With the same Clar formulas, do the two-dimensional sandwich nanostructures X-Cr-X (X = C4H, NC3 and BC3) behave similarly?

The "perturbation" effects (i.e. hyperconjugation, electronegativity, and conjugation) on the structural, electronic, and magnetic properties of three kinds of two-dimensional (2D) X-Cr-X (X = C4H, NC3 and BC3 monolayers) sandwich nanostructures were systematically investigated by means of spin-polarized density functional theory (DFT) computations. Although all these 2D sandwich systems energetically prefer the same structural pattern and are featured with the same Clar formulas, their electronic and magnetic properties are significantly influenced by the "perturbations". Especially, a very strong π conjugation through the vacant p orbital of the B atom in BC3 leads to its sandwich structure with antiferromagnetic and conducting characters, which are in stark contrast to the non-magnetic and semiconducting characters of C4H-Cr-C4H and NC3-Cr-NC3. These findings reveal that simple counting Clar formulas alone are insufficient to fully understand the electronic and magnetic properties of graphene-related materials, and more attention should be given to such "perturbation" effects.