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Capped Polyoxometalate Pillars between Metal–Organic Layers for Transferring a Supramolecular Structure into a Covalent 3D Framework

44

Citations

41

References

2018

Year

Abstract

Two robust metal-organic frameworks (MOFs), {H<sub>4</sub>[Ni(π-H<sub>2</sub>O)<sub>2</sub>]<sub>2</sub>[Ni(rt-H<sub>2</sub>O)<sub>2</sub>]<sub>8</sub>Ni<sub>4</sub>(Tri)<sub>24</sub>}[V<sup>IV</sup>W<sub>12</sub>O<sub>40</sub>]<sub>2</sub>·24H<sub>2</sub>O (1) and {H[Ni(π-O)<sub>2</sub>]<sub>2</sub>[Ni(rt-H<sub>2</sub>O)<sub>2</sub>]<sub>8</sub>Ni<sub>4</sub>(Tri)<sub>24</sub>}[V<sup>IV</sup>W<sub>10</sub>V<sup>V</sup><sub>2</sub>O<sub>40</sub>V<sub>2</sub>][V<sup>IV</sup>W<sub>9</sub>V<sup>V</sup><sub>3</sub>O<sub>40</sub>V<sup>IV</sup><sub>2</sub>]·24H<sub>2</sub>O (2) (Tri = 1,2,4-triazole), composed of polyoxometalates (POMs) and metal-organic units, were designed and synthesized by a hydrothermal method. Structure analysis indicates that there is a metal-organic crown [{Ni<sub>3</sub>(Tri)<sub>6</sub>(H<sub>2</sub>O)<sub>4</sub>}<sub>4</sub>] ({Ni<sub>12</sub>}) in these two compounds. In 1, the {Ni<sub>12</sub>} crown embraces four pendant Tri ligands that could capture a cationic [Ni(H<sub>2</sub>O)<sub>2</sub>]<sup>2+</sup> group, resulting in the Ni<sub>13</sub>-Tri building unit [Ni(H<sub>2</sub>O)<sub>2</sub>{Ni<sub>3</sub>(Tri)<sub>6</sub>(H<sub>2</sub>O)<sub>4</sub>}<sub>4</sub>] ({Ni<sub>13</sub>}). The {Ni<sub>13</sub>} building unit was fused together by Tri bridges into the 2D metal-organic layers, which are pillared by a typical Keggin-type POM [VW<sub>12</sub>O<sub>40</sub>]<sup>4-</sup> to construct a 3D supramolecular framework via the hydrogen bonds. Interestingly, the 2D metal-organic layer in 1 was successfully transferred into a 3D covalent MOF via extension of the length of the pillars by capping a Keggin-type POM with V-O units. Moreover, electrochemical behaviors and electrocatalytic properties of these two compounds were both studied, which can act as bifunctional electrocatalysts toward the reduction of H<sub>2</sub>O<sub>2</sub> and oxidation of nitrite in neutral aqueous solution.

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