Synthesis, structures, phase transformations and luminescence properties of solid uranyl phosphonates /
Three structurally different types of uranyl phosphonates
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1997.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://search.proquest.com/docview/304423145?accountid=7082 |
| Summary: | Three structurally different types of uranyl phosphonates were prepared in this research. The []-uranyl phenylphosphonate, []-UPP, and []-uranyl phenylphosphonate, []- UPP form infinite linear chains in which the uranyl ions are bridged by pairs of phenylphosphonate anions. The []-UPP arranges its phenyl groups in two rows standing perpendicularly to the chain in a cis-fashion, whereas []-UPP does so in the trans-fashion. At room temperature, []-UPP does not luminesce, whereas []-UPP luminesces strongly. The []-uranyl phenylphosphonate, []-UPP, and []-uranyl phenylphosphonate, []-UPP form infinite tubes in which the uranyl ions lie perpendicularly to the tube walls, and they are connected by the phenylphosphonate anions. In both compounds, the phenyl rings are on the outside of the tubes, and the neighboring tubes are not connected. At room temperature, []-UPP does not luminesce, whereas []-UPP does. Uranyl chloromethylphosphonate, UPMeCl, and uranyl methylphosphonate, UPMe form layered structures where the uranyl ions within the layers are bridged and chelated by the phosphonate anions, and the organic parts of the phosphonate anions protrude into the interlayer space. UPMeCl does not luminesce, but UPME does. At room temperature, single crystals of []-UPP undergo a solid-state transformation into []-UPP. The mechanism consists of breaking a U-Oequatorial bond followed by a rotation of a phenylphosphonate group, and a subsequent rearrangement of linear chains. Gaseous water molecules transfer protons from one phosphonate oxygen to another, which represents the rate-determining step of the transformation. In the presence of alkali ions in acidic aqueous environment, the linear-chain []-UPP and []-UPP transform into the tubular []-UPP. Isotope labeling experiments suggest that both compounds disassemble into individual uranyl and phenylphosphonate ions and reassemble in form of []-UPP. The differences between the luminescence properties of uranyl phenylphosphonates is attributed to different types of excitation energy migration. Resonant energy migration takes place in the luminescent []-UPP and []- UPP, whereas phonon-assisted energy migration predominates in the non-luminescent []-UPP and []-UPP. UPMeCl does not luminesce due to its chlorine atom which quenches the uranyl luminescence via electron transfer, whereas UPMe luminesces because it has no such quencher. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | x, 135 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 113-119. |