| As well known, introduction of transition-metal (TM) clusters into polyoxometalates(POMs), or POM-based inorganic-organic hybrid materials could functionalize POMmatrices. In the past decades, the polyoxotungstates, polyoxomolybdates andpolyoxovanadates modified transition-metal by have made great progress, because they canbe easily obtained by simple acidification and are stable over a wide pH range. However, itis difficult to explore the TM-modified polyoxoniobates (PONs), as the difficulty for TMcations co-existence with the PON precursors under alkaline conditions, and the difficultyin activating surface oxygen atoms of PONs. However, the design and synthesis of the TM-modified PONs, especially heteropolyoxoniobates, have received more and more attentionrecently as their fascinating physical chemical properties and potential applications invirology, nuclear waste treatment and photocatalytic materials.In this paper, eight new TM-modified polyoxoniobates have been synthetized byhydrothermal method and conventional method, and the crystal structures alsocharacterized by single crystal X-ray diffractions, XPS, IR and TG-DTA. The antitumorproperty of compounds of1and2, photocatalytic hydrogen evolution activity ofcompounds of5and6, and photodegradative property of compound7have beeninvestigated.Reactions of hexaniobate with vanadate in the presence of Ni2+, Zn2+or Cu2+lead tothree high-nuclear vanadium cluster-substituted heteropolyoxoniobates (HPNs):{Ni(en)3}5H{VVNb8VIV8O44}·9H2O (1),(H2en)Na2[{Zn(en)2(Hen)}{Zn(en)2(H2O)}2{PNb8VIV8O44}]·11H2O (2) and Na{Cu(en)2}3{[Cu(en)2]2[PNb8VIV8O44]}·11H2O (3).Structural analysis reveals that compounds1-3contain the similar {V8}-substituted[XVNb8VIV8O44]11-(X=P, V) clusters, obtained by inserting {V8} ring into tetravacant HPN[XNb8O36]27-. To our knowledge, compounds1-3represent the first high-nuclear vanadiumcluster-substituted HPNs, and compound1is the biggest vanadoniobate cluster in the HPNchemistry. Interestingly, the nickel and zinc cations are firstly introduced into HPNs, whichmight promise a richer set of structures in the HPN family. Antitumor study indicates thatcompounds1and2both exhibit high activity against human gastric cancer SGC-7901cells,SC-1680cells and MG-63cells.Two3D HPN-based frameworks [Cu(en)2]4[PNb12O40(VO)6]·(OH)5·8H2O (5) and[Cu(enMe)2]4[PNb12O40(VO)6]·(OH)5·6H2O (6)(en=1,2-ethylenediamine, enMe=1,2-diaminopropane) were obtained by reaction of K7HNb6O19·13H2O, H3PO4and NaVO3with the assistance of Cu2+cation and en under hydrothermal conditions. To our knowledge, the compounds5and6both contain the first hexa-capped Keggin phosphoniobate:[PNb12O40(VO)6]3-, and the phosphoniobate was firstly used as the building blocks forconstructing the3D framework materials. Photocatalytic studies indicated that compounds5and6exhibit photocatalytic water reduction activity.Two organic–inorganic hybrid polyoxoniobatesNa4[Cu(en)2(H2O)2]5[Na6Ge8Nb32O108H8(OH)4]·41H2O (7) andNa3[Cu(en)2(H2O)2]1/2{[Cu(en)2]2Nb6O19}·8H2O (8) were synthesized by reaction of theinorganic GeO2and K7HNb6O19·13H2O with the assistant of Cu2+, Na+and en moleculesunder hydrothermal system and conventional aqueous condition, respectively. To ourknowledge, compound7was the first organic–inorganic hybrid germanoniobate cluster andthe largest germanoniobate observed in the literatures up to date. The {Ge4Nb16} anion isfurther connected by a {Na6} cluster into a pseudo-sandwich-type polyoxoanion, whichrepresents the first sandwich-type structure based on two germanoniobate units. Further, thesandwich-type polyoxoanions were connected by the counter groups [Na2Cu(en)2H2O]4+intoa3D supramolecular porous framework. Photocatalytic study reveals that compound7exhibits good photocatalytic activity for the degradation of MB. |
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