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

Abstract

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 C_3v 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 R, 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 D_3d symmetry.