Silver® complexes

The X-ray structure of the monoferrocenyl-silver complex is shown in Fig. 7-71 [195]. The cryptand-like cavity of the peripheral tetraoxa-dizazadecane ring is able to accomodate one Ag ion, but it is thought that a direct Fe-Ag interaction also occurs. The cyclopentadienyl rings of the ferrocene portion are tilted by 10°. 

As illustrated in Fig. 7-72, complexation of silver ions in acetonitrile solution causes the one-electron oxidation of the ferrocene fragment to shift anodically by 

282 mV with respect to that of the original ferrocene molecule (E° = 0.22 V). It 

A minor shift in redox potential is caused by silver ion complexation of the diferrocenyl-monocryptand complex. In fact, the silver-free ferrocene ligand undergoes a single-step two-electron oxidation at E° = -1-0.39 V in MeCN. On incorporation of silver ion, the two-electron redox change occurs at ° = -1-0.50 V. 

282 mV with respect to that of the original ferrocene molecule (E° = +0.22 V). It is likely that such an increase in redox potential, which is one of the highest so far reported, may arise from the diminished electron density on the iron(ii) center caused by the Fe - Ag interaction [195]. 

Other X-ray characterized silver-ferrocenyl complexes include Fef(r/ -C5H3)(l-CH,NMe2)(2-Ag)] 4 [196], [Fe( j -C5H4PPh2)3]Ag2(CeH5C02) 

The existence of a solid 1 1 and a liquid 2 1 toluene-Cu(AlCl4) molecular complex has been shown by vapor pressure-phase composition studies (2S7). The results indicated that the toluene molecules in the 2 1 complex are not as strongly bonded to the Cu(I) atom as in the 1 1 complex. The toluene could be removed from the 1 1 complex by heating at 50° to 60°C at a pressure of 10 mm, yielding pure CUAICI4. 

The crystalline air-sensitive complex (CgHe)[Cu(0S02CFg)]2 has been isolated from the reaction of trifluoromethanesulfonicanhydride with Cu(I) oxide in benzene (38J). The complex was stable to 100°C when heated in a sealed evacuated tube, the benzene being released quantitatively only above 120°C. The structure has been determined and consists of infinite chains of Cu(S03CF3) units cross-linked in sheets by the benzene molecules (94). The benzene-Cu(I) coordination is shown in (XLI). The structure was not sufficiently well-resolved to observe 

The existence of donor-acceptor complexes between aromatic molecules and Ag(I) has been known for some time 10-12), Many arene-Ag(I) complexes have been obtained from silver perchlorate and an aromatic hydrocarbon. Complexes containing various ratios of aromatic hydrocarbon to silver perchlorate have been observed including 1 1, 1 2, 2 1, and 1 4 complexes (see Table VI). Crystal structures have been obtained for several of the complexes. The 1 1 complex (CeHg)Ag(C104) (XLIII) consists of chains of alternating benzene 

Ag(C104) (404) and (cyclohexylbenzene)2Ag(C104) 199, 200). In the 1 4 complex, (anthracene)[Ag(C104)]4 H2O (XLVII), two silver atoms are coordinated to each of the outer rings 201). Similar coordination was observed for (naphthalene)[Ag(C104)]4 4H20 201). 

Anhydrous AgBF4 has also been reported to form complexes with aromatic hydrocarbons, and these are generally more stable than the AgC104 analogs (J40). 

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The preparation of a series of transition metal complexes (Co. Ni. Pd. Pt, Ir. Au. Cu. Ag) with ambident anion (70) and phosphines as ligands has been reported recently (885). According to the infrared and NMR spectra the thiazoline-2-thione anion is bounded through the exocyclic sulfur atom to the metal. The copper and silver complexes have been found to be dimeric. 

Trilialophenols can be converted to poly(dihaloph.enylene oxide)s by a reaction that resembles radical-initiated displacement polymerization. In one procedure, either a copper or silver complex of the phenol is heated to produce a branched product (50). In another procedure, a catalytic quantity of an oxidizing agent and the dry sodium salt in dimethyl sulfoxide produces linear poly(2,6-dichloro-l,4-polyphenylene oxide) (51). The polymer can also be prepared by direct oxidation with a copper—amine catalyst, although branching in the ortho positions is indicated by chlorine analyses (52). 

Silver and sulfur combine even in the cold to form silver sulfide. The tendency of silver to tarnish is an example of the ease with which silver and sulfur compounds react. PoHshes that contain silver complexing agents, such as chloride ion or thiourea, are used to remove silver tarnish. 

Silver ions form a number of complexes with both TT-bonding and non-TT-bonding ligands. Linear polynuclear complexes are known. The usual species are AgL and AgL2, but silver complexes up to AgL have been identified. Many of these complexes have commercial appHcation. 

To minimize the formation of fuhninating silver, these complexes should not be prepared from strongly basic suspensions of silver oxide. Highly explosive fuhninating silver, beheved to consist of either silver nitride or silver imide, may detonate spontaneously when silver oxide is heated with ammonia or when alkaline solutions of a silver—amine complex are stored. Addition of appropriate amounts of HCl to a solution of fuhninating silver renders it harmless. Stable silver complexes are also formed from many ahphatic and aromatic amines, eg, ethylamine, aniline, and pyridine. 

Sulfur Complexes. Silver compounds other than sulfide dissolve in excess thiosulfate. Stable silver complexes are also formed with thiourea. Except for the cyanide complexes, these sulfur complexes of silver are the most stable. In photography, solutions of sodium or ammonium thiosulfate fixers are used to solubilize silver hahdes present in processed photographic emulsions. When insoluble silver thiosulfate is dissolved in excess thiosulfate, various silver complexes form. At low thiosulfate concentrations, the principal silver species is Ag2(S203) 2j high thiosulfate concentrations, species such as Ag2(S203) 3 are present. Silver sulfide dissolves in alkaline sulfide solutions to form complex ions such as Ag(S 2 Ag(HS) 4. These ions are... 

Quantitative. Classically, silver concentration ia solution has been determined by titration with a standard solution of thiocyanate. Ferric ion is the iadicator. The deep red ferric thiocyanate color appears only when the silver is completely titrated. GravimetricaHy, silver is determined by precipitation with chloride, sulfide, or 1,2,3-benzotriazole. Silver can be precipitated as the metal by electro deposition or chemical reduciag agents. A colored silver diethjldithiocarbamate complex, extractable by organic solvents, is used for the spectrophotometric determination of silver complexes. 

Thin films of photochromic silver complex oxides were prepared by anodic oxidation of silver metal films (15). Complex oxides, such as Ag2V04, Ag SiO, and Ag2P04, darkened by exposure to visible light, but required heating to 150—250°C for thermal bleaching. 

Release by Silver-Assisted Cleavag e. A soluble silver complex formed imagewise in the undeveloped areas of the silver haUde layer may be used to effect a cleavage reaction that releases a dye or a dye precursor. The process yields positive dye transfer images directiy with negative-working emulsions (46). An example is the silver-assisted cleavage of a dye-substituted thiazolidine compound, as shown in equation 7. 

Some KCN is used to form the silver complex the excess is called free CN . NaCN has been used, but has some deficiencies. 

Porphyrin, octaethyl-, silver complex cyclic voltammetry, 4, 399 <73JA5140)... 

The perfluoroalkylsilver complexes exist in a dynamic equilibrium in solution with solvated silver ion and anionic perfluoroalkylsilver complexes such as Ag[CF(CF5) r [277] The triflnoromethylated silver complex, Ag(CF3)4 , is prepared via reaction of bis(trifIuoromethyl)cadmium with silver nitrate in acetoni trile [278]... 

Ti in [Ti(> 2-Cl04)4] and Ni" in [Ni(>j -C104)L2] where L is a chiral bidenlate organic ligand.Sometimes both and modes occur in the same compound. The biden-latc bridging mode occurs in the silver complex [Ag /x,>j -00(0)20- (m-xylene)2]- The structure of appropriate segments of some of these compounds arc in Fig. 17.23. The distinction between coordinated and non-coordinaied ( ionic ) perchlorate is sometimes hard to make and there is an almost continuous... 

Many alkenes and arenes react directly with dissolved silver salts to afford crystals of the silver complex. Examples studied by X-ray diffraction [151] include (C6H6)AgX (X = C104, A1C14) and (C8H8)AgN03. 

This group showed that isolable silver(I) diaminocarbene complexes can be use in situ instead of free carbenes, to generate the copper carbene complex. The silver salts that precipitates during the formation of the copper complex have not any negative effect on the conversion. This method is advantageous since most of the silver complexes are isolable, air-stable and easily obtained by treatment of the corresponding imidazohnium salt by 0.5 equiv of silver oxide (Scheme 53). The solid structure of 78 was analyzed by X-ray diffraction. 

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