Fullertubes: Cylindrical Carbon with Half-Fullerene End-Caps and Tubular Graphene Belts, Their Chemical Enrichment, Crystallography of Pristine C₉₀-<i>D</i>_<i>5h</i>(1) and C₁₀₀-<i>D</i>_<i>5d</i>(1) Fullertubes, and Isolation of C₁₀₈, C₁₂₀, C₁₃₂, and C₁₅₆ Cages of Unknown Structures

Abstract

We report a chemical separation method to isolate <i>fullertubes</i>: a new and soluble allotrope of carbon whose structure merges nanotube, graphene, and fullerene subunits. Fullertubes possess single-walled carbon nanotube belts resembling a rolled graphene midsection, but with half-fullerene end-caps. Unlike nanotubes, fullertubes are reproducible in structure, possess a defined molecular weight, and are soluble in pristine form. The high reactivity of amines with spheroidal fullerene cages enables their removal and allows a facile isolation of C₉₆-<i>D</i>_<i>3d</i>(3), C₉₀-<i>D</i>_<i>5h</i>(1), and C₁₀₀-<i>D</i>_<i>5d</i>(1) fullertubes. A nonchromatographic step (Stage 1) uses a selective reaction of carbon cages with aminopropanol to permit a highly enriched sample of fullertubes. Spheroidal fullerenes are reacted and removed by attaching water-soluble groups onto their cage surfaces. With this enriched (100-1000 times) fullertube mixture, Stage 2 becomes a simple HPLC collection with a single column. This two-stage separation approach permits fullertubes in scalable quantities. Characterization of purified C₁₀₀-<i>D</i>_<i>5d</i>(1) fullertubes is done with samples isolated in <i>pristine</i> and <i>unfunctionalized</i> form. Surprisingly, C₆₀ and C₁₀₀-<i>D</i>_<i>5d</i>(1) are both <i>purplish</i> in solution. For X-ray crystallographic analysis, we used decapyrrylcorannulene (DPC). Isomerically purified C₉₀ and C₁₀₀ fullertubes were mixed with DPC to obtain black cocrystals of 2DPC{C₉₀-<i>D</i>_<i>5h</i>(1)}·4(toluene) and 2DPC{C₁₀₀-<i>D</i>_<i>5d</i>(1)}·4(toluene), respectively. A serendipitous outcome of this chemical separation approach is the enrichment and purification of several <i>unreported</i> larger carbon species, e.g., C₁₂₀, C₁₃₂, and C₁₅₆. Isolation of these higher cage species represents a significant advance in the unknown <i>experimental</i> arena of C₁₀₀-C₂₀₀ structures. Our findings represent seminal <i>experimental</i> evidence for the existence of <i>two</i> mathematically predicted families of fullertubes: one family with an axial <i>hexagon</i> with the other series based on an axial <i>pentagon</i> ring. Fullertubes have been predicted theoretically, and herein is their experimental evidence, isolation, and initial characterization.