WEAKLY COORDINATING ANIONS

Our fluorine chemistry research has also contributed to the chemistry and bonding of groups having electronegativities approaching that of fluorine such as the OIOF₄^- and F₅TeO-groups. The OIOF₄^- and F₅TeO- groups have been shown to be among the most electronegative groups known. Examples of noble-gas derivatives of both ligand groups have been synthesized and characterized. Contributions to the F₅TeO-derivative chemistry of other main-group and transition metal elements have also been made. Particularly noteworthy examples are the syntheses of the weakly coordinating and oxidatively resistant pnicogen anion series, M(OTeF₅)₆^-; (M = As, Sb, Bi). They have been exploited to stabilize the novel SbBr₄⁺ cation as well as the AsBr₄⁺ cation and have been used by other workers to stabilize cation-solvent interactions in the solid state. A dramatic illustration of the utility of these anions is the recent syntheses and structural characterizations of room-temperature stable carbocations derived from CFCs (chlorofluorocarbons) and other tetrahalomethanes by oxidation of a halogen ligand (other than fluorine) with XeOTeF₅⁺Sb(OTeF₅)₆^-. The stable carbocations CFCl₂⁺, CFClOTeF₅⁺, CCl₃⁺, CFBr₂⁺, CBr₃⁺, CBr(OTeF₅)₂⁺ and C(OTeF₅)₃⁺ have thus far been obtained as Sb(OTeF₅)₆^-; salts and characterized by X-ray crystal structure determinations and/or spectroscopically. The CCl₃⁺, CBr₃⁺ and C(OTeF₅)₃⁺ salts are stable at room temperature.