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Robert R. Ryan

Bio: Robert R. Ryan is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Crystal structure & Coordination complex. The author has an hindex of 33, co-authored 117 publications receiving 3266 citations.


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TL;DR: In this article, the first isolable transition-metal complexes containing a coordinated dihydrogen molecule was reported, characterized by a variety of spectroscopic and structural methods to possess n/sup 2/bonded hydrogen.
Abstract: Reported were the first examples of isolable transition-metal complexes containing a coordinated dihydrogen molecule, characterized by a variety of spectroscopic and structural methods to possess n/sup 2/-bonded hydrogen. The dihydrogen ligand is symmetrically coordinated in an n/sup 2/ mode with average tungsten-hydrogen distances of 1.95 (23) angstroms (x-ray) and 1.75 angstroms (neutron, ..delta..F). The H-H separation is 0.75 (16) angstrom (x-ray) and 0.84 angstroms (neutron, ..delta..F), slightly larger than that obtained from free H/sub 2/ (0.74 angstroms). The H/sub 2/ ligand axis is approximately parallel to the trans phosphorous-phosphorus direction. Vibrational spectra of solid samples of the H/sub 2/, D/sub 2/, and HD forms (M = W) are consistent with coordination of molecular H/sub 2/. The H/sub 2/ complexes are significant in that they may represent an arrested form of oxidative addition of H/sub 2/ to metals. 1 table (DP)

625 citations

Journal ArticleDOI
TL;DR: Since these molecules add dihydrogen to form stable eta/sup 2/-H/sub 2/ complexes, they afford an unprecedented opportunity to observe both H-H and C-H bond activation at a single metal center.
Abstract: The synthesis, reactivity, and molecular structures of coordinatively and electronically unsaturated complexes M(CO)/sub 3/(PR/sub 3/)/sub 2/ (M = Mo, W; R = Cy, i-Pr) are described. Ligands that bind reversibly to W(CO)/sub 3/(PCy/sub 3/)/sub 2/ include H/sub 2/, N/sub 2/, C/sub 2/H/sub 4/, H/sub 2/O, ROH, and thiophene; irreversibly bound ligands are MeCN, pyridine, NH/sub 3/, CyNH/sub 2/, and PR/sub 3/. The structures of W(CO)/sub 3/(PCy/sub 3/)/sub 2/ and W(CO)/sub 3/(P(i-Pr)/sub 3/)/sub 2/ involve incipient intramolecular oxidative addition of a distal phosphine C-H bond to the metal. The three-center M...H-C interaction in W(CO)/sub 3/(PCy/sub 3/)/sub 2/ has W-H(11a)-C(11) = 127.6/sup 0/, W-C(11) = 2.945 (6) A, and W-H(11a) approx. 2.27 A. Crystal data for W(CO)/sub 3/(PCy/sub 3/)/sub 2/ are the following: space group P1, a = 10.300 (1) A, b = 12.675 (2) A, c = 15.473 (1) A, ..cap alpha.. = 91.44 (1)/sup 0/, ..beta.. = 90.37 (1)/sup 0/, ..gamma.. = 103.99 (1)/sup 0/, Z = 2, rho(calcd) = 1.34 g cm/sup -3/, R = 0.025, 6211 reflections. Crystal data for W(CO)/sub 3/(P-i-Pr/sub 3/)/sub 2/ are the following: P2/sub 1//m, a = 8.425 (1) A, b = 13.375 (2) A, c = 12.039 (2) A, ..beta.. = 109.58 (1)/supmore » 0/, Z = 2, rho(calcd) = 1.53 g cm/sup -3/, R = 0.034, 2212 reflections. Since these molecules add dihydrogen to form stable eta/sup 2/-H/sub 2/ complexes, they afford an unprecedented opportunity to observe both H-H and C-H bond activation at a single metal center.« less

98 citations

Journal ArticleDOI
TL;DR: In this article, the rate constants for solubilization of hydrous plutonium oxide by siderophores enterobactin and desferrioxamine Β and selected carboxylates, amino polycarboxylate, and catecholate ligands were determined.
Abstract: Accurate predictions of actinide and fission product migration in the geosphere are critically dependent on identification of the biological, chemical and physical processes which affect actinide mobility in soil and water. Siderophores are low molecular weight iron chelators produced by microbes in response to low availability of soluble iron. Because of the similarities between iron(III) and tetravalent actinides, and the prevalence of siderophore-producing microbes in soil, there is strong likelihood that siderophores may also bind actinides, thereby influencing their mobility in the environment. In order to begin to assess the potential importance of siderophore-mediated actinide mobility, we have determined rate constants for solubilization of hydrous plutonium oxide by the siderophores enterobactin and desferrioxamine Β and selected carboxylate, amino polycarboxylate, and catecholate ligands. The measured rate constants for solubilization of insoluble actinide oxides show that siderophores are extremely effective in solubilizing actinides; on a per molecule basis, enterobactin is ~ 1 0 3 times more effective than the other chelators tested in increasing the rate of solubilization of hydrous plutonium oxide. Notably, ferric-siderophore complexes are more effective in solubilizing actinide oxides than the siderophores in the absence of iron. These results suggest that siderophores have the potential to mobilize actinides in the environment.

95 citations

Journal ArticleDOI
TL;DR: The scheelite (CaWO 4 ) structure is confirmed in this paper, where LiYF 4 is located at a 4 site with four equidistant fluoride ions and Yttrium is in an eightfold coordination typical for rare earth ions.
Abstract: Lithium yttrium tetrafluoride, LiYF 4 , M r =171.8, tetragonal, I4 4 /a, a=5.164 (1), c=10.741 (2) A, V=286.5 (1) A 3 , Z=4, D x = 3.99 g cm -3 , λ(Mo Kα)=0.7107 A, μ=204 cm -1 , F(000)=312, T=295 K, R=0.015 for 156 unique observed [F>4σ(F)] reflections. The scheelite (CaWO 4 ) structure is confirmed. Lithium is located at a 4 site with four equidistant fluoride ions. Yttrium is in an eightfold coordination typical for rare-earth ions

91 citations


Cited by
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Journal ArticleDOI
TL;DR: The Gibbs free energies, enthalpies and entropies of 42 dissolved uranium species and 30 uranium-bearing solid phases have been critically evaluated from the literature and estimated when necessary for 25°C.

2,019 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that carbon-hydrogen bonds may act as ligands to transition metal centers forming covalent CH⇀M systems in which the H group donates two electrons to the metal.

1,098 citations

Journal ArticleDOI
TL;DR: The perspective taken herein will allow C-H oxidation reactions to be more readily incorporated into synthetic planning and to emphasize chemoselectivity imposed by the nature of the substrate.
Abstract: C-H oxidation has a long history and an ongoing presence in research at the forefront of chemistry and interrelated fields. As such, numerous highly useful articles and reviews have been written on this subject. Logically, these are generally written from the perspective of the scope and limitations of the reagents employed. This Minireview instead attempts to emphasize chemoselectivity imposed by the nature of the substrate. Consequently, many landmark discoveries in the field of C-H oxidation are not discussed, but hopefully the perspective taken herein will allow C-H oxidation reactions to be more readily incorporated into synthetic planning.

1,070 citations

Journal ArticleDOI
TL;DR: The synthetic approaches employed thus far for producing frameworks with exposed metal sites are reviewed, the hydrogen uptake capacities and binding energies in these materials are summarized, and results from experiments used to probe independently the metal-hydrogen interaction in selected materials will be discussed.
Abstract: Owing to their high uptake capacity at low temperature and excellent reversibility kinetics, metal–organic frameworks have attracted considerable attention as potential solid-state hydrogen storage materials. In the last few years, researchers have also identified several strategies for increasing the affinity of these materials towards hydrogen, among which the binding of H2 to unsaturated metal centers is one of the most promising. Herein, we review the synthetic approaches employed thus far for producing frameworks with exposed metal sites, and summarize the hydrogen uptake capacities and binding energies in these materials. In addition, results from experiments that were used to probe independently the metal–hydrogen interaction in selected materials will be discussed.

1,060 citations