Electron spin resonance spectroscopy metal studies

Electron Spin Resonance Spectroscopy. Several ESR studies have been reported for adsorption systems [85-90]. ESR signals are strong enough to allow the detection of quite small amounts of unpaired electrons, and the shape of the signal can, in the case of adsorbed transition metal ions, give an indication of the geometry of the adsorption site. Ref. 91 provides a contemporary example of the use of ESR and of electron spin echo modulation (ESEM) to locate the environment of Cu(II) relative to in a microporous aluminophosphate molecular sieve. 

It is interesting to note that the catalysts that show good selectivities at the higher temperatures generally do not contain easily reducible metal ions, such as V, Mo, or Sb. Many of the catalysts for the lower-temperatures operation, on the other hand, contain these reducible cations. In a study using a Li-Mg oxide, it was established that gas-phase ethyl radicals could be generated by reaction of ethane with the surface at about 600°C (17). These radicals could be trapped by matrix isolation and identified by electron spin resonance spectroscopy. 

There is apparently only one report of the dissolving metal reduction of thioketones thiobenzophe-none (107) has been reduced with excess Na-THF to give dianion (108), which on acidification gave thiol (109). The thiol was not isolated, but was oxidized with iodine to give the corresponding disulfide in 65% overall yield. The mechanism of the reduction is suggested to be the sequential addition of two electrons to the thiocarbonyl, which was confirmed by electron spin resonance spectroscopy studies of the intermediate thioketyl, and trapping dianion (108) with a variety of electrophiles. ... 

Mendt M, Jee B, Stock N et al (2010) Structural phase transitions and thermal hysteresis in the metal-organic framework compound MlL-53 as studied by electron spin resonance spectroscopy. J Phys Chem C 114 19443-19451... 

It should be noted that there is an important distinction to be made between the hexamethylacetone-sodium ion-quartet and the situation described by the original G.F.F. theory. In the G.F.F. theory it was assumed that the solvent dependence of hyperfine splitting constants is to be attributed to modifications in spin density distributions, whereas for the ion-quartet the spin density distribution is the same in tetrahydro-furan and in methyltetrahydrofuran. The variation in with solvent must be due to variation in the geometry of the ion-quartet, which will in turn vary the efficiency of the mechanism whereby spin is transferred to the alkali metal nucleus. Thus, in this case, the solvent dependence is to be attributed to variations in Q rather than p. The situation is common in the study of ionic association through electron spin resonance spectroscopy and has thwarted many attempts at quantitative descriptions of the effect of solvation upon such association until the geometry of the ionic associate in solution is firmly established it is not too rewarding to discuss how the spectrum varies with change in solvent. 

Ligand complexation of vanadium by iV-(L-l-carboxyethyl)-7V-hy-droxy-L-alanine in vivo by fruit bodies of Amanita muscaria produces the blue complex, amavadin (571) 69, 418). The structure and stereochemistry of this most unusual compound has been proved by total synthesis 418), and the valence state of the metal in amavadin has been studied by electron spin resonance spectroscopy 287). 

The real power of electron spin resonance spectroscopy for structural studies is based on the interaction of the impaired electron spin with nuclear spins. This interaction splits the energy levels and often allows determination of the atomic or molecular structure of species containing unpaired electrons, and of the ligation scheme around paramagnetic transition-metal ions. The more complete Hamiltonian is given in equation 2 for a species containing one unpaired electron, where the summations are over all the nuclei, n, interacting with the electron spin. 

Electron Paramagnetic Resonance Spectroscopy (EPR), or Electron Spin Resonance (ESR), for studying paramagnetic properties of crystals, including metal ions, free radicals, and organometaUics. 

The title Spectroscopy in Catalysis is attractively compact but not quite precise. The book also introduces microscopy, diffraction and temperature programmed reaction methods, as these are important tools in the characterization of catalysts. As to applications, I have limited myself to supported metals, oxides, sulfides and metal single crystals. Zeolites, as well as techniques such as nuclear magnetic resonance and electron spin resonance have been left out, mainly because the author has little personal experience with these subjects. Catalysis in the year 2000 would not be what it is without surface science. Hence, techniques that are applicable to study the surfaces of single crystals or metal foils used to model catalytic surfaces, have been included. 

Prereactive behaviors were identified very early and an impressive series of examples was listed in a book by Klabunde in 1980 [266]. Electron spin resonance (ESR) studies reveal that in low-temperature matrices electron-transfer reactions are blocked as a rule and most, if not all, charge-transfer complexes involved in standard gas-phase harpoon reactions have been stabilized and observed in matrices. The ESR spectra of these systems revealed nearly complete electron transfer. Similar conclusions have also been drawn from infrared spectroscopy. For example, outside the field of alkali metal atoms, evidence of an AHNO complex has been obtained by this technique [267]. It should not be thought that every metal atom is able to make charge transfer with every molecule. For example, no indication exists of a charge transfer between Cu and NO in an argon matrix [268]. 

A number of transition metal nuclei can be studied by Mossbauer techniques (e.g., Fe, Ni, Ru, W, Os, Ir, and Pt). Of these, only Ir, Ru, and Fe have been used to study nitrosyl bonding. The most detailed studies have been on the well-known iron complexes [Fe(CN)5(NO)] - (87. 89) and [Fe(NO)(dtc)z] (88-90) (dtc is N,N-dialkyldithiocarbamato). In the latter, high-spin/low-spin equilibria can be followed by Fe Mossbauer spectroscopy, and the Mossbauer parameters agree well with data from electron spin resonance (ESR) spectroscopy in determining the ground states of these complexes. 

A large number of paramagnetic transition metal nitrosyl complexes have been studied using electron spin resonance (ESR) spectroscopy. Information on the electronic ground state can be derived from the g-value and the hyperfine coupling constants, and many [MLslNO)]" (see Table IV) and nitrosyl porphyrin complexes (99) have been studied in this way with a view to understanding their electronic structures. 

Electron-spin resonance (e.s.r.) spectroscopy is a technique for the study of species containing one or more unpaired electrons. The scope of the method includes the detection and characterization of some transition-metal ions, simple molecules and ions (e.g. O2, NO, NOg, COi"), and organic radicals, including biradicals and triplet states. 

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