Silver cryptate

Tab. 4.3 Standard potentials of. silver cryptates-silver electrodes (AgL+/Ag) [4] 1) ...

Table 4.3 shows the standard potentials of the Ag+/Ag and AgL+/Ag electrodes in various aprotic solvents, where L stands for cryptands [4]. The standard potential of the Ag+/Ag electrode varies with solvent by more than 500 mV. However, the standard potentials of the AgL+/Ag electrodes are not much influenced by solvent, the variations being 80 mV at most. For silver cryptates, AgL+, the relation logy, (Agl., R-> S) logyt(L, R-> S) holds, as described in Section 2.4. From this and p=1 in Eq. (4.7), the relation °(R) °(S) can be expected. 

The Ag/Ag" " electrode is reversible [200] in many solvents. The main advantage of this and similar reference electrodes is that it allows working in a system containing a single solvent. Silver ions react with certain organic solvents, such as DMF, and other metal electrodes must then be used however, a silver cryptate electrode [Ag/0.005 M Ag Cryp(2.2)004] is stable in DMF [201]. 

As supporting electrolyte, tetraalkylammonium perchlorates or fluoroborates are mostly used, but LiCl or NaC104 may also be employed. The reference electrode may be a modified Ag/AgCl electrode [211,216], a Cd(Hg)/Cd" electrode [211,216], Na(Hg)/ Na" electrode [205], or silver/silver cryptate electrode [201]. 

Bessiere, J. Lejaille, M. (1979) Utilisation of Silver Cryptate [222] /Silver System as a Potential Reference for the Etetermination of the Solvation Transfer Coefficients of Ions. Stability of Cryptates in a Solvent Medium, Anal. Lett, 12 753 - 763. 

Similarly, by Schiff-base condensation reactions have been used to generate free cryptands from triamines and dicarbonyls in [2+3] condensation mode. These ligands react with silver(I) compounds to give dinuclear or trinuclear macrocyclic compounds where Ag Ag interactions may be present. Thus, with a small azacryptand a dinuclear complex with a short Ag- Ag distance (55) is found.498 With bigger azacryptand ligands also dinuclear complexes as (56) are achieved but without silver-silver interaction. 65,499-501 A heterobinuclear Ag1—Cu1 cryptate has also been... 

Results with Sr ] in Mice. While the results with Ag cryp-tate were encouraging, we sought further preliminary evidence of the potential value of labeled cryptates as blood-flow radiopharmaceuticals. There were several reasons for these studies the monovalent silver ion is very polarizable and thus may not be a general model for monovalent cations (5,17). In contrast, divalent cations form stronger inclusive cryptates than monovalent cations of the same ionic radii. On the other hand, the added charge of the divalent ion would require that the cryptand shield more charge if it is to result in an equally lipophilic complex. 

Table 62 Stability Constants (Log K) for Silver (2]Cryptates in Various Solvents at 25 °C...

Table 63 Thermodynamic Data for the Formation of Silver [2]Cryptates in Water at 25 °C476...

A mixed-valence silver(I)-silver(III) cryptate complex has been synthesized by condensation of tris(3-aminopropyl)amme and terephthaldehyde in the presence of AgNOs. Other pyridine silver(III) complexes have been obtained by oxidation of silver nitrate and ammonia with ammonimn peroxydisulfate in aqueous ammonia solution. An air-stable diamagnetic silver(III) complex of a N-confused tetraphenylporphyrin, 5,10,15,20-tetraphenyl-2-aza-21-carboporphyrin argentate(III), has been described. ... 

ESTERS Cryptates. Dihalobis(triphenylphosphine)palladium(ll). Ion-exchange resins. Peracetic acid. Silver tetrafluoroborate. Thallous 2-methylpropane-2-thiolate. 2,4,6-Tri methyIbenzenesulfonyl chloride. 

A further step in complexity was aecomplished by designing ligands able to eomplex more than one cation eryptand 8 (Fig. 8), for example, forms a homodinuclear complex with silver or copper.The erystal stracture of the dinuclear Cu(I) eomplex formed with the hexaimine macrobicycle 8 shows the inelusion of the two copper ions, which are tetracoordinated at each end of the cavity, the Cu...Cu distance being very large (11.07 A). The small hexaimine macrobicycle 9 (Fig. 9) forms a Cu(l) dinuclear complex in which the Cu(I)... Cu(l) distance is short (2.45 A). In the reduced hgand 10 (Fig. 10), the Cu(I) is not stable, and only the [Cu2 (lO)] " cryptate was obtained. The Cu... Cu distance in this complex is 2.42 A, and on the basis of ESW measurements, an average redox state (di Cu ) was postulated rather than a Cu(I)... Cu(II) dinuclear complex. ... 

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