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Syntheses, Structures And Property Studies Of Octamolybdate-based Inorganic-organic Hybrid Materials

Posted on:2011-08-15Degree:MasterType:Thesis
Country:ChinaCandidate:H Y ZangFull Text:PDF
GTID:2121360305989136Subject:Physical chemistry
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Polyoxometalate (POM) clusters have an unparalleled range of physical and chemical properties, acting as a set of versatile inorganic building blocks that can be reliably utilized in the formation of new materials. Our work is focused on the design and preparation of octamolybdate-based inorganic-organic hybrid materials. We have employed"one-pot"synthetic method and step-wise"bottom-up"synthetic strategy to synthesize twenty compounds with potential applications in semiconducting and photoluminescent materials. Furthermore, the compounds were characterized by elemental analysis, FT-IR, TGA, UV-vis spectra, fluorescence spectrometry.1. Under hydrothermal conditions, we employ the"one-pot"method to synthesize twelve transition-metal complex-modified octamolybdate hybrid materials by mixing (NH4)6Mo7O24·6H2O, organic ligands (L1 = 3-((1H-imidazol-1-yl)methyl)pyridine; L2 = 3-((1H-1,2,4-triazol-1-yl)methyl)pyridine; L3 = 2-(2-Pyridyl)imidazole and L4 = 2-(1-(Pyridine-3-ylmethyl)-1H-imidazol-2-yl)pyridine) and transition metals (Cu, Ni, Zn). CuII(HL1)2(H2O)2(Mo8O26) (1) CuII(L1)2(Mo8O26)0.5 (2) NiII(HL2)2(H2O)2(β-Mo8O26) (3) [CuII(HL2)2(Mo8O26)]·2H2O (4) [Cu2II(L2)4(Mo8O26)]·3H2O (5) Cu3I(L2)2(Mo8O26)0.5Cl (6) Cu4I(L2)4(Mo8O26) (7) Cu2II(L3)4(Mo8O26) (8) [Zn(HL4)2(H2O)(Mo8O26)]-2H2O (9) Cu2II(HL4)4(Mo8O26)2 (10) [CuIIL4(H2O)(Mo8O26)0.5]·2H2O (11) [CuIIL4(H2O)(Mo8O26)0.5]·2H2O (12) Single crystal X–ray diffraction results reveal that all the polyanions exhibitβisomer except thatθorγisomers in 2 and 12 respectively. The octamolybdate anions are modified by transition-metal complexes. The UV-vis reflectance spectra reveal that the compounds containing CuI ions not only have lower optical band gaps but also photoluminescent property. More interestingly,compound 6 is photoconductive. 2. Three novel compounds coexisting different isomers or forms of polymolybdate have been successfully synthesized. {[Ni(Mo8O26)(H2L1)2(H2O)](Mo8O26)(H2L1)}·2H2O (13) {[Co(Mo8O26)(H2L1)2(H2O)](Mo8O26)[Co(H2O)6]}·6H2O (14) [CuI6L24(Mo8O26)(Mo6O19)] (15) Crystal structure analysis reveals that 13 is a 1D+1D supramolecular structure coexisting bothγ-[Mo8O26N2] andγ-[Mo8O28] units; 14 hasγ-[Mo8O26]4- as well asβ-[Mo8O26]4- anions and 15 is a (3,4,6)-connected 2D network containing bothβ-[Mo8O26]4- and [Mo6O19]2- anions. According to quantum chemical calculations,the transformation fromβ-[Mo8O26]4- to [Mo6O19]2- is spontaneous in aqueous solution. Compound 15 shows a relatively lower optical band gap 1.69 eV.3. We have successfully explored the"bottom-up"strategy to step-wisely synthesize five compounds with octamolybdate anion exhibitingγisomer. [(H2L1)2(Mo8O26)]·4H2O (16) [Cu2I(L1)3(Mo8O26)0.5] (17) [(H2BIMB)(BIMB)0.5(Mo8O26)0.5]·H2O (18) [Ni(BIMB)2(HBIMB)2(Mo8O26)]·4H2O (19) [Zn(BIMB)2(Mo8O26)0.5] (20) Among them,compounds 16 and 18 are the designed synthons which act as precursors for the formation of compounds 17,19,20 which were obtained by post-modifying the synthons with metal ions. The optical band gap property for the five compounds and the photoluminescence of 20 were also investigeted.
Keywords/Search Tags:Polyoxometalates, Octamolybdate, Hybrid material, Semiconductor, Photoluminescence
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