The investigation of the biphenylene (BP)‐tetracyanoethylene (TCNE) π‐molecular complex
is reported. The first study on this complex appeared in 1961 and was considered as
a charge transfer complex with a symmetric, co‐planar arrangement of the components.
Moreover, it was assumed that this arrangement is not only dictated by the formation
of a Mulliken‐type donor‐acceptor complex, but also by the electronic stabilization
of the “cyclobutadieneoid” central ring of biphenylene through complex formation.
Yet, crystal structure and associated computational analysis have not verified these
predictions so far. We found that factors other than charge‐transfer interactions
are most influential in the crystal formation. The low association constant in solution,
and the weak interaction between the components in the 1:1 crystal structure point
towards the low contribution of charge transfer interactions to their binding. Nevertheless,
the presence of these interaction is hinted by the color of its solution and verified
by theoretical calculations. Furthermore, Nucleus Independent Chemical Shift (NICS)
calculations were carried out to characterize potential changes in the (anti)aromatic
character of BP upon complex formation. The NICS(0) values of the rings of BP exhibit
tiny changes both in the BP‐TCNE dimer and in the crystal, which also suggests weak
electronic interactions between them.
