Pyridine-antipyrine appended indole derivative for selective recognition of Fe3+: Concentration dependent coloration.

Combination of pyridine, antipyrine and indole in a single molecule (L2) allows selective recognition of Fe3+ colorimetrically in CH3CN. The structure of L2 is confirmed from single crystal X-ray diffraction analysis. The probe displays two different visible bands at 541nm and 715nm in the presence of Fe3+, associated with two different colors, viz. green and pink-violet allowing determination of unknown Fe3+ concentration. Interestingly, removal of 2-picolyl group from indole N-center of L2 generates L3 that behaves similarly at low Fe3+ concentration (>0 to 1.1mM) but differently at higher Fe3+ concentration (>1.1mM), indicating involvement of pyridyl-N donor towards Fe3+, and hence different coordination environment around Fe3+ at higher concentration.