Spectrophotometric Sensing of Zn(II) by Three Aryl Acid Hydrazones of Di‐2‐pyridylketone. The Influence of the Nitrogen in/on the Aryl Ring of the Acid Hydrazide

ABSTRACT The selectivity and sensitivity of di‐2‐pyridylketone benzoyl hydrazone ( dpkbh ), di‐2‐pyridylketone isonicotine hydrazone ( dpkinah ) and di‐2‐pyridylketone 4‐aminobenzoyl hydrazone ( dpk4abh ) toward Zn(II) in H 2 O‐EtOH (1:1 v/v), were determined using UV–visible spectroscopy. The binding constants (log K = β) were determined to be 6.18 ± 0.21, 6.22 ± 0.31, and 6.17 ± 0.57 with corresponding detection limits of 0.30, 0.44, and 0.58 ppm, for dpkbh , dpkinah , and dpk4abh , respectively. The sensitivity towards Zn(II) (Δabs/Δ[Zn]) were 19400, 16350, and 14690 M −1 for dpkbh , dpkinah , and dpk4abh , respectively. Zn(II) can be selectively quantified in the presence of Pb(II) via the addition of of HPO 4 2– (in the form Na 2 HPO 4 •7H 2 O) without affecting the detection limit of Zn(II). Overall, the results suggested that the substitution of a ring carbon with nitrogen or with an amine group (at the para ‐positions) had no distinguishable influence on the binding constant of the ligand toward Zn(II), and slightly reduced the detection limit of the dpk‐benzoyl like hydrazones. DFT studies suggested that the Zn‐dpkbh interaction had the greatest covalent character, which translated to the greatest sensitivity toward Zn(II).