COMPLEXATION BEHAVIOR OF HETEROCYCLIC HYDRAZONES .2. EFFECTS OF STERIC FACTORS ON FORMATION-CONSTANTS FOR NICKEL(II) COMPLEXES WITH HETEROCYCLIC HYDRAZONES
T. Taya et al., COMPLEXATION BEHAVIOR OF HETEROCYCLIC HYDRAZONES .2. EFFECTS OF STERIC FACTORS ON FORMATION-CONSTANTS FOR NICKEL(II) COMPLEXES WITH HETEROCYCLIC HYDRAZONES, Bulletin of the Chemical Society of Japan, 67(3), 1994, pp. 710-719
The equilibria of nickel(II) ion with thirteen nitrogen-heterocyclic h
ydrazones (neutral form: HL) with and without blocking group(s) have b
een investigated spectrophotometrically in 28% aqueous dioxane solutio
n at 25-degrees-C and an ionic strength of 0.2 (KCl). For a series of
2-pyridinecarbaldehyde 5-substituted-2-pyridylhydrazones, the followin
g linear free energy relationships (LFER) were derived between the ove
rall formation constants, beta1, beta1', and beta2, of Ni(HL)2+, NiL+,
and Ni(HL)22+ complexes, respectively, and the dissociation constants
, K(a1) and K(a2), of H3L2+ and H2L+, respectively: log beta1 = 0.95 (
pK(a1) + pK(a2))/2 + 4.60, 1/2 log beta2 = 0.95 x (PK(a1) + PK(a2))/2
+ 4.82, and log beta1' = 1.40 (pK(a1) + PK(a2))/2 + 9.73. The steric e
ffects of the 6-methyl group in pyridine and the quinolyl ring in plac
e of pyridyl group on the complex formation were evaluated on the basi
s of LFER. The complex stabilization effect of the pyridyl group subst
ituted for formyl hydrogen was also evaluated for Ni(HL)22+, Ni(HL)2+,
and NiL+ complexes. These results together with LFER were discussed i
n conjunction with the thermodynamic parameters for the formation of N
i(HL)2+ complex and the ligand field parameters, D(q), for Ni(HL)2+ an
d Ni(HL)22+ complexes.