Single crystal X-ray-structurally characterized Mo(vi) complexes of thiophene-appended amide–imine conjugates for optical recognition of calcon and 2-aminobutyric acid

Abstract

Two thiophene-appended amide–imine conjugates, viz., thiophene-2-carboxylic acid (3,5-ditertiarybutyl-2-hydroxybenzylidine)hydrazide (L1) and thiophene-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidine)hydrazide (L2), have been prepared by the condensation of thiophene-2-carboxylic acid hydrazide (TCA) with the respective aldehydes. L1 and L2 have further been employed for the synthesis of the corresponding Mo(VI) complexes (M1 and M2, respectively). The structures of M1 and M2 have been confirmed by single-crystal X-ray diffraction analysis. Fluorescence spectroscopic studies indicate that M1 and M2 efficiently and selectively recognize calcon and 2-aminobutyric acid, respectively. The proposed sensing mechanism involves the displacement of the ligands from M1 and M2 by the respective analytes. The displacement binding constants are 6.2 × 10³ M⁻¹ (for calcon) and 12.9 × 10⁴ M⁻¹ (for 2-aminobutyric acid). The detection limits for calcon and 2-aminobutyric acid are 6 nM and 5 nM, respectively, in DMSO/H₂O (4/1, v/v, pH 7.4).