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

Abstract Combination of pyridine, antipyrine and indole in a single molecule ( L2 ) allows selective recognition of Fe 3 + colorimetrically in CH 3 CN. The structure of L2 is confirmed from single crystal X-ray diffraction analysis. The probe displays two different visible bands at 541 nm and 715 nm in the presence of Fe 3 + , associated with two different colors, viz. green and pink-violet allowing determination of unknown Fe 3 + concentration. Interestingly, removal of 2-picolyl group from indole N-center of L2 generates L3 that behaves similarly at low Fe 3 + concentration (> 0 to 1.1 mM) but differently at higher Fe 3 + concentration (> 1.1 mM), indicating involvement of pyridyl-N donor towards Fe 3 + , and hence different coordination environment around Fe 3 + at higher concentration.