Synthesis and structure of trinuclear clusters (Et4N)2[(μ3-Se)]Fe3(CO)9, [(μ-H)2Fe3(μ3-Se)(CO)9], and [(μ3-Se)FeMo2(η5-C5H5)2(CO)7]

The cluster anion Fe₃(μ₃-Se)(CO)₉]^2- (I) was isolated as a salt (Et₄N)₂I] by the reaction of Fe(CO)₅ with Na₂Se in isopropanol. The protonated form, (μ-H)₂Fe₃(μ₃-Se)(CO)₉ (II), was obtained by acidifying the reaction mixture and used for the synthesis of the heterometallic cluster FeMo₂(μ₃-Se)(CO)₇Cp₂ (III), CP=η⁵-C₅H₅. The structure of I and III was established by X-ray diffraction analysis. Crystals I are monoclinic, a=14.210(3), b=11.547(3), c=19.831(2), Å, β=90.92(2)°, V_cell=3254(1) ų, space group P2/c, Z=4, d_calc=1.550 g/cm³, Syntex P2₁, λCuK_α, R(F)=0.1333 for 1264 F_hkl>6σ(F_hkl). Crystals III are monoclinic, a=20.440(5), b=12.771(3), c=16.342(4) Å, β=113.80(2)°, V_cell=3903(2) ų, space group P2₁/c, Z=8, d_calc=2.222 g/cm³, Syntex P2₁, λCuK_α, R(F)=0.0734 for 1116 F_hkl>4σ(F_hkl). The structure of II was inferred from the Mössbauer, IR, and¹H and⁷⁷Se NMR spectroscopy data.