C36, a hexavalent building block for fullerene compounds and solids

Structures and energies are calculated at the DFTB level for C36-based fullerenes, hydrides, oligomers and solids. The two fullerenes with minimal pentagon adjacencies are isoenergetic. The isomer implicated in recent experiments has C6v broken symmetry, a small HOMO–LUMO gap and can gain or lose up to six electrons. C36 forms stronger inter-cage bonds than larger fullerenes. A favoured σ-bonding pattern rationalises a dimer with ten times the stabilisation of (C60)2, a linear polymer, a ‘superbenzene’ oligomer, a ‘supergraphite’ layer and a hexagonal close-packed solid with a monomer stabilisation of 522 kJ mol−1 and a d-spacing (6.82 Å) compatible with the experiments.