Boron Teetotum: Metallic [Ti(BC N )] and Bimetallic [Ti(BC N )] Nine-Membered Heterocycles with x + y = 3 and -1 ≤ q ≤ 3.

We investigated the geometry, stability, and aromaticity of a series of singly and doubly titanium-doped boron clusters. Ti dopants bring in planar cyclic form with a nine-membered boron ring B and B and C and N isoelectronic derivatives where perfectly planar BN, BCN, BCN, and BC heterorings are coordinated with one and two Ti atoms. The presence of both C and N atoms induces bimetallic heterocycles while TiB clusters are not stable in cyclic form. Doubly Ti doped clusters have the shape of a teetotum toy. High thermodynamic stability of these bimetallic boron heterocycles, that are global equilibrium structures of corresponding systems, can be understood as the result of a stabilizing overlap between bonding and antibonding MOs of Ti with different eigenstates of BC N cycles. Both C and N elements, which are more electronegative than the B atom, also enjoy the formation of planar nine-membered ring via classical 2c-2e bonding, rather than occupancy of high coordination position. A double aromaticity feature which comprises both σ and π aromaticity is supported by magnetic responses of electron density within a planar cycle. Such an aromatic character is also in line with the classical electron count for both sets of delocalized σ and π electron systems.