for fullerene metal 55 complexes which are too large to fit within SWCNTs. [40] Nevertheless, several 1·[EuL 4 ] were found in wider than average 4 ] assemblies were observed along the same tube, it was evidenced that the orientation of the single assembly was coherent with that of the others, proving the efficient role of the C 60 as directing agent in the encapsulation procedure. Moreover, a certain degree of 15 regularity in the spacing between the units could be observed, indicating isolation of the luminophores within the structure by C 60 cages of neighbouring molecules thus preserving their luminescent properties by preventing parasite inter-chromophoric quenching phenomena.…”

“…More interestingly, 1·[EuL 4 ]@SWCNTs exhibited distinct organization. Indeed, several fullerene cages were observed within the internal cavity of SWCNTs characterized by an 40 internal diameter equal or higher than 2.7 nm (Fig. 3), which corresponds to the minimum diameter required for containing 1·[EuL 4 ] (Fig.…”

“…C 60 and C 70. In fact, the common nature of the two materials, together with the perfect geometrical match of 35 the shape of a fullerene and the inner nanotube surface of singlewalled CNTs (SWCNTs), results in a spontaneous encapsulation. [8] The use of CNTs as templating nano-containers has recently started to draw attention as a possible strategy for the synthesis of 40 novel highly organized photonic materials. It is well established that the emission properties of a chromophore, in terms of color and intensity, are extremely sensitive to the environment.…”

“…Hence, with the aim to 35 improve both the filling load and the luminescence of the resulting hybrid material, we decided to exploit the unique CNT-C 60 interaction to vehiculate LnCs inside CNTs. Inspired by the "nano-carriers" approach as developed by Khlobystov et al [29] who demonstrated the effectiveness of using fullerenes as 40 vehicles for inserting transition metal complexes inside SWCNTs, we also decided to use C 60 to facilitate and direct the entrance of the LnC within the carbonaceous cavity. To pursue our goal, we selected the bright tetrakis(2-naphtoyltrifluoro-acetonato) Eu(III) complex ([EuL 4 ]·NEt 4 ) [18a,30] 45 as a guest molecule.…”

“…Similar phenomena were previously reported for fullerene metal 55 complexes which are too large to fit within SWCNTs. [40] Nevertheless, several 1·[EuL 4 ] were found in wider than average -moieties. …”