Inorganic Chemistry, Vol.58, No.12, 7947-7957, 2019
A Host-Guest Supercapacitor Electrode Material Based on a Mixed Hexa-Transition Metal Sandwiched Arsenotungstate Chain and Three-Dimensional Supramolecular Metal-Organic Networks with One-Dimensional Cavities
The mixed hexa-transition metal (hexa-TM) sandwiched arsenotungstate derivative, [Cu-3(I)(pz)(2)(Phen)(3)](2)[Cu-I(phen)(2)][{Na(H2O)(2)}{((V5CuO6)-Cu-IV-O-II)((AsW9O33)-W-III)(2)}]center dot 6H(2)O (1) (pz = pyrazine; phen = 1,10-phenanthroline), has been hydrothermally synthesized and structurally characterized. In compound 1, two {AsW9O33} clusters are connected by mixed hexa-TM ring unit {(V5CuO6)-Cu-VI-O-II} to form a sandwich-type dimer, which are further bonded in "ABAB" mode by the {Na(H2O)(2)} linker resulting in pure inorganic chains. The unique "L-shaped" trinuclear complex {Cu-3(phen)(3)(pz)(2)} is supported together via staggered pi-pi interactions to generate extending waveform two-dimensional supramolecular layers, which are further aggregated with their adjacent analogues by complexes {Cu(phen)(2)} via H-bonding interaction to yield an unprecedented three-dimensional (3D) metal-organic networks with one-dimensional (1D) cavities. The pure inorganic 1D sandwich chains are implanted in the cavities as guest units via supramolecular interactions to form a POMOF 3D framework. Compound 1, as the electrode of the supercapacitor, exhibits higher specific capacitances (825 F g(-1) at a current density of 2.4 A g(-1)), better rate capability, more durable cyclic stability (91.4% of cycle efficiency after 3000 cycles), and improved conductivity and electroactivity compared to those of parent polyoxometalate (POM) Na-9[AsW9O33]center dot 19H(2)O(2) and 6-Cu-substituted POM [Cu-6(imi)(6) {(AsW9O30CI3)-W-III}(2)]center dot 6H(2)O (3), which may be attributed to the introduction of V4+, the unique host-guest structure, and the rich pi electron system. In addition, compound 1 exhibits dual-function electrocatalytic behavior in reducing inorganic salt IO3- and oxidizing the organic molecule dopamine.