Communication Theory and Storage and Retrieval Systems

Taube, Mortimer

doi:10.21236/ad0093970

Cited by 5 publications

(7 citation statements)

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“…It should be noted that work in progress in Professor Taube 1 s laboratory (37) suggests that previous estimates of the rate of this exchange are probably considerably too low, so that the anomaly may be only an apparent one.…”

Section: Parameters Of Electron-transfer Kinetics 319mentioning

confidence: 96%

Parameters of Electron-Transfer Kinetics

Hush

1982

Mechanistic Aspects of Inorganic Reactions

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Over the last two decades, there has been a considerable increase in experimental information about the rates of electron transfer processes, particularly in solution in ionizing solvents. The main features (enthalpies, free energies and entropies of activation) of a large class of these reactions have been broadly understood for about the same length of time. It is interesting to note that the results of very early calculations of outer-sphere reaction rates and their tempera ture dependence frequently agree with recent more detailed estimates. In order to assess the appli cability of different approaches, and thus to discriminate between them, it is desirable to have as much detailed information as possible about the relevant basic parameters. These include, for example, electron coupling or overlap energies, electron-phonon coupling strengths, vibrational frequencies, and spin coupling data. A brief survey is given of the types of experiment which may provide this information. With such data, discussions on matters such as the applicability of Golden Rule perturbation approaches, electronic adiabaticity, the role of nuclear tunnelling, etc., can be put on firmer ground, and some of the outstanding theoretical issues awaiting reso lution are outlined.The theory of homogeneous electron transfer processes, as well as of the closely-related electron exchanges with metallic electrodes, has been the subject of considerable study.The proposal by Hush and by Marcus that these processes are, for simple systems, either usually electronically adiabatic or 0097-6156/82/0198-0301$09.00/0

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Section: Parameters Of Electron-transfer Kinetics 319mentioning

confidence: 96%

Parameters of Electron-Transfer Kinetics

Hush

1982

Mechanistic Aspects of Inorganic Reactions

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“…Most synthetic work and the related experimental characterization of these η 2 -H 2 osmium complexes have been carried out by Li and Taube, but thus far the H−H distance has been experimentally established for one complex only, namely, [Os(en) 2 CH 3 COO(η 2 -H 2 )] + (en = ethylenediamine), using X-ray and neutron diffraction methods. However, the series [Os(NH 3 ) 4 L z (η 2 -H 2 )] ( z +2)+ , where L z is a trans ligand (L z = (CH 3 ) 2 CO, H 2 O, CH 3 COO - , Cl - , H - , C 5 H 5 N, and CH 3 CN), has been the subject of a careful quantum chemical study by Craw, Bacskay, and Hush (referred to as CBH hereafter) which addressed the problems of molecular geometries, binding energies of H 2 in the complexes, and spin−spin coupling constants J HD , as well as elucidating the bonding mechanism.…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical Study of the Properties of Molecular Hydrogen Complexes of Osmium(II): A Comparison of Density Functional and Conventionalab InitioMethods

1996

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The geometries of [Os(NH3)4L z (η2-H2)]( z +2)+ complexes, where molecular hydrogen is trans to the Lz ligand, have been calculated using density functional theory (DFT) and compared with the results of MP2 calculations. The quality of agreement between the DFT and MP2 geometries is found to be dependent on the trans ligand L z . When L z = acetone, water, acetate, and chloride, the agreement between the DFT and MP2 calculations is generally reasonable, and for the L z = acetate complex, the DFT and the MP2 predictions are in acceptable agreement with the experimental geometry. When L z = hydride, pyridine, acetonitrile, cyanide, hydroxylamine, and ammonia, the DFT calculations predict a much shorter H−H bond length and slightly longer Os−H distances when compared with the MP2 values. As the potential energy surfaces are very flat with respect to the H−H stretch, the differences between the DFT and MP2 geometries correspond to energy differences of approximately 3 kcal mol-1 when calculated at the same level of theory. The differences between the DFT and MP2 predictions appear to correlate with the properties of the trans ligand L z , in particular its σ-donor and π-acceptor/donor properties. The DFT predictions of the Os−H2 interaction energy are consistently smaller by ∼25% than the corresponding MP2 values, but the agreement is much better in the case of the Os−L z bond. Solvation by water, estimated by a self-consistent reaction field technique, is found to have little effect on the binding of H2, while significantly reducing the binding energies of the trans ligands, especially those that are charged. The integrated atomic charges for the dihydrogen ligand, obtained by the atoms in molecules method, are slightly negative, while Os varies between 1.01 and 1.81. The DFT calculations generally predict both species to be somewhat closer to neutral than those obtained at the MP2 level; this is consistent with the notion that DFT predicts stronger H−H but weaker Os−H bonding than MP2, i.e., less donation by Os into the antibonding σ* MO of H2.

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“…Acknowledgments. The support of a Camille and Henry Dreyfus Foundation Teacher-Scholar Grant (1974-1979) is gratefully acknowledged. Thanks are also due to the Youngstown State University Computer Center for continued support and assistance, and to Dr. Irwin Cohen for his comments and suggestions.…”

mentioning

confidence: 99%

Intramolecular electron transfer from pentacyanoferrate(II) to pentaamminecobalt(III) mediated by various 4,4'-bipyridines

Jwo¹,

Gaus²,

Haim³

1979

J. Am. Chem. Soc.

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The reactions of Fe(CN)50Hz3-with Co(NH3)sL3+ ( L = bis(4-pyridyl)methane, bis(4-pyridyl)ethane, bis(4-pyridyl)propane, bis(4-pyridyl)ethylene, and bis(4-pyridyl) ketone) produce binuclear complexes (NC)5Fe'1LCo1'1(NH3)s that exhibit iron t2g to ligand K* charge transfer bands at (same order) 370, 365, 360, 500, and 555 nm. Comparison of these values with those for the corresponding Fei1(CN)sL3-complexes (370, 365, 360, 460, and 520 nm) suggests that the electron-withdrawing effect of the Co(ll1) moiety attached to the remote N is transmitted to the ring adjacent to the Fe(ll) via T interactions, and that saturated hydrocarbon groups connecting the two pyridine rings insulate electronically the iron and cobalt centers. Rate constants for the formation and dissociation of the binuclear complexes have been measured and a dissociative mechanism is clearly indicated by the LFER of slope -1.0 between rate constants and equilibrium constants for the formation reactions. The rateconstants for intramolecular electron transfer from Fe(ll) to Co(l1l) in the binuclear complexes have been measured. At 25 "C, p = 0. I0 M, the values are (same order of ligands) <0.6 X and

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Communication Theory and Storage and Retrieval Systems

Cited by 5 publications

References 0 publications

Parameters of Electron-Transfer Kinetics

Parameters of Electron-Transfer Kinetics

Quantum Chemical Study of the Properties of Molecular Hydrogen Complexes of Osmium(II): A Comparison of Density Functional and Conventionalab InitioMethods

Intramolecular electron transfer from pentacyanoferrate(II) to pentaamminecobalt(III) mediated by various 4,4'-bipyridines

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