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ChemInform Abstract The reaction of (PtCl6)2-with BrF3 yields the mixed complexes (PtFnCl6-n)2-with n = 1-5; the product distribution depends on the reaction temp. and time. The complexes with n = 2, 3, 4 have cis-configuration. Due to the stronger trans-effect of Cl compared to F, trans-isomers can be generated stereospecifically by treatment of (PtF5Cl)2-and cis-(PtF4Cl2)2-with Cl-. The vibrational spectra of the mixed complexes are completely assigned according to the point groups D4h (trans-isomers with n = 2, 4), C4v (n = 1, 5), C3v (cis-isomer, n = 3), and C2v (cis-isomers, n = 2, 4; and trans-isomer, n = 3).

The electronic absorption spectra of the solid tetraalkylammonium salts of [OsF"Cl6_"]2-, n = 0 -6 , including the stereoisomers for n = 2, 3, 4, are measured at 10 K. The strong bands in the UV/VIS region are assigned to charge-transfer transitions from 7r(t] u, t2u) and a ( t)u) Cl orbitals into the tc (tfg) Os(IV) level. The observed splittings and shifts are interpreted by qualitative MO treatment according to point groups D 4h, C4v, C 3v and C2v of the mixed complexes. The weak intraconfigurational transitions within the t^g configuration of Os(IV) are splitted by spin orbit coupling and lowered symmetry into multiplets with up to five states, observed in the NIR regions4700-7300, 10 700-13 200 and 17 000-21 600 cm-1. The O -Otransitions are deduced from vibrational fine structure; in some cases they are confirmed by electronic Raman bands with the same frequencies and by hot bands observed in the normal temperature spectra. Within the series of complexes all absorption bands are shifted systemat ically to higher energies with increasing number of F-ligands. Einleitung

AbstractThe stepwise replacement of ligands in [OsCl6]2- by oxidation with BrF3 generates the mixed complexes [OsFnCl6-n]2-, n = 1 - 5, of which the species with n = 2,3,4 are cw-configurated. Due to the stronger trans-effect of Cl compared to F on treatment of [OsF5Cl]2- and cis-[OsF4Cl2]2- with Cl- the trans-isomers are formed stereospecifically. The pure fluoro-chloro-osmates(IV) are separated by ion exchange chromatography on diethylaminoethylcellulose. From the pairs of stereoisomers the cis-compounds are always first eluted, whereas the trans-complexes are moving faster in an electric field by 3 to 5% . The vibrational spectra of octahedral mixed ligand complexes are generally discussed according to point groups Oh, D4h, C4v, C3v and C2v. For the fluoro-chloroosmates(IV) all stretching and deformation bands are assigned. They are observed in the characteristic regions; ν(OsF): 625-490 > ν(OsCl): 360-300 > δ (FOsF): 275-210 > δ (FOsCl) > δ (ClOsCl): 190-150 > νL: < 100 cm -1.

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