The mechanism of H 2 O 2 dismutation catalyzed by the recently reported 2,6-bis[((2pyridylmethyl)thio)methyl]pyridine-Mn(II) complex ([MnS 2 Py 3 (OTf) 2 ]) has been investigated by density functional theory using the S12g functional. The complex has been analyzed in terms of its coordination properties and the reaction of [MnS 2 Py 3 ] 2+ in a distorted square pyramidal coordination geometry with two hydrogen peroxide molecules has been investigated in our calculations. The sextet, quartet and doublet potential energy profiles of the catalytic reaction have been explored. In the first dismutation process the rate-determining step (RDS) is found to be the asymmetric O-O bond cleavage, which occurs on the sextet potential energy profile. A subsequent spin crossover from sextet to quartet can take place generating a stable Mn(IV) dihydroxo intermediate. This could disfavor the ping-pong mechanism commonly considered to describe the