Reaction of the dinuclear bis(mu-hydroxo) complex 2 with 3,5-diisopropylpyrazole yielded a dinuclear (mu-hydroxo)(mu-pyrazolato)dimanganese(II) complex 4, which reacted with H2O2 in the absence of excess pyrazole to give the mononuclear Mn(III) side-on peroxo complex containing a neutral pyrazole ligand. However, hydrolytic equilibrium of the bridging pyrazolate ligand of the (mu-hydroxo)(mu-pyrazolato)dimanganese(II) complex was observed in the presence of H2O.