London Dispersion Enables the Shortest Intermolecular Hydrocarbon H•••H Contact

Neutron diffraction of tri(3,5-tert-butylphenyl)methane at 20 K reveals an intermolecular CH center dot center dot center dot HC distance of only 1.566(5) angstrom, which is the shortest reported to date. The compound crystallizes as a C3-symmetric dimer in an unusual head-to-head fashion. Quantum chemical computations of the solid state at the HSE-3c level of theory reproduce the structure and the close contact well (1.555 angstrom at 0 K) and emphasize the significance of packing effects; the gas-phase dimer structure at the same level shows a 1.634 angstrom C-H center dot center dot center dot H-C distance. Intermolecular London dispersion interactions between contacting tert-butyl substituents surrounding the central contact deliver the decisive energetic contributions to enable this remarkable bonding situation.