Design and Analysis of a Molecular Tool for Carbon Transfer in Mechanosynthesis

Mechanosynthesis of a target class of graphene-, nanotube-, and diamond-like structures will require molecular tools capable of transferring carbon moieties to structures that have binding energies in the range of 1.105 to 1.181 aJ per atom (159 to 170 kcal mol⁻¹). Desirable properties for tools include exoergic transfer of moieties to these structures; good geometrical exposure of moieties; and structural, electronic, and positional stability. We introduce a novel carbon-transfer tool design (named by us "DC10c"), the first predicted to exhibit these properties in combination. The DC10c tool is a stiff hydrocarbon structure that binds carbon dimers through strained -bonds. On dimer removal, diradical generation at the dimer-binding sites is avoided by means of -delocalization across the binding face of the empty form, creating a strained aromatic ring. Transfer of carbon dimers to each of the structures in the target class is exoergic by a mean energy >0.261 aJ per dimer (>38 kcal mol⁻¹); this is compatible with transfer-failure rates of ∼10⁻²⁴ per operation at 300 K. We present a B3LYP/6-31G(d,p) study of the geometry and energetics of DC10c, together with discussion of its anticipated reliability in mechanosynthetic applications.