From a Möbius-aromatic interlocked Mn2B10H10 wheel to the metal-doped boranaphthalenes M2@B10H8 and M2B5 2D-sheets (M = Mn and Fe): a molecules to materials continuum using DFT studies

Abstract

The inherent tendency of BR fragments to undergo coupling is utilized to predict M₂B₁₀H₁₀ and M₂@B₁₀H₈ complexes (where M = Mn and Fe). Electronic structure analysis of Mn₂B₁₀H₁₀ (7) shows that the metal d-orbitals stabilize the interlocked boron wheel structure, forming an unprecedented geometrical pattern with Möbius aromaticity. The two additional electrons in Fe₂@B₁₀H₁₀ (8) stabilize a twisted [10]boraannulene structure. The removal of 2H from 7 and 8 leads to the planar structures Mn₂@B₁₀H₈ (11) and Fe₂@B₁₀H₈ (10), respectively. The stability of the planar arrangements is due to multicentered (σ + π) bonding, where π-donation occurs from the M₂ (M = Fe and Mn) unit to the borocyclic unit. The presence of 10π electrons in M₂@B₁₀H₈ relates it to naphthalene, having Hückel π-aromaticity. The condensation of naphthalene to graphene in two dimensions suggests the ability to build the different metal boride monolayers FeB₅ and Fe₂B₅, considering Fe₂@B₁₀ as the building block, bringing this molecular boron chemistry into the solid state. One of the predicted monolayers, β-Fe₂B₅, is found to be the global minimum in the planar arrangement based on a USPEX crystal structure search algorithm. Electronic structure analysis further shows that the stabilization mechanism in the molecular building block remains unaltered in the solid state.