Different transition metal (TM) units are introduced into a trivacant Keggin cluster to form three sandwich polytungstate derivatives, (H(2)en)[{K(H2O)(0.5)}(2){K-2(H2O)(3)}{Ni(H-2)(en)(2)}(2){Ni-4(H2O)(2) (PW9O34)(2)}] (1), [Cu-6(Himi)(6)-{(AsW9O33)-W-III}(2)]center dot 5H(2)O (2), and (H(2)btp)(4)[(Fe2Fe2II)-Fe-III(H2O)(2)(AsW9O34)(2)]4H(2)O (3) (en = ethanediamine; imi = imidazole; btp 1,3-bis(1, 2, 4-triazol-1-yl) propane). Compound 1 is a 2,3,8-connected 3D network with {4(3)}(2){4(6).6(6).8(3). 6(12).8}{6}(2) topology based on bisupported tetra-Ni sandwich phosphotungstate and two kinds of potassium connection units. Compound 2 is a dense 12connected 3D supramolecular network with {3(24).4(36).5(6)} topology based on hexa-Cu(imi) sandwiched arsenotungstate. Compound 3 represents the first mixed valence tetra-Fe substituted sandwich arsenotungstate assembly. Compounds 1-3 show enhanced supercapacitor performance (618.2, 603.4, and 504.6 F.g(-1) at a current density of 2.4 A.g(-1) with 91.5%, 89.3%, and 87.8% of cycle efficiency after 5000 cycles, respectively) compared to their maternal polyoxometalates (POMs) and most reported POM-based electrode materials, which suggests that the introduction of multinuclear TM into vacant POMs is an effective method to improve the energy storage performance of POMs. In addition, compounds 1 and 3 exhibit dual-functional electrocatalytic behaviors in the reduction of iodate and the oxidation of dopamine for introduction of {Ni-4} and {Fe-4} units.