Influence of the solvent on the nature of the extracting species Investigation of nickel-phenanthroline/bipyridyl-rose bengal system

Nitrobenzene is found to extract nickel in the presence of 1,10-phenanthroline and Rose Bengal as an ion-association complex [Ni(Phen)(2+)(3):2RB(-)] and not as the complex [Ni(Phen)(2+)(2):2RB(-)] reported earlier as extracted into chloroform. The molar absorptivity of the nitrobenzene extract is markedly higher than that of the chloroform extract. The difference in the composition of the extracted species is very interesting. A general scheme is proposed to explain this difference on the basis of the donicity and dielectric constant of the solvent. Beer's law is obeyed in the range 0.05-1.05 ppm of Ni. Interferences of some cations and anions have been studied. Similar observations apply when 2,2'-bipyridyl is used in place of 1,10-phenanthroline.