Synthesis and crystal and molecular structures of mixed-valence tetranuclear, [Re4I8(CO)6], and trinuclear, [ Re3I6(CO)6], compounds of rhenium obtained by di-iodine oxidation of rhenium(I) carbonyl complexes

Di-iodine oxidation of [Re2I2(CO)6(thf)2] (thf = tetrahydrofuran) at room temperature in heptane as solvent gave [ReI3(CO)3] (1) and the tetranuclear [Re4I8(CO)6] (2). A mononuclear molecular structure of C3v symmetry is suggested for (1), on the basis of spectroscopic and magnetic susceptibilty measurements. The reaction of [Re2I2(CO)8] with di-iodine at the reflux temperature of heptane gave the trinuclear complex [Re3I6(CO)6] (3). The crystal and molecular structures of both (2) and (3) have been solved by X-ray diffraction methods. Compound (2) is monoclinic, space group C2/c, z = 4, with unit-cell dimensions a = 22.316(4), b = 8.679(3), c = 12.705(3) Å, β = 96.02(2)°; R = 0.059 for 1 700 observed reflections. It belongs to the family of [Re2X8]2- complexes, with bridging iodine to two terminal Re(CO)3 groupings. Compound (3) is trigonal, space group R3, Z = 3, with dimensions a = 6.915(2) and c = 36.939(3) Å; R = 0.068 for 490 observed reflections. It comprises a ReI6 central core iodide-bridged to two terminal Re(CO)3 groupings in a molecular geometry of idealized D3d symmetry