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

In the present theoretical study using DFT computations, we successfully designed a series of boron clusters possessing a teetotum shape stabilized upon metal doping. The resulting M2B18 teetotum geometry emerges as a general structural motif for the B-18 boron cluster doped by either two 4d and 5d transition metal atoms. Doping of two different metal atoms also conserves the teetotum motif such as in the mixed RhPdB18+ and RhPdB18+ clusters. A bonding analysis points out that each dimeric metal unit enjoys several stabilizing orbital interactions with an idealized B-18 tubular moiety and thereby establish a bimetallic configuration of [sigma(sigma(5s)-B-18)](2) [pi(pi(4d)-B-18)](4) [sigma(sigma(4d)-B-18)](2) [delta(delta(4d)-B-18)](4) [sigma*(sigma(4d)-B-18)](2) [pi*(4d)](4) [sigma(sigma*(4d)-B-18)](2) [delta*(4d)](4) for 4d metals and of [sigma(sigma(6s)-B-18)](2) [pi(pi(5d)-B-18)](4) [sigma(sigma(5d)-B-18)](2) [delta(delta(5d)-B-18)](4) [sigma*(sigma(5d)-B-18)](2) [pi*(5d)](4) [sigma(sigma*(5d)-B-18)](2) [delta*(5d)](4) for 5d metal atoms for 24 electrons. All the M2B18q teetotum structures considered behave as aromatic compounds whose character is indicated by the strongly diatropic current density.