Synthesis, Characterization, Absorption Properties, and Electronic Structures of Paddlewheel-Type Dirhodium(II) Tetra-μ-( n -naphthoate) Complexes: An Experimental and Theoretical Study.

The reactions of [Rh₂(O₂CCH₃)₄(OH₂)₂] with n -naphthalenecarboxylic acids ( n = 1: 1-HNC, n = 2: 2-HNC) afford the dirhodium tetra-μ-( n -naphthoate) complexes [Rh₂(1-NC)₄] ( 1 ) and [Rh₂(2-NC)₄] ( 2 ), respectively. Single crystal X-ray diffraction analyses of [1(OCMe₂)₂] and [2(OCMe₂)₂], which were obtained by recrystallization from acetone (OCMe₂) solutions of 1 and 2 , reveal that the dirhodium cores are coordinated by four equatorially bridging naphthoate ligands and two axial OCMe₂ ligands. Density functional theory (DFT) calculation confirmed that (i) the single Rh⁻Rh bond is formed between the two Rh ions and (ii) the electronic structures between two Rh ions in [1(OCMe₂)₂] and [2(OCMe₂)₂] are best described as π⁴δ²σ²δ*²π*⁴ and δ²π⁴σ²δ*²π*⁴, respectively. Time-dependent DFT (TDDFT) calculations clarify the absorption band characters of [1(OCMe₂)₂] and [2(OCMe₂)₂] ; the former shows the bands due to d⁻d and metal⁻to⁻metal-ligand charge transfer (MMLCT) excitations in the visible light region, whereas the latter shows the bands due to only d⁻d excitations in the same region. The electrochemical properties and thermal stabilities of [1(OCMe₂)₂] and [2(OCMe₂)₂] were also investigated in this study.