[C₆F₅Xe]⁺ and [C₆F₅XeNCCH₃]⁺ Salts of the Weakly Coordinating Borate Anions, [BY₄]⁻ (Y = CN, CF₃, or C₆F₅)

New examples of [C6F5Xe]+ salts of the weakly coordinating [BY4]− (Y = CN, CF3, or C6F5) anions were synthesized by metathesis of [C6F5Xe][BF4] with MI[BY4] (MI = K or Cs; Y = CN, CF3, or C6F5) in CH3CN at −40 °C, and were crystallized from CH2Cl2 or from a CH2Cl2/CH3CN solvent mixture. The low-temperature (−173 °C) X-ray crystal structures of the [C6F5Xe]+ cation and of the [C6F5XeNCCH3]+ adduct-cation are reported for [C6F5Xe][B(CF3)4], [C6F5XeNCCH3][B(CF3)4], [C6F5Xe][B(CN)4], and [C6F5XeNCCH3][B(C6F5)4]. The [C6F5Xe]+ cation, in each structure, interacts with either the anion or the solvent, with the weakest cation–anion interactions occurring for the [B(CF3)4]− anion. The solid-state Raman spectra of the [C6F5Xe]+ and [C6F5XeNCCH3]+ salts have been assigned with the aid of electronic structure calculations. Gas-phase thermodynamic calculations show that the donor–acceptor bond dissociation energy of [C6F5XeNCCH3]+ is approximately half that of [FXeNCCH3]+. Coordination of CH3CN to [C6F5Xe]+ is correlated with changes in the partial charges on mainly Xe, the ipso-C, and N, that is, the partial charge on Xe increases and those on the ipso-C and N decrease upon coordination, typifying a transition from a 2c–2e to a 3c–4e bond.