Silver atom species

Irradiation was therefore carried out on silver doped A-zeo-lites at 77 K and a new silver atom species was detected with a different hyperfine splitting than that of the one observed at 4K. This species is designated as Ag°(A) with an isotropic hyperfine splitting of about 1985 MHz which is very close to that of the free atom value. Species Ag°(A) is the dominant species formed by irradiation at 77 K in all of the A-zeolites studied. In addition, species Ag°(B) is also visible at 77 K. However, upon warming above 77 K species Ag°(B) decays to apparently yield Ag°(A). 

In the presence of substances that react with Ag , the 340 nm absorption decays more rapidly and the rate constant of reaction can be calculated from this decay. It was found in this way that free silver atoms are indeed a strongly reducing species. They reduce Fe to Fe and Cu to Cu (note that these reactions would not occur with the silver atoms at the surface of a compact electrode ) organic compounds containing electrophilic groups such as CICH2COOH or CH3NO2 are reduced by Ag via electron transfer... 

The dinuclear 2 3 species have been characterized in [Ag20u-dppm)3](OTf)2 and [Ag2(p-dppm)3](N03)2 (92), with the silver centers three coordinate by three phosphorus atoms of different dppm ligands.761,768 A tetranuclear species [Ag2(p-02CMe-0,0 )(p-02CMe-0)(p-dppm)]2 has been obtained by reaction of dppm with two equivalents of AgOAc. 762 The reaction of [Ag(Mes)]4 with dppm gives a trinuclear compound [Ag3(dppm-H)3] (93) in which the dppm ligand has been deprotonated with the formation of mesithylene. In the structure, two of the silver centers are three coordinate to three different phosphorus atoms and the other silver atoms is bonded to two carbon atoms.291,292... 

The complexation of anionic species by tetra-bridged phosphorylated cavitands concerns mainly the work of Puddephatt et al. who described the selective complexation of halides by the tetra-copper and tetra-silver complexes of 2 (see Scheme 17). The complexes are size selective hosts for halide anions and it was demonstrated that in the copper complex, iodide is preferred over chloride. Iodide is large enough to bridge the four copper atoms but chloride is too small and can coordinate only to three of them to form the [2-Cu4(yU-Cl)4(yU3-Cl)] complex so that in a mixed iodide-chloride complex, iodide is preferentially encapsulated inside the cavity. In the [2-Ag4(//-Cl)4(yU4-Cl)] silver complex, the larger size of the Ag(I) atom allowed the inner chloride atom to bind with the four silver atoms. The X-ray crystal structure of the complexes revealed that one Y halide ion is encapsulated in the center of the cavity and bound to 3 copper atoms in [2-Cu4(//-Cl)4(//3-Cl)] (Y=C1) [45] or to 4 copper atoms in [2-Cu4(/U-Cl)4(/U4-I)] (Y=I) and to 4 silver atoms in [2-Ag4(/i-Cl)4(/i4-Cl)] [47]. NMR studies in solution of the inclusion process showed that multiple coordination types take place in the supramolecular complexes. 

Several studies have been devoted to adsorption of oxygen on silver surfaces. It has become evident that both molecular and atomic species of adsorbed oxygen exist. It is generally considered that fast dissociative adsorption takes place first and leads to a strongly bonded species, which... 

The occurrence of O2 and O is not excluded, however. Shimizu et al. [291] detected, for the first time, Ag2+ with ESR techniques and postulated the existence of O2. Working with LEED, Bradshaw et al. [60] favoured the hypothesis that O is an active species. Indirect evidence for the presence of O at high temperatures (220° C) was obtained from IR spectra by Force and Bell [116]. It is interesting that preadsorption of chlorine, which is a well known moderator, completely destroys activity when it covers 25% of the surface. Kilty et al. [176] suggested that the first adsorption step is coupled to an ensemble of four adjacent silver atoms, viz. 

To gain more insight into silver-dioxygen species, a matrix isolation study involving cocondensation of Ag atoms with 1602 and 1802 was initiated. Two products were obtained,... 

At first glance, the equation appears to be balanced, because we see the same number of each kind of atom on each side. However, each copper atom has lost two electrons, whereas each silver atom has gained only one. To balance the electrons, we have to balance the charge. We cannot just change Ag+ to Ag2+, because Ag2+ is an entirely different species... 

Silver is often used as a halophile. In the context of six-electron species, the role of silver atoms in carbene, nitrene, and silylene transfer reactions, including aziridination, CH insertion, ring expansion, and silacyclopropanation, has been reviewed.9... 

The aziridination works for both aromatic and aliphatic olefins, including less active linear terminal olefins. Most reactions proceed in good yield at room temperature. The use of ci.v-stilbene at 0°C gives predominately cis aziridine product in about 90 10 cis trails ratio (Table 6.1). The conservation of cis structure suggests that a discrete silver nitrene intermediate is involved in the reaction path. Because of the unique disilver structure and unlikely formation of a silver(III) species, the authors suspect that a bridged nitrene intermediate between the two silver atoms may be responsible for this transformation in which each silver atom donates one electron to the nitrenoid. However, further research is necessary to prove this hypothesis and a fast radical reaction mechanism cannot be eliminated on the basis of current evidence. 

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