The introduction of hexavacant Dawson-type precursor K-12[H2P2W12O48]center dot 24H(2)O into a HOAc/NaOAc (OAc- = acetate) buffer system containing (NH4)(2)[Ce-IV(NO3)(6)] and Mn-II(OAc)(2)center dot 4H(2)O led to the isolation of a new compound, Na-20[Ce-3(IV)-(Mn2O6)-O-IV(OAc)(6)(H2O)(9)](2)[(Mn2P2W16O60)-P-III](3)c enter dot 21H(2)O (1). Compound 1 contains unusual triple-Dawson-type polyoxoanions [(Mn2P2W16O60)-P-III](3)(24-) and bipyramid-like 3d-4f heterometallic clusters [(Ce3Mn2O6)-Mn-IV-O-IV(OAc)(6)(H2O)(9)](2+), which are arranged in a 3-D supramolecular assembly with 1-D channels. The Na+ cations and solvent water molecules reside in the channels. Crystal data for 1 are as follows: hexagonal, P6(3)/mcm (No. 193), a=24.959(4) angstrom, c=26.923(5) angstrom, gamma=120 degrees, V=14525(4) angstrom(3), and Z=2. The electrochemical and electrocatalytic properties of compound 1 have been investigated.