The trans-Mn ^III (Salophen)(OH₂)₂ ^{+ and bioxalate (HOX −) in aqueous medium equilibrate rapidly to trans-Mn III (Salophen)(OH₂)(HOX) followed by the acid dissociation equilibrium to the (aqua) mono oxalato complex. The slow redox reactions of trans-Mn III (Salophen)(OH₂)(HOX/OX)0/− with H₂OX, HOX −,OX2−obey second order kinetics satisfying 2:1 stoichiometry ([MnIII]_T/[OX]_T=2/1). The products are MnII and CO2. Acrylamide monomer has no effect on the rate constant and the reaction does not induce its polymerization.The rate and activation parameters for the various rate limiting paths are reported. The intramolecularreduction of MnIII by the coordinated HOX − and OX₂}

− in trans-Mn^III(Salophen)(OH₂)(HOX/OX)⁰/

− couldnot be detected. Contrary to our expectation, it is observed that H₂OX is a better reducing agent than HOX ⁻ for trans-Mn^III(Salophen)(OH₂)(HOX), the slowest being the redox reaction of OX²

− with trans-Mn^III(Salophen)(OH₂)(OX)⁻. The molecular modelling by DFT depicts the structural trans effect in the oxalatocomplexes, it being maximum for trans-Mn^III(Salophen)(OH₂)(OX)⁻. The observed sequence of the redoxactivity of the oxalato complexes reflects the potential role of non-covalent interaction i4e. H-bonding, governingthe proton controlled electron transfer process (PCET). The Mn^III(Salophen/Salen) complexes may turn out tobe good substitute candidates for Oxalo Oxidase (OXO) enzyme in alleviating the oxalate overload in plantsand animal biochemistry.