Isolation of a Tetranuclear Intermediate Complex in the Synthesis of Paddlewheel‐Type Dirhodium Tetraacetate

To investigate the detailed mechanism of formation of the paddlewheel‐type dirhodium tetraacetate [Rh 2 (O 2 CCH 3 ) 4 (L) 2 ] ([ 1 ‐(L) 2 ]; L = axial‐coordinated solvent ligand), we performed a step‐by‐step synthesis. The isolated red intermediate complex [Rh 4 (μ‐Cl) 4 (O 2 CCH 3 ) 4 (L) 4 ] ([ 2 ‐(L) 4 ]) was characterized by means of single‐crystal X‐ray diffraction, 1 H NMR spectroscopy, infrared spectroscopy, and elemental analysis. The crystal structure of [ 2 ‐(MeOH) 4 ], which was crystallized from MeOH solution, has a unique twisted‐box Rh 4 (μ‐Cl) 4 core coordinated by four μ‐carboxylato bridging ligands and four MeOH molecules as axially coordinated solvent molecules. The electronic structure and absorption properties of [ 2 ‐(MeOH) 4 ] in MeOH were also carefully investigated both experimentally and theoretically.