Main-Group-Organotransition-Metal Chemistry: The Cyclopentadienylchromium Polyiodides Including [(C₅Me₅)₂Cr₂I₃⁺]₂[I₁₆^2-]

The reaction of [Cp*Cr(CO)₂]₂ (Cp* = η⁵-C₅Me₅) and I₂ affords a compound of the empirical formula Cp*CrI₃ (2). Single-crystal X-ray diffraction shows 2 to be a polymer, {[Cp*CrI(μ-I)]₂·[Cp*Cr(I ₃)(μ-I)]₂}_n [monoclinic P2₁/c; a = 15.658 (2), b = 8.504 (1), c = 23.242 (4) Å; β = 102.48 (1)°; V = 3021.7 (9) ų; Z = 2; ρP_calc = 2.497 g cm^-3; 3014 observed reflections I > 2.58σ(I); R = 0.039, R_w = 0.041]. ¹H NMR studies show that in chlorinated solvents 2 dissociates into [Cp*CrI(μ-I)]₂ (1), the latter of which can be prepared by reduction of 2 with Zn/Hg. Treatment of 2 with high concentrations of I₂ (I/Cr of >6) gives Cp*CrI_5.5 (3), which is formulated as [Cp*₂Cr₂(μ-I)₃]₂[I ₁₆] [monoclinic, P2₁/c; a = 14.744 (2), b = 22.864 (4), c = 23.267 (5) Å; β = 93.77 (2)°; V = 7827 (4) ų, Z = 4; ρ_calc = 3.005 g cm^-3; 6153 observed reflections I > 2.58σ(I); R = 0.054, R_w = 0.063]. The cation exhibits a short Cr-Cr distance of 3.00 (1) Å indicative of Cr(III)-Cr(III) bonding. This cation is imbedded within a three-dimensional polyiodide lattice based upon I₁₆^2- subunits. The I₁₆^2- cluster is comprised of an I₂-linked pair of roughly planar (I₂)₃I^- subunits.