화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.122, No.30, 6196-6205, 2018
Boron Teetotum: Metallic [Ti(B6CxNy)](q) and Bimetallic [Ti-2(B6CxNy)](q) Nine-Membered Heterocycles with x plus 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 B9(-) and B9(3-) and C and N isoelectronic derivatives where perfectly planar B6N3, B6CN2, B6C2N, and B6C3 heterorings are coordinated with one and two Ti atoms. The presence of both C and N atoms induces bimetallic heterocycles while Ti2B9q 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-2 with different eigenstates of B6CxNy 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 sigma and pi 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 sigma and pi electron systems.