Synthesis and chemical characterization of the chalcogenide capped iridium carbonyl anions: [Ir3(µ3-X)2(CO)6]–(X = S or Se). Crystal and molecular structures of [NMe3(CH2Ph)][Ir3(µ3-S)2(CO)6] and [NMe4][Ir3(µ3-Se)2(CO)6]

Abstract

Reaction of [Ir₄(CO)₁₂] or [Ir₆(CO)₁₆] in tetrahydrofuran with SCN^–, SeCN^– or polysulphides in MeOH gives the trinuclear anions [Ir₃(µ₃-X)₂(CO)₆]^–(X = S or Se) which have been isolated and investigated by X-ray analysis. The salt [NMe₃(CH₂Ph)][Ir₃(µ₃-S)₂(CO)₆](1) crystallizes in the monoclinic space group P2₁/n(no. 14) with a= 9.303(2), b= 17.295(3), c= 28.274(4)Å, β= 94.19(2)°, Z= 8, R= 0.027 for 3 676 significant independent reflections having I > 3σ(I). The salt [NMe₄][Ir₃(µ₃-Se)₂(CO)₆](2) crystallizes in the monoclinic space group C2/c(no. 15) with a= 15.930(3), b= 7.877(2), c= 15.040(2)Å, β= 108.22(2)°, Z= 4, R= 0.025 for 1 045 significant independent reflections having I > 3σ(I). Both structures were solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares methods. The anions consist of an Ir₃ triangle bicapped by triply bridging chalcogenide atoms. Each iridium atom, bearing two terminal CO groups, displays an almost square-planar geometry with respect to the ligands. In both compounds the Ir–Ir distances are long [mean values 3.086(1) and 3.170(1)Å for compounds (1) and (2) respectively] and suggest a very weak (if any) metal–metal interaction. The two anions can be considered therefore as trinuclear Ir^I metal aggregates rather than triangular clusters.