Mossbauer Spectroscopy of Gold Compounds

A number of publications deal with Au Mossbauer studies of various gold alloys. As the primary goal of this review is directed towards applications of Mossbauer spectroscopy to chemical compounds rather than metallic systems, we present here a brief enumeration of most of the work by giving reference to relevant publications and providing a note concerning the essential points of interest in each case ... 

At the time of their discovery, Mossbauer spectroscopy offered an additional tool to both confirm the quinquevalent oxidation state of gold in these compounds and support the octahedral form predicted for the AuF anion. The 77. 3 keV Ml... 

The data discussed above show that Mossbauer spectroscopy is a valuable adjunct to the list of sporting methods. By specifically probing the gold atom, it supplies information not available by other techniques, and aids the characterization of compounds which are not susceptible to X-ray analysis. 

The oxidation state of the gold present in these compounds is usually determined by MOssbauer spectroscopy (12) but X-ray photoelectron spectroscopy has also been used successfully (l3). The major advantages of the latter technique are simpler sample handling procedures and the elimination of a need for liquid helium coolant, but it requires very careful interpre-... 

If it is possible to dissolve the compound without altering the oxidation states, the classical wet chemical techniques of gravimetry, titrimetry, and electrochemistry can define the oxidation state to a precision of about 0.01 %. For some materials, such as K2Cr207, such dissolution is possible with no measurable change in oxidation state to at least one part in 100,000. For other materials there is at least a partial change in oxidation state on dissolution, and one must resort to instrumental methods. For iron, tin, iodine, gold, and some rare earths Mossbauer spectroscopy is applicable with a precision of about 0.1%. High-resolution X-ray spectra have also been used to determine oxidation state. 

Francium, binary carbide not reported, 11 210 Franck-Condon effect, 16 69 energy, 21 180, 188, 189 envelopes, 16 80, 89, 90 hot bands, 16 90 factors, 32 47 principle, 21 179, 181 vibronic replica, 35 370 frd redon, 38 412, 414 Freeze quench EPR spectroscopy (FQ-EPR), CODH/ACS, 47 318 Fremy s salt, 33 106 Friedel-Crafts reaction, 17 194 cyclophosphazene, 21 65, 66 Frontier molecular orbitals, heteronuclear gold cluster compounds, 39 378-381 Frozen solutions, MOssbauer spectra in studies of, 15 101-103... 

Thanks to the extensive literature on Aujj and the related smaller gold cluster compounds, plus some new results and reanalysis of older results to be presented here, it is now possible to paint a fairly consistent physical picture of the AU55 cluster system. To this end, the results of several microscopic techniques, such as Extended X-ray Absorption Fine Structure (EXAFS) [39,40,41], Mossbauer Effect Spectroscopy (MES) [24, 25, 42,43,44,45,46], Secondary Ion Mass Spectrometry (SIMS) [35, 36], Photoemission Spectroscopy (XPS and UPS) [47,48,49], nuclear magnetic resonance (NMR) [29, 50, 51], and electron spin resonance (ESR) [17, 52, 53, 54] will be combined with the results of several macroscopic techniques, such as Specific Heat (Cv) [25, 54, 55, 56,49], Differential Scanning Calorimetry (DSC) [57], Thermo-gravimetric Analysis (TGA) [58], UV-visible absorption spectroscopy [40, 57,17, 59, 60], AC and DC Electrical Conductivity [29,61,62, 63,30] and Magnetic Susceptibility [64, 53]. This is the first metal cluster system that has been subjected to such a comprehensive examination. 

Single-crystal X-ray crystallography remains the only definitive technique for the structural characterization of heteronuclear gold cluster compounds, although other techniques, in particular Mossbauer, NMR, IR, and fast atom bombardment mass spectroscopies (FABMS), have yielded valuable information, especially concerning the nature of these species in solution. Electron spectroscopy, which has proved to be of great value in the identification of homonuclear gold cluster compounds (210) has received little attention by workers in this area,... 

The following sections summarize the applications of fast atom bombardment mass spectrometry, Mossbauer and NMR spectroscopies, and single-crystal X-ray diffraction studies in the characterization of het-eronuclear gold cluster compounds. 

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