Structural Diversity in Paddlewheel Dirhodium(II) Compounds through Ionic Interactions: Electronic and Redox Properties

Reactions of dinuclear rhodium­(II) tetracarboxylates, [Rh2­(O2CR)4] (R = Me, Et), with halides (Br– and I–) or pseudohalides (OCN–) yield dinuclear complexes with intriguing supramolecular architectures based on ionic interactions. The solid-state arrangement of the complexes presented here has been studied using single-crystal X-ray diffraction. Discrete anionic units with the axial positions occupied by isocyanate, Na2­[Rh2­(O2CMe)4­(NCO)2]·4H2O (1), water and isocyanate, Na­[Rh2­(O2CMe)4­(NCO)­(H2O)] (2), iodide, {K2­[Rh2­(O2CEt)4­I2]·H2O}n (3), and bromide ligands, {K2­[Rh2­(O2CEt)4­Br2]·H2O}n (4) and K­[Rh2­(O2CEt)4­(Br)0.5]2­[Rh2­(O2CEt)4­(H2O)2] (5), have been found. Complex 1 shows monodimensional polymeric chains stabilized through ionic interactions, while complexes 2–4 consist of two-dimensional layers. Finally, a three-dimensional network containing two kinds of dirhodium moieties has been found in complex 5. Speciation of the [Rh2­(O2CR)4]/X– (R = Me, Et; X = OCN, Br, I) systems was investigated in aqueous solution by UV–visible titrations, helping us to rationalize the obtention of different Rh–X stoichiometries in the crystal state. By cyclic voltammetry, we have evaluated the effect of X– coordination on the oxidation properties of these dirhodium­(II) units.