Synthesis, Molecular Structure, and Vibrational Spectra of mer-Tris(carbonyl)iridium(III) Fluorosulfate, mer-Ir(CO)3(SO3F)3

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Abstract
Addition of carbon monoxide (0.5−2 atm) to iridium(III) fluorosulfate, Ir(SO3F)3, dissolved in HSO3F over 4 days and at 60 °C, results in the quantitative formation of tris(carbonyl)iridium(III) fluorosulfate Ir(CO)3(SO3F)3. Slow evaporation of the solvent produces single crystals of mer-Ir(CO)3(SO3F)3. Crystal structure data for mer-Ir(CO)3(SO3F)3: monoclinic, space group P21/c, Z = 4, a = 8.476(1) Å, b = 12.868(2) Å, c = 12.588 (1) Å, β = 108.24(1)°, V = 1304.0 Å3, T = 200 K, RF = 0.022 for 2090 data (Io ≥ 2.5σ(Io)) and 200 variables. Vibrational spectra of the crystalline solid are consistent with a mer-isomer with CO stretching modes at 2249 (A1), 2208 (B1), and 2198 (A1) cm-1 in the IR spectrum. In solution of HSO3F, additional CO stretching bands attributed to the fac-isomer are found in the FT-Raman and IR spectra at 2233 (A1) and 2157 cm-1 (E). Additional evidence for a mixture of fac- and mer-isomers comes from 19F NMR spectra. The vibrational spectra suggest strongly reduced iridium to CO π-back-bonding. The crystal structure reveals significant intra- and intermolecular contacts between the electropositive C atom of the CO groups and O or F atoms of the fluorosulfate groups. Hence mer-tris(carbonyl)iridium(III) fluorosulfate becomes the first thermally stable, structurally characterized, and predominantly σ-bonded carbonyl derivative of a metal in the +3 oxidation state.

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