Darstellung und Schwingungsspektren von Chloro-Bromo-Platinaten(IV) einschließlich der Stereoisomeren / Preparation and Vibrational Spectra of Chloro-Bromo-Platinates(IV) Including Stereoisomers

Abstract

The mixed chloro-bromo complexes [PtClnBr6-n]2-, n = 1-5, are separated by ion exchange chromatography on diethylaminoethylcellulose. The separation of corresponding stereoisomers for n = 2, 3, 4 is not possible. Due to the stronger trans-effect of Br compared with Cl, on treatment of [PtBrß]2- with Cl- in the presence of Br2 nearly pure cis-isomers, and by reaction of [PtClsBr]2- and cis-fPtC^Bro]2- with Br~/Br2 completely pure transisomers are formed. The stereoselectivity of the successive ligand exchange reactions is better than in corresponding series of Re, Os and Ir. The highly resolved vibrational spectra allow the distinction of the mixed ligand complexes as well as the estimation of purity of the isomers. All allowed stretching frequencies are observed and assigned according to point groups D4h, C4V, C3V and C2V. Especially in the ν(Pt-Br) region it is possible to distinguish bands arising either from symmetric Br-Pt-Br or asymmetric Cl-Pt-Br axes. The UV/VIS spectra exhibit systematic hypsochromic shifts on the successive exchange of Br-ligands by Cl. A critical discussion of the literature concerning chloro-bromo-platinates- (IV) shows the importance of effective separation processes for the isolation of pure mixed ligand complexes