UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
2 results
Search Results
Item Homoleptic Naked Clusters of Endohedral Zintl Ions(2006-03-31) Nalbant-Esenturk, Emren; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoclusters are of interest because of their remarkable catalytic properties and their application in nanotechnology fields. There is a strong preference toward bimetallic systems due to their superior catalytic properties compare to monometallic systems. Synthetic protocols are developed by using polyatomic main group clusters (Zintl ions) for making new bimetallic nano-catalysts. In this study, new, free standing, transition metal stabilized Zintl ions have been isolated. They are promising candidates to be used both in nanotechnology and heterogeneous catalysis. [M@Pb<sub>12</sub>]<sup>2-</sup> (M = Ni, Pd, Pt) are the <em>first isolated</em> free-standing centered icosahedra without any attendant of ligands. The anions contain naked Pb<sub>12</sub> icosahedra clusters encapsulating Group 10 transition metals and posses near perfect I<sub>h</sub> point symmetry. These endohedral naked metal clusters have nontraditional spherical aromatic electronic structures. They are the smallest members of the nanoparticle growth sequence, M<sub>13</sub> (centered icosahedra), with hcp lattices. Their positive chemical shifts in <sup>207</sup>Pb NMR spectra contradict theoretical chemical shift calculations of isostructural aromatic clusters. A new type of Zintl ion, [Ni@Pb<sub>10</sub>]<sup>2-</sup>, has also been synthesized. The anion contains Ni atom centered in a closo-Pb<sub>10</sub><sup>2-</sup> bicapped square antiprism, and possesses virtual D<sub>4d</sub> point symmetry. It is the first isolated ten atom, homoatomic naked Zintl ion cluster. The Pt and Pd analogs, and non-metallated Pb<sub>10</sub> and Pb<sub>12</sub> clusters have also been observed in the gas phase by LDI-TOF-MS. NMR spectroscopy was used to investigate unusual dynamic behaviors of the one focus [Ni@Pb<sub>10</sub>]<sup>2-</sup> and two focus [Ni<sub>2</sub>Sn<sub>17</sub>]<sup>4-</sup> anions and both demonstrated surprising global atomic mobility. The latter has a capsule like structure having central Sn atom with coordination number of eight. This extraordinary high coordination of the central Sn is more akin to solid state compounds. The [Ge<sub>9</sub>Ni<sub>2</sub>(PPh<sub>3</sub>)]<sup>2-</sup> anion is the new example of Zintl ion, which do not adopt Wadian type structure. Another Ni-Ge system with exciting structure, [Ni<sub>6</sub>Ge<sub>13</sub>(CO)<sub>5</sub>]<sup>4-</sup> is also isolated. The anion has interpenetrating biicosahedral structure which is unique to Zintl ion chemistry. The potential interconversion of [Ge<sub>9</sub>Ni<sub>2</sub>(PPh<sub>3</sub>)]<sup>2-</sup> and [Ni<sub>6</sub>Ge<sub>13</sub>(CO)<sub>5</sub>]<sup>4-</sup> have been investigated through ESI-MS studies.Item Synthesis and Characterization of Binary Clusters to Controllable Binary Nanoparticles "The New Role of Zintl Anions"(2004-10-27) Moses, Melanie Jean; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Zintl anions are best described as polyatomic main group clusters (i.e. E73-; E = P, As, Sb) with structures characteristic of isoelectronic clusters (i.e. hydrocarbon and borohydride clusters). Combining these main group clusters and transition-metal precursors (Ni(COD)2; COD = cyclooctadiene, and Pd(PCy3)2; PCy3 = tricyclohexyl phosphine) with very labile ligands allows for the isolation of novel binary molecular clusters. The freedom these structures experience due to the absence of organic ligands lends itself to the very unique structure growth the binary clusters exhibit. Direct oxidation of these binary molecular clusters results in the formation of binary phases (i.e. PdAs2, NiAs, NiAs2). More control of the phase-specific binaries obtained can be achieved by controlling the reaction of the precursors, eliminating the need to isolate the clusters. Binary nanoparticles are in the forefront of heterogeneous catalyst development and application, making this an area of intense investigation. Structural characteristics of the binary clusters, [As@Ni12@As20]3-, [(Ni2Sb2)(Sb7)2]4-, [Ni5Sb17]4-, [Pd7As16]4- and [Pd2(E7)2]4- (E = P, As), and evidence for the formation of phase-specific binary nanoparticles (Ni5As2, Ni11As8, NiAs and NiAs2) under very mild conditions will be presented.