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This manuscript describes the syntheses, structures and magnetism of MnIII–CaII/SrII complexes which are compositionally relevant in the context of the oxygen evolving complex (OEC) of photosystem II (PS II). A series of trimetallic tetraoxo complexes containing redox-inactive metal ions CaII or SrII were synthesized using a tetranucleating ligand framework. The structural characteristics of these complexes, with the oxido ligands bridging the redox-inactive metals and the manganese centres, make them particularly relevant to biological and heterogeneous metal-oxido clusters. Electrochemical studies of these compounds show that the reduction potentials are highly dependent upon the Lewis acidity of the redox-inactive metal, identifying the chemical basis for the observed differences in electrochemistry. This correlation provides insights into the role of the CaII/SrII ion in modulating the redox potential of the OEC and of other redox-inactive ions in tuning the redox potentials of other metal-oxide electrocatalysts. Temperature dependent magnetic measurements have also been performed for the complexes. [ABSTRACT FROM AUTHOR]

The aim of the paper was to synthesize Mn/Ca entities that are structurally similar to the reported oxygen‐evolving complex (OEC) of photosystem II (PSII). Here we have ventured Schiff base combinations of racemic (±)‐3‐Aminopropane‐1,2‐diol and Salicyladehyde (H3L1)/o‐Vanillin (H3L2) with varied ratios of ligand : CaIIsalt : MnIIIsalt. Interestingly, H3L2 : CaCl2 : MnCl2 (2 : 1 : 1) afforded [{MnIII2CaII2(HL2)2Cl2(μ3‐OH)2(H2O)6}Cl2 ⋅ 2H2O] (3) whereas H3L1 : CaCl2 : Mn(acetate)2 (2 : 1 : 1) and H3L1 : CaCl2 : MnCl2 (2 : 1 : 2), generated [{MnIV(HL1)2}2 ⋅ 6H2O](1) and [{MnIII3MnII(HL1)3(μ2‐Cl)3(μ3‐O)} ⋅ 2CH3OH ⋅ 2H2O] (2) respectively. More importantly, we have been able to get a structure which offers partial similarity to reported structure of the OEC. Variable temperature magnetic susceptibility measurements have been performed in the 1.8–30 K region for all the compounds. Overall, these studies provide a critical understanding for the rational design and construction of synthetic OEC. [ABSTRACT FROM AUTHOR]