High‐Resolution Photoelectron Imaging of IrB₃⁻: Observation of a π‐Aromatic B₃⁺ Ring Coordinated to a Transition Metal

Abstract

In a high-resolution photoelectron imaging and theoretical study of the IrB₃ ^- cluster, two isomers were observed experimentally with electron affinities (EAs) of 1.3147(8) and 1.937(4) eV. Quantum calculations revealed two nearly degenerate isomers competing for the global minimum, both with a B₃ ring coordinated with the Ir atom. The isomer with the higher EA consists of a B₃ ring with a bridge-bonded Ir atom (C_s , ² A'), and the second isomer features a tetrahedral structure (C_3v , ² A₁ ). The neutral tetrahedral structure was predicted to be considerably more stable than all other isomers. Chemical bonding analysis showed that the neutral C_3v isomer involves significant covalent Ir-B bonding and weak ionic bonding with charge transfer from B₃ to Ir, and can be viewed as an Ir-(η³ -B₃ ⁺ ) complex. This study provides the first example of a boron-to-metal charge-transfer complex and evidence of a π-aromatic B₃ ⁺ ring coordinated to a transition metal.