The coordination polymer, (Zn(II)-CP, 1),
{[Zn(2,6-NDC)(4-Cltpy)](H2O)4} (1) (2,6-H2NDC = 2,6-naphthalene
dicarboxylic acid and 4-Cltpy = 4′-chloro-[2,2′;6′,2″]terpyridine)
is structurally characterized by single crystal X-ray diffraction
measurement and other physicochemical studies (PXRD, FTIR, thermal
analysis, microanalytical data). 4-Cltpy acts as end-capping ligand,
and NDC2– is a carboxylato bridging motif to constitute
ZnN3O2 distorted trigonal bipyramid core that
propagates to construct 1D chain. The coordination polymer, 1, detects total iron (Fe3+ and Fe2+) in aqueous solution by visual color change, colorless to pink.
Absorption spectrophotometric technique in aqueous medium measures
the limit of detection (LOD) 0.11 μM (Fe2+) and 0.15
μM (Fe3+), and binding constants (Kd)
are 6.7 × 104 M–1 (Fe3+) and 3.33 × 104 M–1 (Fe2+). Biocompatibility of 1 is examined in live cells,
and intracellular Fe2+ and Fe3+ are detected
in MDA-MB 231 cells. Zn(II) substitution is assumed upon addition
of FeIII/FeII solution to the suspension of
the coordination polymer, 1, in water–acetonitrile
(41:1) (LZnII + FeIII/II → LFeIII + ZnII, where L is defined as coordinated ligands), which
is accompanied by changing from colorless to pink at room temperature.
The color of the mixture may be assumed to the charge transfer transition
from carboxylate-O to Cltpy via Fe(II/III) bridging center (carboxylate–O–Fe-CltPy).
The product isolated from the reaction is finally characterized as Fe(III)@1-CP. It is presumed that product Fe(II)@1-CP may undergo fast aerial oxidation to transform Fe(III)@1-CP. The FeIII exchanged framework (Fe(III)@1-CP) has been characterized by PXRD, IR, TGA and energy dispersive
X-ray analysis (EDX)-SEM. The MTT assay calculates the cell viability
(%), and the tolerance limit is 100 μM to total Fe2+ and Fe3+.