| Polyoxoniobate is an important class of polyoxometalate.Compared with its polyoxometalate cousins,polyvanadate,polytungstate,and polymolybdate,polyoxoniobate has much higher charge,and has potential applications in nuclear waste disposal,alkaline catalytic and photochemical splitting of water.However,owing to the peculiar solution behavior,the development of polyoxoniobate is still at its early stage since1953.This thesis mainly concerns on the construction of new-type polyoxoniobates.Two types of compounds were obtained by utilizing different strategies,namely,isopolyniobate and heteropolyniobate.On one hand,five isopolyniobates were successfully synthesized by self-assembly of the precursor K7HNb6O1913H2O via the conventional aqueous solution method realizing structural transformation from{Nb6O19}to new-type cluaters.Further,the introduction of functional groups endows them potential applications in various fields.On the other hand,seven heteropolyniobates were synthesized by hydrothermal method.Central to the assembly and function of these heteropolyniobates is the heteroatom species,which templates their formation.The structures of them are determined by X-ray single crystal diffraction and further are confirmed by IR,element analysis,TGA results and UV-vis.Besides,the solution behaviors and magnetic property of some compounds are studied.The details are as follows:Isopolyniobate and derivatives:1)Four novel organic-inorganic hybrids based on{Nb16},{Nb19},{Nb20}and{Nb27},respectively,were obtained,namely,K3[H{Cu(2,2?-bipy)}4{Cu(2,2?-bipy)(H2O)}2(Nb16O48)]27H2O(1),[{Cu(2,2?-bipy)}4{Cu(2,2?-bipy)(H2O)}7(Nb19O58)](OH)6H2O(2),[{Cu(2,2?-bipy)}2{Cu(2,2?-bipy)(H2O)}9(Nb20O61)]35H2O(3,2,2?-bipy=C10H8N2),K11[Cu(en)2(H2O)2]2[H33{Cu(en)2}4{Cu0.5(en)2}4{Cu(en)2(H2O)}4(Nb27O76)4]82H2O(4,en=C2N2H8).The three Nb-oxo clusters{Nb16},{Nb19}and{Nb20}in compounds 1-3 are observed for the first time.The{Nb16}cluster of compound 1 can be seen as two{Nb6O19}units linked by a{Nb4O16}fragment,while{Nb19}of compound 2 and{Nb20}of compound 3 consists of two unique{Nb6O20}units linked by one{Nb7O28}and one{Nb8O32}fragment,respectively.In addition,the neighboring{Nb16}are combined together via[Cu(2,2?-bipy)]2+complexes forming a 1D chain.Interestingly,the Nb atoms of{Nb6O20}unit display six-coordinate and seven-coordinate environments.In addition,a new organic-inorganic tetramer besed on{Nb27}has been obtained,in which each{Nb27}cluster is decorated by Cu-complexes and four{Nb27}clusters are linked by[Cu(en)2]2+.Further,the neighboring polyoxoanions of compound 4 are combined together via[Cu(en)2]2+complexes forming a 1D chain.In addition,ESI-MS studies of compounds 1 and 4 confirm that{Nb16}and{Nb27}retain its integrity in water.2)A novel high-nuclearity Ni30-cluster embedded decamer based on{Nb6O19},K40Na3[H(Nb6O19)10{Ni30(H2O)8(OH)24}]70H2O(5),was synthesized.Compound 5 contains a{Ni30}encapsulated by ten Lindqvist-type{Nb6O19}building blocks.As we known,the cluster{Ni30}is the largest high-nuclear nickel-cluster in polyoxometalate family.Meanwhile,the decamer is the highest degree of polymerization of any polyoxoniobate based on{Nb6O19}.The solid-state magnetic susceptibility indicats the presence of antiferromagnetic exchange interactions and ESI-MS spectrum shows three envelopes corresponding to the intact cluster.Heteropolyniobate and derivatives:3)Three novel organic-inorganic hybrids based on trivacant Keggin subunit{Te Nb9},K6[H{Cu(phen)}12(H2O)2(Te5Nb15.5Cu0.5O57)2]·48H2O(6,phen=C12H8N2),{[{Cu(phen)}6(H2O)]2[Cu(en)2]3(HTe10Nb31Cu O114)}·52H2O(7),[Cu(H2O)2]1.5[Cu(en)2(H2O)]3[H8Si Te8Nb15O64]6H2O(8),have been successfully synthesized.Compounds 6 and 7 are directed by the tellurite anions,which act as heteroanion templates and linkers,as well as a pendant ligand.As far as we known,{Te5Nb15.5Cu0.5O57}possesses the largest number of heteroanion functioning as diverse roles in the polyoxoniobate family.Based on the Te-Nb system,compound 8 was isolated by introducing the second heteroatom species,which is directed by the Te IVand Si IVat the same time for the first time.The polyoxoanion can be seen as a sandwich-type structure,which consists of a novel{Si Te Nb6}subunit owing to Si IVion.Besides,the subunit{Si Te Nb6}is discovered for the first time in polyoxoniobate family.Unlike general sandwich-type polyoxometalates,the sandwiched sites are occupied by Te atoms.4)Two Cu-capped Keggin-type compounds,K[{Cu(2,2'-bipy)}6(H2PNb12O40)]20H2O(9)and K[{Cu(2,2'-bipy)}6(H2As Nb12O40)]20H2O(10),were obtained for the first time.Interestingly,the experiment has been performed for the successful isolation of a organic-inorganic hybrid isopolyoxoniobate based on{Nb10}by using 1,10-phen instead of 2,2'-bipy,which indicates that organic amine can act not simply as protective ligand but also as structure-directing agent.5)A new Cu-centred heteropolyoxoniobate,K20Na19[H18.5{Cu(en)2}2(H4Cu2Nb72O205)]277H2O(11),was synthesized successfully.In polyoxoanion,a novel{Nb20}cluster is formed containing two pentagonal{Nb(Nb)5}fragments,which is observed for the first time.ESI-MS studies confirm that the polyoxoanion retains its integrity in water for three days at least.6)Anew‘pure'inorganictransition-metal-bridgedheteropolyniobate,K6Na17[H3{Co(H2O)3}2(P4Nb9O40)2]24H2O(12),was synthesized,which contains two{P4Nb9}units decorated by two[Co(H2O)3]2+cations.Further,adjacent polyoxoanions are connected via[Co(H2O)3]2+complexes forming a 2D architecture. |
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