Infrared and DFT Investigations of the XC⋮ReX<sub>3</sub> and HC⋮ReX<sub>3</sub> Complexes:  Jahn−Teller Distortion and the Methylidyne C−X(H) Stretching Absorptions

The XC⋮ReX<sub>3</sub> complexes (X = F, Cl) are produced by CX<sub>4</sub> reaction with laser-ablated Re atoms, following oxidative C−X insertion and α-halogen migration in favor of the carbon−metal triple bond and are identified through the observation of characteristic absorptions in the argon matrix infrared spectra and comparison with vibrational frequencies calculated by density functional theory. The methylidyne C−F and C−Cl stretching absorptions are observed near 1584 and 1328 cm<sup>-1</sup>, and the C−H stretching modes for HC⋮ReX<sub>3</sub> at 3104 and 3097 cm<sup>-1</sup>, respectively, which are substantially higher than the precursor stretching modes and in agreement with the general trend that higher s-orbital character in carbon hybridization leads to a higher stretching frequency. The Jahn−Teller effect in the doublet-state XC⋮ReX<sub>3</sub> and HC⋮ReX<sub>3</sub> complexes gives rise to distorted structures with <i>C</i><i><sub>s</sub></i> symmetry and two equivalent longer Re−X bonds and one slightly shorter Re−X bond.