Abstract
The inherent tendency of BR fragments to undergo coupling is utilized to predict M(2)B(10)H(10) and M(2)@B(10)H(8) complexes (where M = Mn and Fe). Electronic structure analysis of Mn(2)B(10)H(10) (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 Fe(2)@B(10)H(10) (8) stabilize a twisted [10]boraannulene structure. The removal of 2H from 7 and 8 leads to the planar structures Mn(2)@B(10)H(8) (11) and Fe(2)@B(10)H(8) (10), respectively. The stability of the planar arrangements is due to multicentered (σ + π) bonding, where π-donation occurs from the M(2) (M = Fe and Mn) unit to the borocyclic unit. The presence of 10π electrons in M(2)@B(10)H(8) 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 FeB(5) and Fe(2)B(5), considering Fe(2)@B(10) as the building block, bringing this molecular boron chemistry into the solid state. One of the predicted monolayers, β-Fe(2)B(5), 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.