Photodetachment Dynamics and Structural Flexibility of Undercoordinated Iridium Halides IrCl_n⁻ (n = 3−5): An Experimental and Theoretical Investigation

Three undercoordinated iridium chloride anions, IrCl_n⁻ (n = 3–5), and their neutral counterparts were investigated by cryogenic anion photoelectron spectroscopy and theoretical calculations. Photodetachment of IrCl_n⁻ leads to the formation of the corresponding neutral complex, i.e., a triplet ground state for n = 3, a quartet for n = 4, and close-lying singlet and triplet for n = 5. The vertical detachment energies are determined to be 3.89, 4.98, and 5.14 eV for n = 3, 4, and 5, respectively, revealing superhalogen anion properties with increasing electron detachment energies as chloride ligands added. The IrCl₃⁻ spectrum features an extremely broad, lowest electron binding energy band, attributed to resonant autodetachment with prominent non-Franck–Condon profiles. In IrCl₅⁻, detachment prompts a d-orbital rearrangement that drives a structural transformation from a twisted square-based pyramidal to a trigonal–bipyramidal geometry in the singlet state. These findings provide insights into the electronic and structural adaptability of iridium halides, advancing our understanding of ligand exchange reactions and dissociative stability in transition metal complexes.