Double aromaticity in transition metal centered double-ring boron clusters M@B2n (M = Ti, Cr, Fe, Ni, Zn; n = 6, 7, 8)

Abstract

It is well known that double-ring boron clusters have got the special double aromaticity with delocalized π orbitals in two directions (tangential and radial), which are potential ligands centered by a transition metal. In this article, the transition metal centered double-ring boron clusters M@B2n (M = Ti, Cr, Fe, Ni, Zn; n = 6, 7, 8) are theoretically investigated by density functional theory calculations. These endohedral compounds have also got double aromaticity in both tangential and radial directions. Interestingly, the tangential delocalized π orbitals of boron ligands following the Huckle's (4n + 2) rule do not interact with the central metal, while the radial π orbitals of boron ligands are bonded with the central mental to form spd-π endohedral bonding. The spd-π endohedral bonding follows the 18e-principle in Ni@B14 and Fe@B16. However, due to the flat shape of the compounds, 14e (Cr@B14) and 16e (Ni@B12) can also be electronically very stable where the energy levels of the spd-π orbitals delocalized in z-direction rise up. This intriguing bonding model makes sense in further study of the boron chemistry.

Cobalt-centred boron molecular drums with the highest coordination number in the CoB16− cluster

“…1 ) appears to be the most stable one out of all other quintet isomers. It should be mentioned that there were two previous DFT calculations on similar drum-like structures of neutral boron clusters doped with transition metal atoms 24 25 .…”

Manganese-centered tubular boron cluster – MnB16−: A new class of transition-metal molecules

“…24 Metal-doped boron clusters have been investigated computationally. [25][26][27] Very recently, a cobalt-doped boron cluster CoB 16 − was observed experimentally and characterized using photoelectron spectroscopy (PES) and ab initio calculations. 28 It was found to possess a Co-centered drum or tubular structure with two B 8 rings sandwiching the Co atom.…”

“Bottled” spiro-doubly aromatic trinuclear [Pd2Ru]+complexes

“…Indeed, as we will see later, Ru is a full participant of benzene π-cloud while not being a structural part six-membered carbon ring. Double aromatic species have been a topic of perpetual endeavors both in computational design [35][36][37][38][39][40][41] and photoelectron spectroscopy experiments yielding novel but "non-bottled" short living clusters. [42][43][44][45] However, to the best of our knowledge, none were obtained as stable phases in the bulk except Saito's one.…”