Syntheses, Structures And Photocatalytic Properties Of The Self-assembly Polymers Based On Keggin Type W/Nb Mixed-addendum Polyoxometalate

Polyoxometaltes(POMs) wide structural diversity and its unique physical and chemical properties, making it a veritable nano molecular clusters, mainly used in materials science and energy transition to catalysis and medicine. Polyoxoniobates(PONbs), as a burgeoning subclass, have attracted increasing interest because of their intriguing features and multifarious applications in virology, nuclear waste treatment, the base-catalyzed decomposition of biocontaminants, and photocatalytic water splitting activity.In this paper, we chose the Keggin type Nb/W mixed-addendum polyoxometalate as fundamental building block, and successfully obtained a tetramer {Nb16O30} cluster and two sandwich-type compouds through self-assembly principle and the formation of Nb–O–Nb bridge under acidic conditions. The new compounds have been synthesized under hydrothermal synthesis or conventional synthesis, and characterized by single crystal X-ray diffractions, IR spectroscopy, thermogravimetric analysis, and solution electrochemistry. Moreover, the photocatalytic properties of them have been studied.1. Under hydrothermal synthesis condition, a tetrameric polyoxometalate(POM) has been synthesized based on Keggin type Nb/W mixed-addendum POM [Si W9(Nb O2)3O37]7– by controlling of the reaction conditions and adjusting solution acidity:Cs19K2[Nb4O6(Si W9Nb3O40)4]Cl·27H2O(1)Compound 1 was built from four {Si W9Nb3O40} structural units which are connected with an adamantane-like {Nb4O6} tetrahedral core to form a {Nb16O30} cluster. All the niobium atoms in the {Nb16O30} cluster of 1 adopt six-coordinated Nb O6 octahedral mode. The photocatalytic investigation indicates that the incorporation of Nb into the polysilicotungstate can effectively enhance the photocatalytic H2 evolution ability.2. Utilizing the nucleophilicity of Ot(Nb)(Ot: terminal oxygen), two novel Nb–O–Cr bridge-based POMs with sandwich-type structures were isolated by the reaction of saturated Nb/W mixed-addendum POM [Ge W9(Nb O2)3O37]7- and Cr3+ under different acidic conditions:Cs7[(Ge W9Nb3O39)2Cr(H2O)4]·10H2O(2)Cs4Na2[(Ge W9Nb3O39.5)2Cr2(H2O)8]·7H2O(3)2 and 3 all contain two isomorphic sandwich like {Ge Nb3W9O40} fragments which are held together via different molar ratios of Nb–O–Nb bridge and(Nb)Ot–Cr–Ot(Nb) bridge. All the CrШ atoms are selectively bonded to Ot(Nb) of {Ge W9Nb3O40} fragments, indicating the high nucleophilicity of Ot(Nb). Photodegradation of the Rh B system in the existence of 2 and 3 reveals that 2 and 3 may be potential photocatalysts for degradation of some organic dyes.