Phenalenyls (PLYs)
are important synthons in many functional and
electronic materials, which often display favorable molecule-to-molecule
overlap for electron or hole transport. They also serve as a prototype
for π-stacking pancake bonding based on two-electron multicenter
bonding (2e/mc). Unexpected near-doubling of the binding energy is
obtained for the positively charged PLY
2
+
dimer
with an effect similar to that seen for the positively charged olympicenyl
(OPY) radical dimer. This charge effect is reversed for the perfluorinated
(PF) dimers, and the negatively charged perfluorinated (PF) dimers
PF–PLY
2
–
and PF-OPY
2
–
become strongly bound. Long-range interactions
reflect these differences. Also surprising is that in this case the
pancake bonding corresponds to single-electron (1e/mc) or a three-electron
(3e/mc) multicenter bonding in contrast to the 2e/mc bonding that
occurs for the neutral radical dimers. The strong preference for a
large intermolecular overlap is maintained in these charged dimers.
Importantly, the preference for π-bonding in the charged dimers
compared to σ-bonding is strongly enhanced relative to the neutral
PLY dimers.
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