Stabilization of High Oxidation States in Transition Metals. 2.1 WCl6 Oxidizes [WF6]-, but Would PtCl6 Oxidize [PtF6]-? An Electrochemical and Computational Study of 5d Transition Metal Halides: [MF6]z versus [MCl6]z (M = Ta to Pt; z = 0, 1−, 2−)

The trends in redox potentials for isovalent series of 5d hexafluoro- and -chlorometalates, [MX6]0/- and [MX6]-/2- (M = Ta to Pt; X = F, Cl), are compared, including the previously unpublished electrochemistry of [IrF6]2-. For a given series, the trend in redox data can be understood in terms of the core charge of the metal and interelectronic terms. However, there is a marked convergence of the electrochemical redox potentials for isovalent series of [MF6]z/z-1 and [MCl6]z/z-1 (z = 0, 1−) complexes. Thus, while the oxidation potential of [TaF6]2- is 1.6 V lower than that of [TaCl6]2-, the oxidation potential of [IrF6]2- is only 0.5 V lower than that of [IrCl6]2-. The redox data correlate well with computed electron affinities of MX6 and [MX6]- derived from density functional calculations. A fragmentation approach is adopted to analyze the electrochemical trends in terms of the properties of the metal center and trends in the metal−halide bonding. The observed convergence in redox data for isovalent [MX6]...