Darstellung und Charakterisierung der Chloro-Bromo-Iridate(III) und -(IV) einschließlich der Stereoisomeren / Preparation and Characterisation of Chloro-Bromo-Iridates(III) and -(IV) Including Stereoisomers

The mixed chloro-bromo complexes [IrClnBr6-n]2- and [IrClnBr6-n]3-, n = 1 - 5. were separated by ion exchange chromatography on diethylaminoethylcellulose. Due to the stronger trans-effect of Br compared with Cl, on treatment of [IrBr6]2- 3- with Cl- nearly pure cis/fac-isomers and by reaction of [IrCl6]2,3- with Br- trans/mer-isomers for n = 2,3,4 were formed. The stereoselectivi­ty of successive ligand exchange reactions is better for the Ir(III) than for the Ir(IV) system. The diamagnetic Ir(III) and the paramagnetic Ir(IV) complexes can be interconverted reversibly by redox reactions at low temperature. As shown by cyclic voltammetric measurements, the redox potentials within the series [IrClnBr6-n]2- 3- are linearly dependent on n. In aqueous solution the normal potentials are in the range of Eo = 0.838 V ([IrBr6]2-,3-) to Eo = 0.908 V ([IrCl6]2-,3-). The vibrational spectra of the mixed ligand complexes are assigned according to point groups D4h, C4v, C3v and C2v. They are similar for corresponding chloro-bromo-iridates, but distinguished by a shift of 10-25 cm-1 to higher wave numbers for most of the stretching vibrations going from Ir(III) to Ir(IV).