The trimanganese sandwich complex [NaMn3II (H2O)(2)(P2W15O56)(2)](17) (abbreviated {NaMn3P4W30}) has been characterized by FTIR spectroscopy, P-31 NMR spectroscopy and elemental analysis. Despite the close structural similarity of {NaMn3P4W30} with the parent anion alpha beta beta alpha-[Mn-4(H2O)(2)(P2W15O56)(2)](16-) (abbreviated {Mn4P4W30}), the two compounds exhibit slightly different electrochemical behaviors. By comparison with {Mn4P4W30}, the Mn-II centers of {NaMn3P4W30} are more difficult to oxidize while the W centers are more easily reduced. Both complexes present a catalytic effect on nitrite reduction. (C) 2007 Elsevier B.V. All rights reserved.