Ag complexes

Although the structure of [SsN] has not been established by X-ray crystallography, the vibrational spectra of 30% N-enriched [SsN] suggest an unbranched [SNSS] (5.22) arrangement of atoms in contrast to the branched structure (Dsh) of the isoelectronic [CSs] and the isovalent [NOs] ion (Section 1.2). Mass spectrometric experiments also support the SNSS connectivity in the gas phase.Many metal complexes are known in which the [SsN] ion is chelated to the metal by two sulfur atoms (Section 7.3.3). Indeed the first such complex, Ni(S3N)2, was reported more than twenty years before the discovery of the anion. It was isolated as a very minor product from the reaction of NiCl2 and S4N4 in methanol. However, some of these complexes, e.g., Cu and Ag complexes, may be obtained by metathetical reactions between the [S3N] ion and metal halides. 

Figure 1. X-ray crystal structure of the monensin-Ag complex (reprinted with permission from the American Chemical Society J. Am. Chem. Soc. 1967, 89, 5737).

The Ag complex 74 catalyses the diboration of internal and terminal aUcenes to 1,2-bis-diboronate esters by bis(catecholato)diboron, (Bcat), in THF at room temperature. Variable conversions (30-90%) were obtained at 5 mol% loading after 60 h. 

The Ag complex 121 in the presence of CuCl H O or CuCOTO CgHg catalyses the allylic alkylations of allyl phosphates by diaUcylzinc reagents with high enantiose-lectivity (Scheme 2.23). A copper complex 122 which is the precursor to the catalytic species was also isolated and structurally characterised (Figs. 2.21 and 2.22) [99]. 

It is essential to know the mode of transport of Au and Ag in ore fluids to consider the factors which control the Ag/Au ratio of native gold and electrum. Many studies on Au and Ag complexes in ore fluids have been conducted and reviewed by several workers (Barnes and Czamanske, 1967 Barnes, 1979 Seward, 1981 Shenberger, 1986). 

According to these previous studies, the most dominant dissolved states of Au and Ag in ore fluids are considered to be bisulfide and chloride complexes, depending on the chemistry of ore fluid (salinity, pH, redox state, etc.). However, very few experimental studies of Au solubility due to chloride complex and Ag solubility due to bisulfide complexes under hydrothermal conditions of interest here have been conducted. Thus, it is difficult to evaluate the effects of these important species on the Ag/Au of native gold and electrum. Other Au and Ag complexes with tellurium, selenium, bismuth, antimony, and arsenic may be stable in ore fluids but are not taken into account here due to the lack of thermochemical data. 

FIG. 6. Plot of log Kx values for Ag+ complexes with unidentate ligands vs log Kx values for corresponding complexes with CH3Hg+. Data at 25°C and ionic strength zero in aqueous solution, from Ref. (11). Ligands are classified as soft ( ) intermediate (O) hard, N-donors (O) hard, O-donors ( ), or F ( ). Formation constant data from Ref. (11). 

Baillet, A., Corbeau, L., Rafidson, R, and Ferrier, D., Separation of isomeric compounds by reversed-phase high-performance liquid chromatography using Ag+ complexation. Application to cis-trans fatty acid methyl esters and retinoic acid photoisomers, /. Chromatogr., 634, 251, 1993. 

Triisopropylsilyloxyfurans were effective nucleophiles for the vinylogous Mannich addition to iminium ions that were formed by Rh2(cap)4-catalyzed oxidation of N-alkyl groups by THYDRO <06JA5648>. A stereoselective addition of 2-trimethylsilyloxyfurans to aryl aldehydes-derived aldimines employing a chiral phosphine/Ag complex as catalyst was developed <06AG(I)7230>. The prototypical example is shown below. 

TABLE 3-8. BINAP-Ag Complex Catalyzed Aldol Reaction... 

The preparation and reactions of metal cluster ions containing three or more different elements is an area with a paucity of results. The metal cyanides of Zn, Cd (258), Cu, and Ag (259) have been subjected to a LA-FT-ICR study and the Cu and Ag complex ions reacted with various reagents (2,256). The [M (CN) ]+ and [M (CN) +11 ions of copper, where n = 1-5, were calculated to be linear using the density functional method. The silver ions were assumed to have similar structures. The anions [M (CN) +1 of both copper and silver were unreactive to a variety of donor molecules but the cations M (CN) H + reacted with various donor molecules. In each case, where reactions took place, the maximum number of ligands added to the cation was three and this only occurred for the reactions of ammonia with [Cu2(CN)]+, [Cu3(CN)2]+, [Ag3(CN)2]+, and [ Ag4(CN)3]+. Most of the ions reacted sequentially with two molecules of the donor with the order of reactivity being Cu > Ag and NH3 > H2S > CO. 

Constants for the formation of some Ag+ complexes in water at 25°C (Andrews and Keefer, 1949)... 

Silver acetate provided access to a new class of compounds ionic organometal-lic polymers based on l,2,4-tiiazolin-3,5-diylidenes [Eq. (12)]. Using just 1 equiv of Ag(OAc) leads to the generation of a conventional bis(NHC)-Ag complex. 

It turns out that the six-membered Cu3( -8)3 rings are paradigmatic units. This type of ring system has been incorporated into current models of metallothioneins [low-molecular-weight proteins which are believed to play a key role in metal metabolism (cf. references in 136)]. The structural chemistry of the Ag complexes seems to be different. Monocyclic Ag(8 ) rings can be linked via bridging ligands as in [(86)Ag(88)Ag(86)] (133) or condensed as in [Ag2(86)2] " (28) (126). 

R = Me or Et). The Ag complexes readily dissociate in solution. Salts of [Ag(CN)2] have been isolated with several bulky quaternary ammonium cations using the double decomposition reaction ... 

Group VI Donors. The thio-oxinato-complex Ag(C9HgNS)2 (54 M = Ag) has been prepared, and its N and S co-ordination confirmed from i.r. data. Solution and powder e.s.r. studies of the compound isolated from the reaction between Ag acetate and the NN-di-n-butyldiselenocarbamate anion confirm that it is a Ag" complex of structure (96). A subsequent single-crystal e.s.r. 

Two X-ray studies of Ag° complexes have appeared. For both [Ag(bipy)-(N03)2] [Ag(2,3-dicarboxy-pyridine)2],2H20, the geometry about the Ag atoms was shown to be a tetragonally distorted octahedron (see Table... 

Although primary batteries of various types based on Agl complexes are at present available commercially, no substantial success has been achieved with rechargeable SBs with Ag compounds conducting at ambient temperature (although Ag/complex/Ag coulometers capable of being cycled many thousands of times are readily available). After a decade of studies, cells based on Agl complexes have not yet been made which are rechargeable to any extent the complex tends to break down into islands of the y-Agl, which is very poorly conductive at room temperature. 

Results similar to those in Table 6 are found for 15-crown-5 and its sulfur analogs (4, 33). Some typical results are given in Table 7 where marked enhancement is seen in the stability of the Ag+ complex relative to that of either the K+ or T1+ complex as sulfur is substituted for oxygen. 

Effect of Ag+ complexation on relative aromaticity in various rings was examined by NICS in two representative cases. Structures and energies of the acetyl pyrene-Ag -pyrene hetero-dimer and acetyl pyrene-Ag -acetyl pyrene homo-dimer complexes were determined with the same model. Interestingly, only sandwich complexes were formed and no stable structures in which the silver ion was not sandwiched between two PAH units could be found. 

CdS/Snj S PV cells have been fabricated where the CdS was deposited by CD and the SnS deposited by a variant of CD where the substrate is dipped first in a solution of one of the ions and then in the other without rinsing in between, as would be the procedure for SILAR (see Sec. 2.11.1) [41]. While the cells showed very low conversion efficiencies, the main emphasis was on Ag-doping of the CdS in order to increase the conductivity and the effect of this doping on the PV cells. An increase in efficiency from 0.03% to 0.08%, mainly as a result of an increase in short-circuit current, was obtained by doping the CdS with Ag. The doping was carried out by an ion exchange process whereby the undoped CdS film was immersed in a solution containing Ag complexed by thiosulphate. 

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