Iron-Iridium Mixed-Metal Carbonyl Clusters. 3.2 Synthesis, Chemical Characterization, Electrochemical Behavior, and Solid-State Structures of [NEt4]3[FeIr5(CO)15], [NMe3(CH2Ph)]2[HFeIr5(CO)15], and [NMe3(CH2Ph)][FeIr5(CO)16]. Spectroscopic and Chemical Evidence for the Existence of [HFe3Ir(CO)12]2-, [H2Fe3Ir(CO)12]-, and [H2FeIr5(CO)15]-

The reaction of [HFe(CO)4]- with Ir(CO)3Br (in molar ratio 3:1) produced [HFe3Ir(CO)12]2- (1), which reacts with acids to yield the dihydride complex [H2Fe3Ir(CO)12]- (2). The salt [NEt4]2[HFe3Ir(CO)12] crystallizes in the orthorhombic space group Pnma, with a = 20.346 (7) Å, b = 15.135 (2) Å, c = 11.807 (5) Å, V = 3636 (1) Å3, and Z = 4; a full structural determination was prevented by the poor quality of the crystals. The reaction of [FeIr4(CO)15]2- with [Ir(CO)4]-, in refluxing acetonitrile, has yielded the new compound [FeIr5(CO)15]3- (3). The trianion reacts with stoichiometric amount of H+ to form [HFeIr5(CO)15]2- (4) and with acids in excess to yield the corresponding dihydride derivative [H2FeIr5(CO)15]- (5), which, at room temperature, is not stable and is readily transformed into [FeIr5(CO)16]- (6). The salts of 3, 4, and 6 were characterized by single-crystal X-ray analyses. [NEt4]3[FeIr5(CO)15] crystallizes in the triclinic space group [formula omited], with a = 18.827 (5) Å, b = 19.476 (6) Å, c = 18.064 (5) Å, a = 117.06 (3)°, β = 90.76 (2)°, γ = 61.71 (2)°, and Z = 4. The octahedral carbonyl cluster contains 12 terminal and three edge-bridging carbonyl groups. [NMe3(CH2Ph)]2[HFeIr5(CO)15] crystallizes in the triclinic space group [formula omited], with a = 10.218 (3) Å, b = 10.989 (4) Å, c = 20.757 (5) Å, α = 101.07 (2)°, β = 97.61 (2)°, γ = 108.13 (2)°, and Z = 2. The octahedral metal framework of the hydrido carbonyl cluster is surrounded by 11 terminal and four edge-bridging carbonyl groups; the hydrogen atom was located from the X-ray data and it is terminally bonded to iridium with a Ir-H distance of 1.60 (9) Å. [NMe3-(CH2Ph)][FeIr5(CO)16] crystallizes in the triclinic space group [formula omited], with a = 9.727 (2) Å, b = 16.296 (2) Å, c = 22.056 (2) Å, α = 79.99 (2)°, β = 80.61 (2)°, γ = 83.83 (l)°, and Z = 4. The metal carbonyl cluster possess a metal cage based on an octahedral unit surrounded by 12 terminal and four face bridging carbonyl groups. The electrochemical study of the redox propensity of [FeIr5(CO)16]- and [FeIr5(CO)15]3- allowed us to elucidate the mechanistic aspects of their interconversion. © 1991, American Chemical Society. All rights reserved.