Boron Teetotum: Metallic [Ti(B₆C_xN_y)]^q and Bimetallic [Ti₂(B₆C_xN_y)]^q Nine-Membered Heterocycles with x + y = 3 and −1 ≤ q ≤ 3

Abstract

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.

Formation of the M2B18q Teetotum Boron Clusters with 4d and 5d Transition Metals M = Rh, Pd, Ir, and Pt

“…The present theoretical study allows us to design some new stabilized tubular blocks that are named as teetotum, from the B 18 host. 20,24…”

“…These metal dopants are selected due to the existence of the Rh 2 B 18 and Ni 2 B 22 double ring structures. , As both Pd and Pt elements belong to the same group with Ni, and Ir to the same group with Rh, it can be expected that a doping these isovalent atoms can also generate the stable DR tubular structures. The present theoretical study allows us to design some new stabilized tubular blocks that are named as teetotum , from the B 18 host. , …”

Aromatic character of Oh‐C24N24. A cavernous nitride fullerene bearing N4‐macrocycle motifs

“…Recently, Srinivasu and Ghosh conceived another interesting cavernous structure based on a heteroatomic cage given by O h ‐C 24 N 24 . Such structure exhibits six N 4 ‐macrocyclic faces resembling porphyrin‐like species, and eight 1,3,5‐triazine units at each vertex of the octahedral cage, resulting in a 48‐ π electrons system, where boron clusters and fullerenes exhibit interesting aromatic properties . In last years, the aromatic, nonaromatic, and antiaromatic properties of planar N 4 ‐macrocycles have been well discussed by Fliegl and Sundholm, among other authors, highlighting the capabilities of sustaining extended ring currents under an applied magnetic field.…”

Electronic Structure and Properties of Silicon-Doped Boron Clusters BnSi withn= 15–24 and Their Anions

“…Doping of two transition metal atoms to boron clusters reveals a novel type of hypercoordinated structure, named as bimetallic boron cycles, or teetotum clusters. , Their high thermodynamic stability arises from a combination of two stabilizing effects: on the one hand, each dimeric metal M 2 delivers its electrons to fill the empty levels of the B n string, and on the other hand, both antibonding and bonding MOs of M 2 are significantly stabilized through orbital interactions with the cyclic B n counterpart. The abundance of teetotum clusters leads to the emergence of a rich family of superatoms.…”