The new heterodinuclear complex [(FeZnII)-Zn-III(BPBPMP)(OAc)(2)]ClO4 (1) with the unsymmetrical N5O2 donor ligand 2-bis[{(2-pyridylmethyl)-aminomethyl}-6-{(2-hydroxybenzyl)(2-pyridylmethyl)}-amino- methyl]-4-methylphenol (H2BPBPMP) has been synthesized and characterized by X-ray crystallography, which reveals that the complex cation has an (FeZnII)-Zn-III(mu-phenoxo)-bis(mu-carboxylato) core. Solution studies of 1 indicate that a pH-induced change of the bridging acetate occurs, and the formation of an active [(OH)(FeZnII)-Zn-III(OH2)] species as a highly efficient catalyst under weakly acidic conditions for phosphate diesters hydrolysis is proposed.