Silver, ligands

Discrimination between exposed and unexposed areas in this process requires the selection of thia zolidine compounds that do not readily undergo alkaline hydrolysis in the absence of silver ions. In a study of model compounds, the rates of hydrolysis of model /V-methyl thia zolidine and A/-octadecyl thiazolidine compounds were compared (47). An alkaline hydrolysis half-life of 33 min was reported for the /V-methyl compound, a half-life of 5525 min (3.8 days) was reported for the corresponding V/-octadecyl compound. Other factors affecting the kinetics include the particular silver ligand chosen and its concentration (48). Polaroid Spectra film introduced silver-assisted thiazolidine cleavage to produce the yellow dye image (49), a system subsequentiy used in 600 Plus and Polacolor Pro 100 films. 

To maintain color isolation, it is important for the exposed grains of each emulsion layer to be substantially developed before a dye developer assigned to a different emulsion layer reaches them. Both the auxiUary developer and the barrier interlayers assist in such isolation. Color isolation may also be assisted by the release of low solubiUty silver ligands, such as mercaptans (65). 

Figure 2.2 Models showing effects of presence or absence of H bonding on silver/ligand complex and dipolarphile. (Taken from ref. 53 with permission.)...

Computational studies yielded the models shown in Figure 2.2. These models illustrate how the existence or absence of hydrogen bonding between the silver/ligand complex and the dipolarphile may lead to selection of opposite faces in the reaction with the silver-bound azomethine ylide derived from 111. 

Infinite ladders, which include solvent molecules, are shifted by a rung distance against each other and stacked like a stair in the direction of the b-axis. A two-dimensional square lattice of 34 is obtained from Cd and 4,4 -bipyridine (see Experiment 7-6, Section 7.7) [102,109]. Aromatic guest molecules can be incorporated, and the polymer catalyze the cyanosilylation of aldehydes [102]. The structure of [Ag(4,4 -bipyridine)N03] consists of linear silver-ligand chains which are crosslinked by an Ag-Ag interaction [110]. Infinite channels (2.3 x 0.6 nm) are formed which can reversibly incorporate PFe, Mo04 , BF4 and S04 ions. Pyrazine has also been used as a building block [111]. 

Despite the considerable synthetic potential of this reaction, only two NHC-con-taining catalysts have been reported to date. The in situ generated complex from the reaction between [RhCl(COD)]2 and a NHC-silver ligand transfer reagent was active in the arylation of an A-phosphinoyl aldimine with phenylboronic acid, but... 

Liu, D., R.K. Meruva, R.B. Brown, and M.E. Meyerhoff. 1996. Enhancing EMF stabihty of sohd-state ion-selective sensors by incorporating hpophihc silver-ligand complexes within polymeric films. Anal. Chim. Acta ill. 173-183. 

Despite the considerable synthetic potential of this reaction, only two NHC-containing catalysts have been reported to date. The in situ generated complex from the reaction between [RhCl(COD)]2 and the NHC-silver ligand transfer reagent 20 was found to be active in the arylation of an At-phosphi-noyl aldimine with phenylboronic acid but unfortunately only one catalytic test was performed [eqn (8.9)]. In a more systematic study, Suzuki and Sato screened various azolium salts, among which the system [RhCl(COD)]2/ lAd-HCl proved to be the most active catalyst for the arylation of a series of A -sulfonyl and A -phosphinoyl arylimines. ... 

Halogens can act as ligands and are commonly found in complex ions the ability of fluorine to form stable complex ions with elements in high oxidation states has already been discussed (p. 316). However, the chlorides of silver, lead(Il) and mercury(l) are worthy of note. These chlorides are insoluble in water and used as a test for the metal, but all dissolve in concentrated hydrochloric acid when the complex chlorides are produced, i.e. [AgCl2] , [PbC ] and [Hg Clj]", in the latter case the mercury(I) chloride having also disproportionated. 

The complexes of copper(I) like those of silver(I) (p. 430), but unlike those of preceding transitions metals, tend to prefer a linear coordination of two ligands, i.e. X—Cu—X thus copper(I) chloride in aqueous ammonia gives the colourless [Cu(NH3)2] (readily oxidised in air to give blue [Cu (NH3)4(H20)2] copper(I) chloride in hydrochloric acid gives [CuClj], although [CuCl3] is also known. 

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. 

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. 

Silver(II) Compounds. Sdver(II) is stabilized by coordination with nitrogen heterocychc bases, such as pyridine and dipyridyl. These cationic complexes are prepared by the peroxysulfate oxidation of silver(I) solutions in the presence of an excess of the ligand. An extensive review of the higher oxidation states of silver has beenpubhshed (21). 

In titanium acylates, the carboxylate ligands are unidentate, not bidentate, as shown by ir studies (333,334). The ligands are generally prepared from the hahde and silver acylate (335). The ben2oate is available also from a curious oxidative addition with ben2oyl peroxide (335—338) ... 

Although trialkyl- and triarylbismuthines are much weaker donors than the corresponding phosphoms, arsenic, and antimony compounds, they have nevertheless been employed to a considerable extent as ligands in transition metal complexes. The metals coordinated to the bismuth in these complexes include chromium (72—77), cobalt (78,79), iridium (80), iron (77,81,82), manganese (83,84), molybdenum (72,75—77,85—89), nickel (75,79,90,91), niobium (92), rhodium (93,94), silver (95—97), tungsten (72,75—77,87,89), uranium (98), and vanadium (99). The coordination compounds formed from tertiary bismuthines are less stable than those formed from tertiary phosphines, arsines, or stibines. 

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... 

Pyridine bases are well known as ligands in complexes of transition metals, and it might well be anticipated that the equilibrium constants for the formation of such complexes, which are likely to be closely related to the base strength, would follow the Hammett equation. Surprisingly, only very few quantitative studies of such equilibria seem to have been reported, and these only for very short series of compounds. Thus, Murmann and Basolo have reported the formation constants, in aqueous solution at 25°, of the silver(I) complexes... 

Complexes of rf-elements with heterocyclic ligands as promising components of non-silver photographic systems 97UK735. 

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