▎ 摘 要
Multi-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 center dot center dot center dot C distances of about 3.3 angstrom in them. As a result, the elongation of the C center dot center dot center dot 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 mte-nA and an open-shell singlet diradieal 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 dosed-shell molecules (e.g, linear, oligoacenes and graphene patches) 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 center dot center dot center dot Be distances are 2.67-2.84 angstrom, implying weak Be(s(2))center dot center dot center dot Be(s(2)) 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.