Methyl groups bound
to electronegative atoms, such as N or O, are
recognized to participate in tetrel bonding as Lewis acids. On the
other hand, the capability of methyl groups bound to electropositive
atoms, such as B or Al, to act as Lewis bases has been recently reported.
Herein, we analyze the combination of these two behaviors to establish
attractive methyl···methyl interactions. We have explored
the Cambridge Structural Database to find experimental examples of
these dimethyl-bound systems, finding a significant degree of directionality
in the relative disposition of the two methyl groups. Moreover, we
have carried out a comprehensive computational analysis at the DFT
level of the dimethyl interactions, including the natural bond orbital,
energy decomposition analysis, and topological analysis of the electron
density (QTAIM and NCI). The dimethyl interaction is characterized
as weak yet attractive and based on electrostatics, with a non-negligible
contribution from orbital charge transfer and polarization.