Discrete RhIII/FeIIand RhIII/FeII/CoIIICyanide-Bridged Mixed Valence Compounds

The heterotrinuclear complexes trans- and cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) are unprecedented examples of mixed valence complexes based on ferrocyanide bearing three different metal centers. These complexes have been assembled in a stepwise manner from their {trans-III-L(14S)Co(III)}, {cis-VI-L(15)Rh(III)}, and {Fe(II)(CN)(6)} building blocks. The preparative procedure follows that found for other known discrete assemblies of mixed valence dinuclear Cr(III)/Fe(II) and polynuclear Co(III)/Fe(II) complexes of the same family. A simple slow substitution process of [Fe(II)(CN)(6)](4-) on inert cis-VI-[Rh(III)L(15)(OH)](2+) leads to the preparation of the new dinuclear mixed valence complex [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) with a redox reactivity that parallels that found for dinuclear complexes from the same family. The combination of this dinuclear precursor with mononuclear trans-III-[Co(III)L(14S)Cl](2+) enables a redox-assisted substitution on the transient {L(14S)Co(II)} unit to form [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+). The structure of the final cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) complex has been established via X-ray diffraction and fully agrees with its solution spectroscopy and electrochemistry data. The new species [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) and [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) show the expected electronic spectra and electrochemical features typical of Class II mixed valence complexes. Interestingly, in the trinuclear complex, these features appear to be a simple addition of those for the Rh(III)/Fe(II) and Co(III)/Fe(II) moieties, despite the vast differences existent in the electronic spectra and electrochemical properties of the two isolated units.