The coloring problem in the solid-state metal boride carbide ScB2C2: a theoretical analysis

The electronic properties of the layered ternary metal boride carbide ScB2C2, the structure of which consists of B/C layers made of fused five- and seven-membered rings alternating with scandium sheets, are analyzed. In particular, the resp. positions of the B and C atoms (the so-called coloring problem) are tackled using d. functional theory, quantum theory of atoms in mols., and electron localizability indicator calcns. Results reveal that (i) the most stable coloring minimizes the no. of B-B and C-C contacts and maximizes the no. of boron atoms in the heptagons, (ii) the compd. is metallic in character, and (iii) rather important covalent bonding occurs between the metallic sheets and the boron-carbon network.