The First Triple Thiol-thiolate Hydrogen Bond versus Triple Diselenide Bond That Bridges Two Metal Centers

Treatment of fac(S)-[Rh(aet)3] (aet = 2-aminoethanethiolate) with aqueous HBF4 in air led to the protonation at coordinated thiolato groups to give a rhodium(III) dimer, [{Rh(aet)2(Haet)}{Rh(aet)(Haet)2}](BF4)3 ([1](BF4)3). On the other hand, similar treatment of fac(Se)-[Rh(aes)3] (aes = 2-aminoethaneselenolate) produced a dinuclear rhodium(III) complex, [Rh2(selenocystamine)3](BF4)6 ([2](BF4)6), because of the autoxidation of coordinated selenolato groups by air. The crystal structures of [1](BF4)3, ΔΔ-[1](BF4)3, and [2](BF4)6 were determined by X-ray crystallography. In [1]3+ two RhIII octahedrons are connected through a strong triple thiol-thiolate S−H···S hydrogen bond, while two RhIII octahedrons are directly joined by a triple diselenide bond in [2]6+. The cyclic voltammetry indicated that in acidic media the RhIII center in fac(Se)-[Rh(aes)3] is more easily oxidized to RhIV than that in fac(S)-[Rh(aet)3], which is responsible for the formation of coordinated diselenide bonds.