Investigation of Isolated IrF5−, IrF6− Anions and M[IrF6] (M = Na, K, Rb, Cs) Ion Pairs by Matrix‐Isolation Spectroscopy and Relativistic Quantum‐Chemical Calculations

The molecular IrF5−, IrF6− anions and M[IrF6] (M = Na‐Cs) ion pairs were prepared by co‐deposition of laser‐ablated MF with IrF6 and isolated in solid Ne or Ar matrices. The free anions were obtained by co‐deposition of IrF6 with laser‐ablated metals (Ir, Pt) as electron sources. The products were characterized in a combined analysis of matrix IR spectroscopy and electronic structure calculations using two‐component quasi‐relativistic DFT methods accounting for scalar‐relativistic and spin‐orbit coupling effects as well as multi‐reference configuration‐interaction approaches with SOC. Inclusion of SOC is crucial in the prediction of spectra and properties of IrF6− and its alkali‐metal ion pairs. The observed IR bands and the computations show that the IrF6− anion adopts an Oh structure in a nondegenerate ground state stabilized by SOC effects, and not a distorted D4h structure in a triplet ground state as suggested by scalar‐relativistic calculations. The corresponding “closed‐shell” M[IrF6] ion pairs with C3v symmetry are stabilized by coordination of an alkali metal ion to three F atoms, and their structural change in the series from M = Na to Cs was proven spectroscopically. There is no evidence for the formation of IrF7, IrF7− or M[IrF7] (M = Na‐Cs) ion pairs in our experiments.