A review on the complex forming ability of O-O′ type ligands with transition metals: introducing 2,3-dihydroxynaphthalene as a potential analytical reagent

Abstract

O-O′ type organic compounds and their derivatives are known to form a host of complexes in solutions, and many of them have been isolated in solid forms and characterized by physicochemical techniques, including X-ray crystallography. Some of the complexes have been shown to have biological significance. Many of the complexes of ortho-dihydroxybenzene and -naphthalene formed in solution with metal ions, particularly transition metals, display distinct colors under different reaction conditions. These colored complexes are often suitable for spectrophotometric determinations of the metals. Comparative studies carried out on a host of complexes of metal ions with different ortho-dihydroxybenzenes and -naphthalenes reveal that the color complexes formed of the latter are invariably more sensitive than those formed of the former because of ring size and extended conjugations. Among the ortho-dihydroxynaphthalenes studied, the one having oxygen atoms at positions 2 and 3 of the ring [2,3-dihydroxynaphthalene (2,3-H₂ND)] has high propensity to form colored complexes with a host of metal ions suitable for liquid-liquid extraction under different reaction conditions. A survey of the literature reveals that except for a few scarce reports, the analytical potential of this ligand, although it had in the past been extensively used in the synthesis and structural assessment of numerous complexes with different metal ions, has not been explored thoroughly until recently studied in detail in the authors’ laboratory. This paper presents a non-exhaustive review on the complex forming ability of 2,3-H₂ND vis-à-vis those of its other counterparts, with special reference to its analytical applications.