A new heterodinuclear mixed valence complex [(FeNiII)-Ni-III(BPBPMP)(OAc)(2)]ClO4 1 with the unsymmetrical N5O2 donor ligand 2-bis[{(2-pyridylmethyl)-aminomethyl}-6-{(2-hydroxybenzyl)(2-pyridylmethyl)}-aminomethyl]-4-methylphenol (H2BPBPMP) has been synthesized and characterized. 1 crystallizes in the monoclinic system, space group P2(1)/n, a = 12.497(2), b = 18.194(4), c = 16.929(3) Angstrom, beta = 94.11(3)degrees, V = 3839.3(12) Angstrom(3) and has an Fe-III Ni-II(mu-phenoxo)-bis(mu-carboxylato) core. Solution studies of 1 indicate that a pH-induced change in the bridging acetate occurs and the formation of an active [(OH)Fe-III(mu-OH)Ni-II(OH2)](+) species as the catalyst for phosphate diester hydrolysis and DNA interaction is proposed. In addition, the results presented here suggest that Ni-II would be a good candidate as a substitute of W in purple acid phosphatases. (C) 2003 Elsevier B.V. All rights reserved.