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

Reactions of dinuclear rhodium(II) tetracarboxylates, [Rh-2(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, Na-2[Rh-2(O2CMe)(4)(NCO)(2)]center dot 4H(2)O (1), water and isocyanate, Na[Rh-2(O2CMe)(4)(NCO)(H2O)] (2), iodide, {K-2[Rh-2(O2CEt)(4)I-2]center dot H2O}(n) (3), and bromide ligands, {K-2[Rh-2(O2CEt)(4)Br-2]center dot H2O} (4) and K[Rh-2(O2CEt)(4)(Br)(0.5)](2)[Rh-2(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 S. Speciation of the [Rh-2(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.