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−)

Abstract

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and -chlorometalates, [MX6]0/- and [MX6]-/2- (M = Ta to Pt; X = F, Cl), are compared, including the previously unpublished electrochemistry of [IrF6]2-.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] z / z -1 (x = F, Cl; z = 0, 1−) series is rationalized in terms of the ability of the halide arrays to stabilize the two metal oxidation states involved. The ability of the chloride array to stabilize the higher metal oxidation state increases more rapidly along the third row transition metals than does that of the fluoride array. This counteracts the effects of metal core charge to produce the observed convergence. The computational results indicate that, for the later metals in their highest oxidation states, the redox-active orbital becomes increasingly halide based. In view of this, the stability of the neutral hexahalides with respect to the reductive elimination of X2 was studied, and the results suggest that OsCl6 and IrCl6 are more likely to be stable as novel hexachlorides than PtCl6.

Photodetachment of free hexahalogenometallate doubly charged anions in the gas phase: [ML6]2−, (M=Re, Os, Ir, Pt; L=Cl and Br)

“…For the four chloride anions, there has been a recent calculation by Macgregor and Moock. 51 Table II shows that their calculated EAs are consistent with our measured values and show the same trend ͑also see Fig. 12͒, although the calculations in general underestimated the EAs.…”

“…The latter has been interpreted as arising from effects of interelectronic correlation and repulsion in the theoretical study. 51 An oxidation reaction is a one-electron process and proceeds according to ͓MX 6 ͔ 2Ϫ˜͓ MX 6 ͔ Ϫ ϩe Ϫ , which, beside Ϫ ͑MϭRe, Os, Ir, and…”

“…45 These species are interesting electron transfer agents in solutions and have been extensively studied as such. [46][47][48][49][50][51] There is also an extensive body of literature on the properties of these species in solids. Their ground state electronic energy levels have been investigated in numerous studies of optical absorption, 52 magnetic circular dichroism, 53 and x-ray photoelectron spectroscopy.…”

Die schwer fassbaren Halogenide VCl5, MoCl6 und ReCl6

“…[18] Über die Herstellung von ReCl 6 gibt es widersprüchliche Angaben. [17] Die Fluor-Chlor-Austauschmethode, die wir zur Herstellung des MoCl 6 genutzt haben, wurde auch von anderen schon zur Herstellung von ReCl 6 versucht, [12,13,15] aber offensichtlich wurden nur verunreinigte Produkte erhalten. [13][14][15][16] In jüngerer Zeit wurde berichtet, dass ReCl 6 À elektrochemisch offensichtlich zu ReCl 6 oxidiert werden kann.…”

“…[13][14][15][16] In jüngerer Zeit wurde berichtet, dass ReCl 6 À elektrochemisch offensichtlich zu ReCl 6 oxidiert werden kann. [17] Die Fluor-Chlor-Austauschmethode, die wir zur Herstellung des MoCl 6 genutzt haben, wurde auch von anderen schon zur Herstellung von ReCl 6 versucht, [12,13,15]…”