Research On Modification And Properties Of Polyoxometalates

Polyoxometalates(POMs), as an important family of metal-oxide clusters, have beenwidely studied for a long time. Recently, The design and construction of multifunctionalPOMs is currently of great interest not only because of their structural varieties but alsotheir potential applications in catalysis, medicine, magnetism, electrical conductivity andenergy storage. In this paper, eighteen new POMs, which are based on polyoxoanions andmetal cations or organic ligands, have been synthesized under hydrothermal conditions orby solvent diffusion method and characterized by elemental analyses, IR and X-ray singlecrystal diffraction. The magnetic and electrochemical properties of some compounds havealso been studied. The main results are as follows:1. Eleven new compounds based on polyoxomolybdate have been hydrothermallysynthesized by introducing metal cations or organic ligands:(H2pdn)(Hpdn){Mn(H2O)[Mn0.5Mo6O12(HPO4)3(PO4)(OH)3]}·2H2O(1)(Hdeta)(deta)[Mn0.5Mo6O12(H2PO4)3(HPO4)(OH)3]·4H2O(2)[H3O]3{Fe(H2O)[Fe0.5Mo6O12(HPO4)2(PO4)2(OH)3]}(3)(H2en)(Hen){Co(H2O)[Co0.5Mo6O12(HPO4)3(PO4)(OH)3]}·2H2O(4)(H2en)(Hen){Ni(H2O)[Ni0.5Mo6O12(HPO4)3(PO4)(OH)3]}·3H2O(5)(Hen)6{Cu(H2O)[CuMo12O24(H2PO4)3(HPO4)4(PO4)(OH)6]}·4H2O(6)(Hen)2(en)5[CdMo12O24(H2PO4)6(HPO4)2(OH)6]}·6H2O(7)(Hen)4(en)2{Cd(H2O)[CdMo12O24(H2PO4)3(HPO4)4(PO4)(OH)6]}·3H2O(8)(H2en)(Hen){Cd(H2O)[Cd0.5Mo6O12(HPO4)3(PO4)(OH)3]}·3H2O(9)(H2en)3[Mn3P4Mo4O28](10)(H2L)(HL)[PMo12O40](11)Compounds1-9are all based on [P4Mo6O31] unit. Both compounds2and7possess azero-dimensional unit formed by [P4Mo6O31]12-clusters and M2+cations. Compounds6and8represent a two-dimensional layered structure constructed from two kinds of[M(P4Mo6O31)2] clusters and [M(H2O)] coordination moieties, one [M(P4Mo6O31)2] clustercoordinates with four [M(H2O)] coordination moieties, the other coordinates with two [M(H2O)] coordination moieties. The others represent three-dimensional frameworks,constructed by [M(P4Mo6O31)2] clusters linking with [M(H2O)] coordination moieties, eachbasic [M(P4Mo6O31)2] unit coordinates with eight [M(H2O)] coordination moieties.Compound10exhibits unique three-dimensional adamantoid frameworks, interpenetratedby the right and left-handed Mo-O helical chains. The number of the two handed chains isidentical, so, compound10is mesomer. Compound11is a three-dimensionalsupermolecular framework, formed by hydrogen bonding between Keggin anions andorganic ligands. Magnetic susceptibility measurements indicate antiferromagneticinteractions within Mn2+ions in1, within Co2+ions in4and within Mn2+ions in10. Theelectrochemical results indicate that compounds3,6and10are potential electrocatalystsand modified electrode materials.By comparing the synthesis conditions and structures of compounds1-11, it can beconcluded that the pH of the reaction and the amount of organic amines play veryimportant roles in the assembly of polyoxometalate-based compounds. When the pH valuewas adjusted with inorganic base or a small amount of organic amines was added,molybdenum still presents+6oxidation state. When large amounts of reducing organicamines was added, MoVIis reduced to MoVduring the formation of [P4Mo6O31] clusters.The pH value determines the electron density of polyoxometalate, which affect thecoordination ability of polyoxometalates and result in different structures. And the organicligands with–CN groups also affect the structures of the products. If the volume of organicamines is larger, we just obtain a zero-dimensional unit formed by [P4Mo6O31]12-clustersand M2+cations. Thus it can be seen that organic amines not only act as organic base toadjust the pH value, but also act as the reductant and template.2. Four new compounds based on Keggin polyoxotungstate anions have beenhydrothermally synthesized:[Ni(pdn)3]2[PW12O40](OH)·H2O(12)(H2bipy)4(Hbipy)2[NiPW11O39]2(13)(Hbipy)3[PW12O40]·4H2O(14)(Cu2L)2[PW12O40](OH)·H2O (15) (H2L’)(HL’)[PW12O40]·2H2O(16)Compounds12,14and16exhibit three-dimensional supermolecular frameworksbased on [PW12O40]3-aions, which are generated by hydrogen bonding interaction. Whilecompound13shows a one-dimensional chains structure based on monovacant Keggin-typepolyoxotungstates anion [PW11O39]7-. Compounds15exhibits a three-dimensionalframework consisting of two-dimensional copper-L layers and polyoxoanions [PW12O40]3-.Magnetic susceptibility measurements indicate antiferromagnetic interactions within Ni2+ions in12and within Ni2+ions in13. And compound16shows excellent electrochemicalactivity.By comparing the synthesis conditions and structures of compounds12-14, it can beconcluded that both the pH of the reaction and the amount of organic amines are importantfactors for the synthesis of compounds12-14.3. Two new compounds based on vanadate have been synthesized:(H2en)(H1.5en)[H5V4.5P4O23]·H2O(17)(Et4N)4(H3O)4[HPV14O42](18)Compound17is a three-dimensional framework constructed by V-O-P clusters, it isinteresting that large cavities exit in compound17. And vanadium presents two kinds ofoxidation states. While compound18shows a zero-dimensional unit based on [PV14O42]9-anions, H3O+and Et4N+cations. Magnetic analysis indicates an antiferromagneticinteractions in compound17. And compound17also shows good electrochemical activity.pdn=1,2-diaminopropaneen=ethylenediaminedeta=diethylenetriamineL=1,4-Bis(triazol)butanebipy=4,4’-bipyridineL’=5,7,12,14-tetrahydro-quinoxalino[2,3-b]phenazineEt=ethyl...