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.