Darstellung, 19F- und 195Pt-NMR-Spektren, Schwingungsspektren und Normalkoordinatenanalyse von Fluoro-Chloro-Bromo-Platinaten(IV) / Preparation, 19F and 195Pt NMR Spectra, Vibrational Spectra and Normal Coordinate Analysis of Fluoro-Chloro-Bromo-Platinates(IV)

Abstract

By stereoselective ligand exchange reactions of [PtF5Cl]2− and cis-[PtF4Cl2]2− with Br− mixtures containing seven different fluoro-chloro-bromo- and two fluoro-bromo-platinates(IV) are formed, from which trans-Cs2[PtF4ClBr] 4t 11 and mer-Cs2[PtF3Clc 2Br] 3m2c 1 have been isolated by ion exchange chromatography on DEAE cellulose. All threefold mixed complexes could be detected by in situ 19F and 195 Pt NMR measurements. Due to the stronger trans influence of Cl in comparison with F on asymmetric F′-Pt-Cl′ axes the F atoms are deshielded and their signals δ(19F) are shifted on the average by 106 ppm to lower field as compared with δ(19F) of symmetric F-Pt-F axes. For the same reason the mean coupling constant 1J(FPt) of 1857 Hz is 44 % higher than 1J( FPt) of 1288 Hz. The substitution of a cis positioned Cl against Br causes shifts of -7,6 ppm for δ(19F) and of -8,4 ppm for δ(19F ). The cis influence on the coupling constants 1J(F P t) and 1J( FPt), on the average 4 Hz, is more than two orders of magnitude smaller than the trans influence. The coupling constants between inequivalent F atoms 2J(FF) amounts to 44 Hz. The mean highfield shift of the l95Pt signals on exchange of one F for Cl is 1177, of one Cl for Br 210 ppm. Due to the increasing trans influence F < Cl < Br on the stretching vibrations of asymmetrically coordinated axes characteristic frequency shifts of up to 15 % are observed. The normal coordinate analyses performed on 4t11 and 3m2c 1 reveal that the force constant fd(PtF) is by 15 % higher than fd(PtF), and that fd(PtCl′) is by 31 % higher than fd(PtCl). Very intense Raman bands at 277 and 267 cm −1 are explained by strong vibrational coupling of the π-deformation with a symmetric valence mode of the Cl -Pt-Br′axis.