NICKEL(II) COMPLEX OF 6,6'-BIS(HEXYLBENZOYLAMINO)-2,2'-BIPYRIDINE AS A FUNCTIONAL CARRIER - PH-INDUCED AFFINITY-SWITCHING AND MECHANISM OF THE SCN--SELECTIVE UP-HILL TRANSPORT
Sk. Lee et al., NICKEL(II) COMPLEX OF 6,6'-BIS(HEXYLBENZOYLAMINO)-2,2'-BIPYRIDINE AS A FUNCTIONAL CARRIER - PH-INDUCED AFFINITY-SWITCHING AND MECHANISM OF THE SCN--SELECTIVE UP-HILL TRANSPORT, Bulletin of the Chemical Society of Japan, 69(5), 1996, pp. 1213-1221
The Ni(II) complex of 6,6'-bis(hexylbenzoylamino)-2,2'-bipyridine (LH(
2)) in square-planar symmetry underwent a reversible and simultaneous
deprotonation of the two amide units. The non-deprotonated complex (Ni
LH(2)(2+)) showed high SCN- selectivity by the preferential axial coor
dination of two SCN- molecules (log K-SCN = 8.11 +/- 0.03 in CH2Cl2 at
20 degrees C), while the deprotonated complex showed little affinity
toward anions. Deprotonation-induced affinity-switching of the complex
by the external aqueous layer mediated an efficient SCN- -selective u
p-hill transport across a CH2Cl2 liquid membrane by coupling with the
symport of protons from pH 4.0 to 6.0 aqueous solutions. Equilibrium a
t the aqueous/organic interface could be represented by the equation K
-app = ([Ni(LH(2))(SCN)(2)](org))/( [NiL](org)[H+](2)(aq) [SCN--](2)(a
q)), where K-app is the equilibrium constant (log K-app = 13.6 at 20 d
egrees C). However, the rates of protonation and deprotonation of the
complex at the interface were dependent mostly on the concentration of
the complex in the organic layer. Based on these results, detailed me
chanisms of the transport are discussed.