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Title: Synthesis and Characterization of Bimetallic Zintl Clusters and their Use in the Fabrication of Intermetallic Nanoparticles
Authors: Downing, Domonique Onike
Advisors: Eichhorn, Bryan W
Department/Program: Chemistry
Type: Dissertation
Sponsors: Digital Repository at the University of Maryland
University of Maryland (College Park, Md.)
Subjects: Chemistry
Inorganic chemistry
Materials Science
Keywords: intermetallic phase
nanoparticle fabrication
platinum group metal
sigma aromaticity
Zintl cluster
Issue Date: 2012
Abstract: In this thesis, the synthesis, characterization and applications of bimetallic Zintl clusters are explored. Zintl ions are polyanions of main group elements, primarily of the heavier elements of groups 14 and 15. The closo-Sn<sub>9</sub>Ir(cod)<super>3-</super>, Sn<sub>9</sub>Rh(cod)<super>3-</super>, and Pb<sub>9</sub>Ir(cod)<super>3-</super> ions were prepared from precursors E<sub>9</sub><super>4-</super> (E = Sn, Pb), [M(cod)Cl]<sub>2</sub> (M = Rh, Ir) and 2,2,2-crypt in ethylenediamine/toluene solvent mixtures. The clusters were isolated and characterized via NMR spectroscopy and single-crystal X-ray diffraction studies. The closo-E<sub>9</sub>Ir(cod)<super>3-</super> ions are the first known Ir(I) Zintl clusters and are examples of isostructural Sn/Pb homologues. All three complexes have 22-electron, bicapped square-antiprismatic structures and pseudo-C4v point symmetry with the Ir(cod) and Rh(cod) vertices attached in an &eta;<super>4</super> fashion. The Sn<sub>9</sub>Rh(cod)<super>3-</super> ion possesses <super>119</super>Sn NMR chemical shifts that are consistent with other known Sn<sub>9</sub><super>4-</super> transition metal derivatives. The structural studies and <super>1</super>H and <super>13</super>C NMR studies showed significant charge transfer to the cod ligands. Novel Rh@Sn<sub>12</sub><super>3-</super> and Rh@Pb<sub>12</sub><super>3-</super> ions have been prepared and isolated in the solid state and the latter has been studied via <super>207</super>Pb NMR. The ions are 26-electron clusters with near perfect icohsahedral Ih point symmetry. Additionally, Ir@Pb<sub>12</sub><super>3-</super> and the previously isolated Ir@Sn<sub>12</sub><super>3-</super> ion [Fässler <italic>et al.</italic> 2010, <italic>Chem. Eur. J.</italic>] were detected for the first time via <super>207</super>Pb and <super>117</super>Sn NMR, respectively. The <super>207</super>Pb NMR of Rh@Pb<sub>12</sub><super>3-</super> and Ir@Pb<sub>12</sub><super>3-</super> have the most downfield 207Pb signals known to date, due to their &sigma;-aromaticity. The Sn<sub>9</sub><super>4-</super> and As<sub>7</sub><super>3-</super> Zintl ions were shown to be effective reducing agents in the synthesis of three novel transition metal complexes. The synthesis and crystallographic characterization of the novel [Rh<sub>2</sub>H(PPh<sub>2</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>3</sub>]<super>-</super>, Co<sub>3</sub>(CO)<sub>7</sub><super>3-</super>, and [(C<sub>3</sub>H<sub>7</sub>N<sub>2</sub>O)<sub>3</sub>Ir<sub>4</sub>(CO)<sub>9</sub>]<super>3-</super> ions are reported for the first time and cannot be prepared using traditional reducing agents. Controlled I<sub>2</sub> oxidations of preformed Zintl clusters Pt@Sn<sub>9</sub>Pt(PPh<sub>3</sub>)<super>2-</super> and Sn<sub>9</sub>Ir(cod)<super>3-</super>, give well ordered tin-rich intermetallic nanoparticles of PtSn<sub>4</sub> and Ir<sub>3</sub>Sn<sub>7</sub>, respectively. The intermetallics were characterized by HR-TEM and XRD analysis. Both clusters have strong structural similarities with the final intermetallic, which appears to be an important factor in determining the phase of the resulting intermetallic nanoparticles. Despite the 1:9 (Ir:Sn) atomic ratio of the Sn<sub>9</sub>Ir(cod)<super>3-</super> cluster, ordered Ir<sub>3</sub>Sn<sub>7</sub> nanoparticles were formed instead of the compositionally-similar IrSn<sub>4</sub> phase. PtSn<sub>4</sub> is difficult to prepare by traditional methods and isolate due to the formation of other known Pt-Sn phases, such as PtSn, PtSn<sub>2</sub> and Pt<sub>3</sub>Sn.
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