Iron-Iridium Mixed-Metal Carbonyl Clusters. 4. Synthesis, Characterization, and Chemical Behavior of [FeIr4(CO)13]2- and [Fe2Ir4(CO)16]2-. Solid-state Structures of [PPh4]2[FeIr4(CO)13] and [NEt4][NMe3(CH2Ph)][Fe2Ir4(CO16)]

The cluster [FeIr4(CO)13]2− is obtained by decarbonylation of [FeIr4(CO)15]2−, either at room temperature or by moderate heating of a solution of the complex. The salt [PPh4]2[FeIr4(CO)13]·C4H8O crystallizes in the triclinic space group P1̄ (No. 2), with a = 11.337(4) Å = 13.105(4) Å, c = 23.306(6) Å, α = 100.04(2)°, β = 97.99(2)°, γ = 106.68(2)°, V - 3200(4) Å3, and Z = 2. The structure was solved and refined by full-matrix least-squares methods down to R = 0.050 and Rw = 0.053 for 3914 independent reflections with I ≥ 3σ(I). The anion consists of a trigonal bipyramidal metal frame with the iron located in the apical position; the apical and equatorial metal atoms are connected by short bond distances, as commonly observed in bipyramidal clusters having 72 cluster valence electrons. Average metal-metal bond distances (Å): Ireq‒Ireq = 2.748, Irap‒Ireq = 2.735, Feap−Ireq = 2.670. The cluster [Fe2Ir4(CO)16]2− may be obtained by condensation of [Fe2(CO)8]2− or [Fe(CO)4]2− onto Ir4(CO)12. The salt [NEt4][NMe3(CH2Ph)][Fe2Ir4(CO)16] crystallizes in the monoclinic space group P21/c (No. 14), with a = 10.763(2) Å, b = 20.525(3) Å, c = 19.345(3) Å, β = 97.36(1)°, V = 4238(2) Å 3, and Z = 4. The structure was solved and refined by full-matrix least-squares methods down to R = 0.041 and Rw = 0.047 for 3624 independent reflections with I ≥ 3σ(I). The anion consists of an almost regular octahedron of metal atoms, adopting a ligand architecture with four asymmetric face-bridging and twelve terminal carbonyl ligands. From the X-ray data the isomer with the iron atoms trans to each other was found to be prevalent (>80%), but the exact ratio between the cis and trans isomers could not be evaluated. The cluster ideally belongs to the S4 point group of symmetry. The average metal-metal distance is 2.747 Å. © 1993, American Chemical Society. All rights reserved.