Characterization and electrochemical properties for rhenium(III) ion incorporated into linear-type S-bridged trinuclear complexes. Crystal structures of ΔΛ- and ΔΔ/ΛΛ-[Re{Ir(aet)3}2]3+ (aet=2-aminoethanethiolate)

Abstract The meso ( 1a ) isomer of the Ir III Re III Ir III trinuclear complex [Re{Ir(aet) 3 } 2 ] 3+ (aet=2-aminoethanethiolate) was newly prepared by SnCl 2 ·2H 2 O reduction of an acidic mixture of fac ( S )-[Ir(aet) 3 ] and NH 4 ReO 4 , and purified by column chromatography. The racemic ( 1b ) isomer was isolated by the reaction of fac ( S )-[Ir(aet) 3 ] with [Re(Metu) 6 ]Cl 3 (Metu= N -methylthiourea). The crystal structures of 1a Br 3 and 1b Br 3 ·H 2 O were determined by X-ray crystallography. Both isomers consist of two terminal fac ( S )-[Ir(aet) 3 ] units and a central Re atom, forming the linear-type S-bridged trinuclear structure. The central Re atom is situated in an octahedral environment with Re III S 6 chromophore. Both 1a and 1b are fairly stable in water under aerobic condition and they were characterized spectrochemically. Further, 1b was optically resolved by a column chromatographic method, and it is characterized by CD spectroscopy. The Re III ion, which has a d 4 -electronic configuration, in 1b indicates a lower magnetic moment (1.11μ B ) at room temperature, reflecting well the paramagnetic shifts for 1 H and 13 C NMR signals. Each cyclic voltammogram of [Re{M(aet) 3 } 2 ] 3+ (M=Ir III , Rh III ) shows a reversible redox process (M IV/III ) in a positive region and they are confirmed by a spectroelectrochemical technique. Their redox potentials at E 0 ′=+0.34–+0.60 V (vs . Ag/AgCl) are lower than those for the corresponding complexes, whereas it was elucidated that the oxidation state of the Re III ion is highly stabilized in the S-bridged trinuclear structures.