Structural and Spectroscopic Studies on Mesoporous Tantalum Oxide–Sodium Fulleride Composites with Conducting Fulleride Columns in the Pores

Abstract Mesoporous tantalum oxide–sodium fulleride composites were synthesized by solution impregnation and characterized by elemental analysis, X‐ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption–desorption, X‐ray electron photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID) magnetometry, variable‐temperature electron transport measurements, and solid‐state 13 C and 23 Na NMR spectroscopy. The room temperature conductivity pattern as a function of sodium reduction level displayed a minimum at n = 3.0 and a maximum at n = 4.5, where n is the formal charge on the fulleride. The variable‐temperature conductivity measurements demonstrated that the n = 0.5 and n = 4.5 materials were semiconductors. Solid‐state 23 Na NMR spectroscopy of the n = 0.5 composite exhibited three Na environments in the composites: two associated with the tantalum oxide walls and a third associated with the fulleride. The n = 3.0 and n = 4.5 materials showed a large build‐up of Na ions in the wall with no visible Na resonances associated with the fulleride, suggesting a structure in which the fulleride units exist as naked anions in one‐dimensional chains surrounded first by a layer of Na ions and then by a layer of mesoporous tantalum oxide. Solid‐state 13 C NMR experiments showed more than one fulleride species in both the n = 0.5 and the n = 4.5 composites, as well as pure C 60 in the n = 0.5 material, but almost exclusively C 60 3– in the n = 3.0 material. The retention of carbon throughout reduction suggests that polymerization may have occurred, however this could not be verified by 13 C NMR spectroscopy, because the region where sp 3 fullerene resonances normally appear was obscured by solvent peaks.