Structure and bonding of IrB12−: converting a rigid boron B12 platelet to a Wankel motor

Abstract

The global minimum of IrB₁₂⁻ is a C_3v symmetric bowl-like structure in which the Ir atom is located on the concave side of the bowl, similar to its lighter congeners, CoB₁₂⁻ and RhB₁₂⁻ clusters. Although all these MB₁₂⁻ (M = Co, Rh, Ir) clusters show dynamical behaviour, analogous to that of the so-called ‘Wankel motors’, the energy barrier for the rotation of the inner B₃ ring within the peripheral B₉ ring is the lowest in the IrB₁₂⁻ case (5.0 kcal mol⁻¹ only). The geometrical feature along with the lower interaction energy between B₃ and MB₉ moieties are responsible for a smaller rotational energy barrier in IrB₁₂⁻ than those in CoB₁₂⁻ and RhB₁₂⁻ clusters.