Multinuclear Transition Metal Sandwich-Type Polytungstate Derivatives for Enhanced Electrochemical Energy Storage and Bifunctional Electrocatalysis Performances.

Different transition metal (TM) units are introduced into a trivacant Keggin cluster to form three sandwich polytungstate derivatives, (Hen)[{K(HO)}{K(HO)}{Ni(HO)(en)}{Ni(HO)(PWO)}] (), [Cu(Himi){AsWO}]·5HO (), and (Hbtp)[FeFe(HO)(AsW O)]·4HO () (en = ethanediamine; imi = imidazole; btp = 1,3-bis(1, 2, 4-triazol-1-yl) propane). Compound is a 2,3,8-connected 3D network with {4}{4·6·8·6·8}{6} topology based on bisupported tetra-Ni sandwich phosphotungstate and two kinds of potassium connection units. Compound is a dense 12-connected 3D supramolecular network with {3·4·5} topology based on hexa-Cu(imi) sandwiched arsenotungstate. Compound represents the first mixed valence tetra-Fe substituted sandwich arsenotungstate assembly. Compounds - show enhanced supercapacitor performance (618.2, 603.4, and 504.6 F·g at a current density of 2.4 A·g 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 and exhibit dual-functional electrocatalytic behaviors in the reduction of iodate and the oxidation of dopamine for introduction of {Ni} and {Fe} units.