Although a large number of nitrogen-heterocyclic hydrazones have been
used as chromogenic reagents in the spectrophotometric determination o
f divalent transition metal ions, there is only a little information o
n the complexation behavior of these hydrazones in terms of thermodyna
mics and kinetics. In order to increase sensitivity or solubility, bul
ky substituents such as pyridyl and quinolyl groups are often introduc
ed into extractive-spectrophotometric reagents. However, application o
f linear free energy relationship (LFER) to formation of metal-multide
ntate ligand complexes has been scarcely discussed. In this study, the
extractive-spectrophotometric determination of trace metal ions and a
nions with hydrazones were established. The extraction behavior was in
terpreted in terms of complexation parameters in aqueous or aqueous-di
oxane solution and LFER. The extraction mechanisms were confirmed by e
quilibrium and kinetic experiments. First, the acid-base equilibria we
re discussed in connection with the ligand structures with the aid of
several spectrometric (NMR, X-ray etc.) results. Second, the formation
constants of the Ni(II), Cu(II) and Fe(II) complexes with a series of
hydrazones were determined. The LFER between formation and proton dis
sociation constants showed several structural effects, in addition to
the effect of basicity, which were caused by the N,N,N-heterocyclic st
ructure. The LFER obtained were discussed in connection with thermodyn
amic and ligand field parameters and were reasonably explained by the
additivity of the structural effects on the formation constants. Third
ly, the extraction equilibria of nickel(II) were elucidated based on t
he results of the second study. The extraction kinetics was discussed
in conjunction with the rate constants of formation of nickel(II)-hydr
azone complexes. Finally, a method for the determination of trace elem
ents with hydrazones having a di-2-pyridyl ketone moiety was proposed
and some favourable effects of the ketone moiety were discussed.