Rubidium fullerides

Fullerene, black and shiny like graphite, is the subject of active current research because of its interesting electronic properties. When allowed to react with rubidium metal, a superconducting material called rubidium fulleride, Rb3C6o, is formed. (We ll discuss superconductors in more detail in Section 21.6.) Carbon nanotubes are being studied for use as fibers in the structural composites used to make golf clubs, bicycle frames, boats, and airplanes. On a mass basis, nanotubes are up to ten times as strong as steel. 

In 1991, scientists at AT T Bell Laboratories discovered a new class of high-temperature superconductors based on fullerene, the allotrope of carbon that contains Cgo molecules (Sections 10.10 and 19.6). Called "buckyballs," after the architect R. Buckminster Fuller, these soccer ball-shaped Cgo molecules react with potassium to give K3C6o- This stable crystalline solid contains a face-centered cubic array of buckyballs, with K+ ions in the cavities between the Cgo molecules (Figure 21.16). At room temperature, K3Q,o is a metallic conductor, but it becomes a superconductor at 18 K. The rubidium fulleride, Rb C o, and a rubidium— thallium-Cfio compound of unknown stoichiometry have higher Tc values of 30 K and 45M8 K, respectively. 

Figure 10.15. A. NMR spectra of the rubidium fullerides K2RbC(sn (upper) and KRbCsC6o (lower), from Maniwa et al. (1993). B. Rb NMR spectra of the rubidium fulleride RbQo at various temperatures. Note the broad octahedral Rb resonance in the low-temperature phase progressively replaced by the narrower tetrahedral resonance above the phase transition temperature. From Tycko et al. (1993). Both diagrams used by permission of the copyright owners.

Electronic properties and sobd-state Rb and NMR studies of mesoporous tantalum oxide rubidium fulleride composites. 2005 17 1467-1478. 

Mesoporous tantalum oxide rubidium fulleride composites were synthesised by solution impregnation and characterised by Rb and C solid-state NMR and other methods. Rb solid-state NMR of the composite materials indicated the presence of two Rb environments associated with the walls or chaimels of the mesostructure as well as several resonances associated with various fulleride species. C solid-state NMR experiments showed the presence of multiple fulleride species as well as pure fullerene, depending on the level of reduction. ... 

---