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 C–H···H–C distance of only 1.566(5) Å, 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 Å at 0 K) and
emphasize the significance of packing effects; the gas-phase dimer
structure at the same level shows a 1.634 Å C–H···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.