Pyridylazo-ligands

Pyridylazo-ligands (Scheme 2) have widely been used in colorimetric analyses of various metal ions. For example, l-(2-pyridylazo)-2-naphthol (Hpan) is one of the most well-known reagents for the colorimetric determination and complexometric titration of... 

Pyridylazo ligands have been widely used in the extraction photometry of various metal ions. For example, l-(2-pyridylazo)-2-naphthol (Hpan) is one of the most well-known reagents, but it shows slow extraction rate for some metal ions such as Ni(II) and Pd(II). 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is a relatively new reagent, which is more sensitive than Hpan for Cu(II), Ni(II), Co(II), and Zn(II), giving the metal complexes of molar absorptivities in the order of 105M-1 cm-1. 

Simon et al. [47] developed a photometric flow-through sensor for the determination of zinc using a transparent PVC membrane accommodating a lipophilized ligand, viz. l-octadecyloxy-4-(2-pyridylazo)resorcinol, a water-insoluble derivative of PAR. The mechanism by which the analyte is retained in the membrane and eluted from it is similar to a liquid-liquid extraction... 

A typical kinetic synergism has been observed for the catalytic effect of iV,iV-dimethyl-4-(2-pyridylazo)aniline (PADA) on the extraction of Ni(pan)2 [72], The extraction rate of Ni(pan)2 into toluene is very slow even under an HSS condition. Whereas, the addition of PADA at the diluted concentration as 10-5M can accelerate the extraction rate about 10 times. The observed extracted species was only Ni(pan)2 and no net consumption of PADA was observed after the extraction, while a significant interfacial adsorption of PADA was observed during the extraction under the HSS condition as shown in Fig. 19. These results were analyzed by the mechanism of the interfacial ligand-substitution reaction ... 

The effect of metal chelation on the acidity of 4-(2-pyridylazo)-resorcinol (IX) has also been investigated by Freiser 18y 19), The acid dissociation constants for the ligand were found to be pKa = 7.0, pKa = 12.4. Upon coordination to a metal ion, the proton on the 3-hydroxy group is displaced so that chelation may occur. The remaining 1-hydroxy group is acidic, and the acid dissociation constants for complexes of some divalent metal ions are shown in Table IV. 

The tridentate monobasic ligand l-(2-pyridylazo)-2-naphtholate (pan) has been used to prepare seven-coordinate complexes R2(pan)M(L) (L = ACAC derivative, M = Sn, R = Bu, Me M = Pb, R = Me). For both metals the difference in 8 is distinct from lower coordination numbers, both showing an upfield shift in b of ca. 200" typical for such a change in coordination number." The dianionic tetracyclic ligand (168) is prepared from the lithiation of 2-Me-benzoxazole and reacts with tin(II) chloride to form (169)." ... 

Complex formation between Zr and HP and the ligands l-(2-pyridylazo)resorcinol (L ) and l-(2-pyridylazo-2-naphthol) (L ) has been studied polarographically. At pH 1—3 mixed hydroxo-complexes of the type M(OH)3HL and M(OH)3L are formed their stability constants have been calculated, as have those of some Zr -ethanolamine complexes. ... 

Kinetic and mechanistic studies of the reaction between 4-(2-pyridylazo)resorcinol (PAR) and (among others) NiOH and NiF were performed at an ionic strength of 0.10 M (NaC104) and at (298.15 + 0.20) K. Nickel(II) perchlorate solutions were mixed with ligand solution, then borate buffer solution (8 x 10 M) was added to adjust the pH (7 -... 

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