Substituent Effects on Core Structures and Heterogeneous Catalytic Activities of MnIII(μ-O)2MnIV Dimers with 2,2′:6′,2″-Terpyridine Derivative Ligands for Water Oxidation

[(OH2)(R-terpy)Mn(μ-O)2Mn(R-terpy)(OH2) ]3+ (R-terpy = 4′-substituted 2,2′:6′,2″-terpyridine, R = butoxy (BuO), propoxy (PrO), ethoxy (EtO), methoxy (MeO), methyl (Me), methylthio (MeS), chloro (Cl)) have been synthesized as a functional oxygen-evolving complex (OEC) model and characterized by UV–vis and IR spectroscopic, X-ray crystallographic, magnetometric, and electrochemical techniques. The UV–vis spectra of derivatives in water were hardly influenced by the 4′-substituent variation. X-ray crystallographic data showed that Mn centers in the MnIII(μ-O)2MnIV cores for derivatives with R = H, MeS, Me, EtO, and BuO are crystallographically indistinguishable, whereas the derivatives with R = MeO and PrO gave the significantly distinguishable Mn centers in the cores. The indistinguishable Mn centers could be caused by rapid electron exchange between the Mn centers to result in the delocalized Mn(μ-O)2Mn core. The exchange integral values (J = −196 to −178 cm–1) for delocalized cores were lower than that (J...