Search for Structurally Resembled Mn/Ca Cubane Core of the Oxygen Evolving Complex of Photosystem II Yielded Mn^IV, Mn^III₃Mn^II and Mn^III₂Ca^II₂Entities: Structure and Magnetism

Abstract

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.