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

摘要

Two robust metal–organic frameworks (MOFs), {H_(4)[Ni(π-H_(2)O)_(2)]_(2)[Ni(rt-H_(2)O)_(2)]_(8)Ni_(4)(Tri)_(24)}[V~(IV)W_(12)O_(40)]_(2)·24H_(2)O ( 1 ) and {H[Ni(π-O)_(2)]_(2)[Ni(rt-H_(2)O)_(2)]_(8)Ni_(4)(Tri)_(24)}[V~(IV)W_(10)V~(V)_(2)O_(40)V_(2)][V~(IV)W_(9)V~(V)_(3)O_(40)V~(IV)_(2)]·24H_(2)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_(3)(Tri)_(6)(H_(2)O)_(4)}_(4)] ( {Ni _( 12 ) } ) in these two compounds. In 1 , the {Ni _( 12 ) } crown embraces four pendant Tri ligands that could capture a cationic [Ni(H_(2)O)_(2)]~(2+) group, resulting in the Ni_(13)-Tri building unit [Ni(H_(2)O)_(2){Ni_(3)(Tri)_(6)(H_(2)O)_(4)}_(4)] ( {Ni _( 13 ) } ). The {Ni _( 13 ) } building unit was fused together by Tri bridges into the 2D metal–organic layers, which are pillared by a typical Keggin-type POM [VW_(12)O_(40)]~(4–) 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_(2)O_(2) and oxidation of nitrite in neutral aqueous solution.