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].C4H8O AND [NET4][NME3(CH2PH)][FE2IR4(CO)16]

The cluster [FeIr4(CO)13]2- is obtained by decarbonylation of [FeIr4(C O)15]2-, either at room temperature or by moderate heating of a soluti on of the complex. The salt [PPh4]2[FeIr4(CO)13].C4H8O crystallizes in the triclinic space group P1BAR (No. 2), with a = 11.337(4) angstrom, b = 13.105(4) angstrom, c = 23.306(6) angstrom, alpha = 100.04(2)-deg rees, beta = 97.99(2)-degrees, gamma = 106.68(2)-degrees, V = 3200(4) angstrom3, and Z = 2. The structure was solved and refined by full-mat rix least-squares methods down to R = 0.050 and R(w) = 0.053 for 3914 independent reflections with I greater-than-or-equal-to 3sigma(I). The anion consists of a trigonal bipyramidal metal frame with the iron lo cated in the apical position; the apical and equatorial metal atoms ar e connected by short bond distances, as commonly observed in bipyramid al clusters having 72 cluster valence electrons. Average metal-metal b ond distances (angstrom): Ir(eq)-Ir(eq) = 2.748, Ir(ap)-Ir(eq) = 2.735 , Fe(ap)-Ir(eq) = 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 sal t [NEt4][NMe3(CH2Ph)][Fe2Ir4(CO)16] crystallizes in the monoclinic spa ce group P2(1)/c (No. 14), with a = 10.763(2) angstrom, b = 20.525(3) angstrom, c = 19.345(3) angstrom, beta = 97.36(1)-degrees, V = 4238(2) angstrom3, and Z = 4. The structure was solved and refined by full-ma trix least-squares methods down to R = 0.041 and R(w) = 0.047 for 3624 independent reflections with I greater-than-or-equal-to 3sigma(I). Th e anion consists of an almost regular octahedron of metal atoms, adopt ing a ligand architecture with four asymmetric face-bridging and twelv e terminal carbonyl ligands. From the X-ray data the isomer with the i ron atoms trans to each other was found to be prevalent (>80%), but th e exact ratio between the cis and trans isomers could not be evaluated . The cluster ideally belongs to the S4 point group of symmetry. The a verage metal-metal distance is 2.747 angstrom.