UMD Theses and Dissertations

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Author: search.filters.author.Nalbant-Esenturk, EmrenSubject: search.filters.subject.cluster compounds

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    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.