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.双核铑(II)四羧酸盐（dinuclear rhodium(II) tetracarboxylates）[Rh₂(O₂CR)₄]（R = 甲基(Me)、乙基(Et)）与卤化物（Br⁻、I⁻）或拟卤化物（OCN⁻）发生反应，可生成基于离子相互作用、具有独特超分子架构的双核配合物。本文所报道的配合物的固态排布结构，已通过单晶X射线衍射（single-crystal X-ray diffraction）完成表征。现已发现四类以异氰酸根、水与异氰酸根、碘离子、溴离子作为轴向配体的离散阴离子单元，对应配合物分别为：1. Na₂[Rh₂(O₂CMe)₄(NCO)₂]·4H₂O（标记为1）；2. Na[Rh₂(O₂CMe)₄(NCO)(H₂O)]（标记为2）；3. {K₂[Rh₂(O₂CEt)₄I₂]·H₂O}ₙ（标记为3）；4. {K₂[Rh₂(O₂CEt)₄Br₂]·H₂O}ₙ（标记为4）；5. K[Rh₂(O₂CEt)₄(Br)₀.₅]₂[Rh₂(O₂CEt)₄(H₂O)₂]（标记为5）。配合物1呈现出通过离子相互作用稳定的一维聚合物链结构，而配合物2至4均形成二维层状结构。配合物5则构建出包含两种双核铑结构单元的三维网状骨架。本研究通过紫外-可见滴定（UV–visible titrations）法对水溶液中[Rh₂(O₂CR)₄]/X⁻（R = Me、Et；X = OCN、Br、I）体系的物种分布进行了探究，以此阐释晶体态中不同Rh-X化学计量比产物的形成机制。最后，借助循环伏安法（cyclic voltammetry），评估了X⁻配位对这类双核铑(II)结构单元氧化性能的影响。