Synthese und spektroskopische Charakterisierung von Fluorocarbonylosmaten sowie Normalkoordinatenanalyse und Kristallstruktur von fac-[OsF3Br2(CO)]2–

Synthesis and Spectroscopic Characterization of Fluorocarbonylosmates, Normal Coordinate Analysis and Crystal Structure of fac -[OsF₃Br₂(CO)]^2– By treatment of (n-Bu₄N)₂[OsBr₅(CO)] with TlF in C₆H₅CF₃ fac-(n-Bu₄N)₂[OsF₃Br₂(CO)] is formed, from which salts with the cations (Et₄N)⁺, (py₂CH₂)²⁺, Tl⁺ and Cs⁺ are obtainable. Oxidation of the by-product [OsF₅(CO)]^2– with Cl₂ yields [OsF₅(CO)]^– which ¹⁹F NMR spectrum reveals a quintet (δ_F = 89.9) and a dublet (43.5 ppm) in the ratio 1 : 4 with coupling constants ²J_FF = 94.9 Hz. Simultaneously produced mer-[OsF₃Cl₂(CO)]^– exhibits in the high field region a triplet (δ_F = –70.4) and a dublet (–66.2 ppm) in the ratio 1 : 2 and ²J_FF = 9.5 Hz. The X-ray structure determinations of fac-Tl₂[OsF₃Br₂(CO)] ( 1 ) (monoclinic P2₁/n, a = 11.143(12), b = 11.654(4), c = 13.751(10) Å, β = 91.50(6)°, Z = 8) and fac-(py₂CH₂)[OsF₃Br₂(CO)] · 1/2(CH₃)₂CO ( 2 ) (triclinic, P 1, a = 8.432(1), b = 9.009(1), c = 12.402(2) Å, α = 80.30(1), β = 79.68(2), γ = 68.14(1)°, Z = 2) result in nearly C_s symmetry of the complex anion with bond lengths in the ranges Os–F = 1.98–2.08, Os–Br = 2.45–2.46, Os–C = 1.83–1.84, C–O = 1.10 – 1.17 Å. Using the molecular parameters of the X-ray determinations the IR spectra have been assigned by normal coordinate analysis. The valence force constants are f_d(CO) = 15.4–15.7, f_d(OsC) = 4.4–4.7, f_d(OsF) = 2.4–2.7, f_d(OsF˙) = 1.6–2.0, f_d(OsBr) = 1.7–2.1 mdyn/Å.