Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA.
Angewandte Chemie International Edition (Impact Factor: 13.73). 05/2004; 43(16):2132-4. DOI:10.1002/anie.200353287
Source: PubMed
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    ABSTRACT: Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later. Their redox chemistry is even younger, just about ten years old, but despite this short history these deltahedral clusters ions E9(n-) (E = Si, Ge, Sn, Pb; n = 2, 3, 4) have already shown interesting and diverse reactivity and have been at the forefront of rapidly developing and exciting new chemistry. Notable milestones are the oxidative coupling of Ge9(4-) clusters to oligomers and infinite chains, their metallation, capping by transition-metal organometallic fragments, insertion of a transition-metal atom at the center of the cluster which is sometimes combined with capping and oligomerization, addition of main-group organometallic fragments as exo-bonded substituents, and functionalization with various organic residues by reactions with organic halides and alkynes. This latter development of attaching organic fragments directly to the clusters has opened up a new field, namely organo-Zintl chemistry, that is potentially fertile for further synthetic explorations, and it is the step-by-step procedure for the synthesis of germanium-divinyl clusters described herein. The initial steps outline the synthesis of an intermetallic precursor of K4Ge9 from which the Ge9(4-) clusters are extracted later in solution. This involves fused-silica glass blowing, arc-welding of niobium containers, and handling of highly air-sensitive materials in a glove box. The air-sensitive K4Ge9 is then dissolved in ethylenediamine in the box and then alkenylated by a reaction with Me3SiC≡CSiMe3. The reaction is followed by electrospray mass spectrometry while the resulting solution is used for obtaining single crystals containing the functionalized clusters [H2C=CH-Ge9-CH=CH2](2-). For this purpose the solution is centrifuged, filtered, and carefully layered with a toluene solution of 18-crown-6. Left undisturbed for a few days, the so-layered solutions produced orange crystalline blocks of [K(18-crown-6)]2[Ge9(HCCH2))2]•en which were characterized by single-crystal X-ray diffraction. The process highlights standard reaction techniques, work-up, and analysis towards functionalized deltahedral Zintl clusters. It is hoped that it will help towards further development and understanding of these compounds in the community at large.
    Journal of Visualized Experiments 01/2012;
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    ABSTRACT: A set of silver-doped lead Zintl anions, Ag@Pb(n)(-) (n = 5-12), have been studied using photoelectron velocity-map imaging spectroscopy and quantum chemical calculation. The structures of Ag@Pb(n)(-) (n = 7-9, 11) built upon a square pyramid base, hitherto not considered, were assigned. Overall agreement between the experimental and calculated photoelectron spectra as well as vertical detachment energies allows for structural evolution to be established. The silver atom prefers to stay outside in the n ≤ 6 clusters and intends to be encapsulated by the lead atoms in n > 6. A stable endohedral cage with bicapped square antiprism structure is formed at n = 10, the endohedral structure of which persists for the larger clusters. Especially, these Ag@Pb(n)(-) anions have been found to undergo a transition between square pyramid and pentagonal pyramid molecular structures at n = 11.
    The Journal of Chemical Physics 08/2012; 137(6):064318. · 3.16 Impact Factor
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    ABSTRACT: A combination of anion photoelectron spectroscopy and density functional theory calculations has elucidated the geometric and electronic structure of gas-phase endohedral Pt/Pb cage cluster anions. The anions, and were prepared from "preassembled" clusters generated from crystalline samples of [K(2,2,2-crypt)](2)[Pt @ Pb(12)] that were brought into the gas phase using a unique infrared desorption/photoemission anion source. The use of crystalline [K(2,2,2-crypt)](2)[Pt @ Pb(12)] also provided access to K[Pt @ Pb(n)](-) anions in the gas phase (i.e., the K(+) salts of the anions). Anion photoelectron spectra of , , and K[Pt @ Pb(12)](1-) are presented. Extensive density functional theory calculations on and provided candidate structures and anion photoelectron spectra for and . Together, the calculated and measured photoelectron spectra show that and endohedral complexes maintain their respective D(4d) and slightly distorted I(h) symmetries in the gas phase even for the charge states with open shell character. Aside from the fullerenes, the endohedral complex is the only bare cluster that has been structurally characterized in the solid state, solution, and the gas phase.
    Proceedings of the National Academy of Sciences 09/2011; 108(36):14757-62. · 9.74 Impact Factor