A highly sensitive and selective fluorescent sensor for Al3+ ions based on thiophene-2-carboxylic acid hydrazide Schiff base

An efficient fluorescent receptor (E)-N-[(2-hydroxy-naphthalen-1-yl)methylene]thiophene-2-carbohydrazide (THN) for Al3+ ions was synthesized and characterized by physicochemical and spectroscopic tools along with single crystal X-ray crystallography. This is the first report showing the crystal structure of THN and its sensing property for Al3+ ions. THN selectively and sensitively detects Al3+ ions without any interference among various cations, Na+, K+, Ca2+, Cr3+, Mg2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+ and Hg2+ by a strong fluorescent change in ethanol-water medium (EtOH-H2O, 1 : 4 v/v). The THN interacts with Al3+ in a tridentate mode to form a [AlCl2(THN)(H2O)]center dot H2O complex. The binding constant was determined to be 7.06 x 10(6) M-1 and the limit of detection (LOD) was calculated to be 1.35 x 10(-9) M which is the second highest reported till date in the literature. The H-1 NMR titration, ESI-MS and DFT studies have also been performed in support of the binding details of the THN-Al3+ complex.