Metal clusters, physical characterization

Fierro-Gonzalez, J.C., Kuba, S., Hao, Y. et al. (2006) Oxide- and zeolite-supported molecular metal complexes and clusters physical characterization and determination of structure, bonding, and metal oxidation state, J. Phys. Chem. B, 110, 13326. 

Dr. Rohlfing s research interests include the experimental characterization of transient molecules relevant to combustion processes, linear and nonlinear laser spectroscopies, trace detection of pollutants, molecular beam and mass spectrometric studies of carbon and metal clusters, and vibrational relaxation dynamics. He is the author of approximately 50 peer-reviewed articles, holds membership in the American Chemical Society and the American Physical Society, and is a fellow of the American Association for the Advancement of Science. 

Physical Data [a]o = +143.5° (acetone, c=33.0). The absolute configuration of this reagent (and other arylsulfiny 1 acetic acids) is characterized by two CD Cotton effects which are observed in the presence of the metal cluster [Mo2(OAc)4] in DMSO solution above 300 nm. ... 

Abstract Immobilized metallic and bimetallic complexes and clusters on oxide or zeolite supports made from well-defined molecular organometaUic precursors have drawn wide attention because of their novel size-dependent properties and their potential applications for catalysis. It is speculated that nearly molecular supported catalysts may combine the high activity and selectivity of homogenous catalysts with the ease of separation and robustness of operation of heterogeneous catalysts. This chapter is a review of the synthesis and physical characterization of metaUic and bimetallic complexes and clusters supported on metal oxides and zeohtes prepared from organometaUic precursors of well-defined molecularity and stoichiometry. 

Chapter 4, by Batzill and his coworkers, describes modern surface characterization techniques that include photoelectron diffraction and ion scattering as well as scanning probe microscopies. The chapter by Hayden discusses model hydrogen fuel cell electrocatalysts, and the chapter by Ertl and Schuster addresses the electrochemical nano structuring of surfaces. Henry discusses adsorption and reactions on supported model catalysts, and Goodman and Santra describe size-dependent electronic structure and catalytic properties of metal clusters supported on ultra-thin oxide films. In Chapter 9, Markovic and his coworkers discuss modern physical and electrochemical characterization of bimetallic nanoparticle electrocatalysts. 

Cubic clusters are characterized by an electronic structure which is either molecular or metallic in nature. Accurate measurements of their physical properties may provide some indication of the particle size at which the typical properties of a bulk metal begin to appear. ... 

The first depletion spectra obtained for neutral sodium clusters N = 2-40 were characterized by structureless broad features containing one or two bands. The results were interpreted in terms of collective resonances of valence electrons (plasmons) for all clusters larger than tetramers [2, 52-55]. The analogies between findings for metallic clusters and observations of giant dipole resonances in nuclei have attracted a large attention. Therefore the methods employed in nuclear physics, such as different versions of RPA in connection with the jellium model, have also been applied for studying the optical properties of small clusters. Another aspect was the onset of conductivity in metal-insulator transitions. 

Numerous studies have been devoted to the characterization of platinum clusters in Y zeoUtes using the chemical shift of Xe NMR lines [168-172] or by Xe adsorption isotherms [173]. Details of these studies are beyond the scope of the present review, but it is interesting to note that, following calcination at 573-673 K and reduction at 573-673 K, the nuclearity of metal clusters was found to be between 13 and 55 (in most cases between 20 and 40), and this is in reasonable agreement with the characterization of particle size or coordination numbers obtained by physical methods such as TEM, SAXS, RED, and EXAFS [15,76,90,150]. 

The Characterization and Properties of Small Metal Particles. Y. Takasu and A. M. Bradshaw, Surf. Defect. Prop. Solids p. 401 1978). 2. Cluster Model Theory. R. P. Messmer, in "The Nature of the Chemisorption Bond G. Ertl and T. Rhodin, eds. North-Holland Publ., Amsterdam, 1978. 3. Clusters and Surfaces. E. L. Muetterties, T. N. Rhodin, E. Band, C. F. Brucker, and W. R. Pretzer, Cornell National Science Center, Ithaca, New York, 1978. 4. Determination of the Properties of Single Atom and Multiple Atom Clusters. J. F. Hamilton, in "Chemical Experimentation Under Extreme Conditions (B. W. Rossiter, ed.) (Series, "Physical Methods of Organic Chemistry ), Wiley (Interscience), New York (1978). 

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