om7b00082_si_001.pdf (3.21 MB)
Remarkable Magnetic Coupling Interactions in Multi-Beryllium-Expanded Small Graphene-like Molecules with Well-Defined Polyradical Characters
journal contribution
posted on 2017-04-03, 14:19 authored by Meiyu Song, Xinyu Song, Yuxiang BuMulti-beryllium-expanded
small graphene-like molecules including oligoacenes (mBe-nA) and graphene patches (mBe-GP)
are computationally designed through introducing two or three Be atoms
into the specific benzenoid rings of the graphene-like molecules,
leading to replacement of some C–C bonds by the C–Be–C
linkages with elongated C···C distances of about 3.3
Å in them. As a result, the elongation of the C···C
bonds and insertion of more Be atoms make the two radical moieties
in each molecule relatively separated and their interaction relatively
weak. Both density functional theory and CASSCF calculations indicate
that all these multi-Be-expanded graphene-like molecules exhibit well-defined
polyradical characters: an open-shell singlet diradical for all mBe-nA and an open-shell singlet diradical
or quintet tetraradical for mBe-GP depending on the
Be-insertion patterns of the patches. The main findings in this work
are that (i) a switching from the parent graphene-like closed-shell
molecules (e.g., linear oligoacenes and graphene patches) to the open-shell
singlet (diradical) or quintet (tetraradical) ground states can be
realized by introducing Be as linkers into the graphene-like molecules;
(ii) more importantly, the spin-coupling interactions of such mBe-nA and mBe-GP are
remarkably large; and (iii) in these Be-modified molecules the Be–C
bonds exhibit considerable covalent character and the Be···Be
distances are 2.67–2.84 Å, implying weak Be(s2)···Be(s2) metallophilic interaction. This
work would open a new perspective for the rational design of perfect
and stable singlet diradicals or polyradicals with large spin-coupling
constants on the basis of small closed-shell graphene-like molecules
by multimetal incorporation and also encourage experimentalists to
pursue and realize these interesting structures with enhanced magnetic
properties in the future.