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 [Rh(2)(O(2)CCH(3))(4)(OH(2))(2)] with n-naphthalenecarboxylic acids (n = 1: 1-HNC, n = 2: 2-HNC) afford the dirhodium tetra-μ-(n-naphthoate) complexes [Rh(2)(1-NC)(4)] (1) and [Rh(2)(2-NC)(4)] (2), respectively. Single crystal X-ray diffraction analyses of [1(OCMe(2))(2)] and [2(OCMe(2))(2)], which were obtained by recrystallization from acetone (OCMe(2)) solutions of 1 and 2, reveal that the dirhodium cores are coordinated by four equatorially bridging naphthoate ligands and two axial OCMe(2) 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(OCMe(2))(2)] and [2(OCMe(2))(2)] are best described as π(4)δ(2)σ(2)δ*(2)π*(4) and δ(2)π(4)σ(2)δ*(2)π*(4), respectively. Time-dependent DFT (TDDFT) calculations clarify the absorption band characters of [1(OCMe(2))(2)] and [2(OCMe(2))(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(OCMe(2))(2)] and [2(OCMe(2))(2)] were also investigated in this study.