Aromaticity of Bare Iridium Trimers and Ir3M0/+ and $$\rm{Ir}_3M_2^{+/3+}$$ I r 3 M 2 + / 3 + (M = Li, Na, K, and Be, Ca) Bimetallic Clusters

Abstract

The structural stabilities, bonding nature, electronic properties, and aromaticity of bare iridium trimers $$\rm{Ir}_3^{+/-}$$ with different geometries and spin multiplicities are studied at the DFT/B3LYP level of theory. The ground state of the $$\rm{Ir}_3^{+}$$ cation is found to be the 3A2 (C2v) triplet state and the ground state of the $$\rm{Ir}_3^{-}$$ anion the 5A2 (C2v) quintet state. A detailed molecular orbital (MO) analysis indicates that the ground-state $$\rm{Ir}_3^{+}$$ ion (C2v, 3A2) possesses double (σ and partial δ) aromaticity as well as the ground-state $$\rm{Ir}_3^{-}$$ ion (C2v, 5A2). The multiple d-orbital aromaticity is responsible for the totally delocalized three-center metal-metal bond of the triangular Ir3 framework. $$\rm{Ir}_3^{-}$$ (C2v, 1A1) structure motif is perfectly preserved in pyramidal Ir3M0/+ (Cs, 1A′) and bipyramidal $$\rm{Ir}_3M_2^{+/3+}$$ (C2v, 1A1) (M = Li, Na, K and Be, Ca) bimetallic clusters which also possess the corresponding d-orbital aromatic characters.