Infrared Spectra and Quantum Chemical Calculations of the Bridge-Bonded HC(F)LnF2 (Ln = La–Lu) Complexes

Lanthanide metal atoms, produced by laser ablation, were condensed with CHF 3 (CDF 3 ) in excess argon or neon at 4 K, and new infrared absorptions are assigned to the oxidative addition product fluoromethylene lanthanide difluoride complex on the basis of deuterium substitution and density functional theory frequency calculations. Two dominant bands in the 500 cm –1 region are identified as metal–fluorine stretching modes. A band in the mid-600 cm –1 region is diagnostic for the unusual fluorine bridge bond C–(F)–Ln. Our calculations show that most of the bridged HC(F)LnF 2 structures are 3–6 kcal/mol lower in energy than the open CHF-LnF 2 structures, which is in contrast to the open structures observed for the corresponding CH 2 -LnF 2 methylene lanthanide difluorides. Argon-to-neon matrix shifts are 15–16 cm –1 to the blue for stretching of the almost purely ionic Ln–F bonds, as expected, but 10 cm –1 to the red for the bridge C–(F)–Ln stretching mode, which arises because Ar binds more strongly to the electropositive Ln center, decreasing the bridge bonding, and thus allowing a higher C–F stretching frequency.