Experimental Evidence for the Missing and Theoretically Predicted [5,5] C150-D5h Fullertube and Isolation of a Second C150 Isomer

Novel allotropes of elemental carbon (e.g., fullerenes, carbon nanotubes, and graphene) are exciting. In 2019, nanotubular fullerenes (fullertubes) were experimentally discovered as a family of segmental, tubular molecules. We report the longest fullertube isolated to date, from 130 atoms in 2023 to now 150 carbon atoms. We have purified two structural isomers of C150. The late-eluting C150 species (Isomer II) represents the largest soluble fullertube/fullerene pristine molecule successfully isolated. From a total pool of 335,568 isolated-pentagon rule (IPR) candidate structures, surprisingly only three fullertube possibilities emerge. Isomeric purification of C150 was achieved via chemical selectivity (Stage 1) and HPLC (Stage 2). Isolated C150 fullertubes were characterized via mass spectrometry, XPS, Raman, and anisotropic polarizabilities and compared with DFT computations. Consistent with an established paradigm in the literature for fullertube structural assignments, we correlated chromatographic data (ln capacity factor, k′) in a plot of experimental HPLC data versus DFT-calculated anisotropic polarizabilities. Results indicate Isomer I is indistinguishable between [9,0] C150-D3h or [9,0] C150-D3. However, for Isomer II, multiple measures of experimental evidence (combined with DFT calculations) both support the decades-missing [5,5] C150-D5h fullertube structure long predicted by the literature. Plainly stated, the D5h assignment of a C150 fullertube structure is a strong prediction pending direct imaging confirmation with atomic resolution TEM.