Colorimetric metal ion (II) Sensors Based on imine boronic esters functionalized with pyridine

The one-step synthesis of three imine boronic esters functionalized with pyridyl groups is described (1a-1c). presence or absence a methyl group affects the whole conformation, being bent “L” linear as determined by X-ray crystal diffraction. C–H⋯O, C–H⋯N, C–H⋯F and C–H … π hydrogen bond interactions support 2D supramolecular arrangements. Ligands were tested metal ion (M2+) sensors in solution. addition cations (Fe2+, Co2+ Cu2+) to 1a using methanol solvent, showed significant color changes (purple, orange green, respectively), while for Ni2+, Zn2+, Cd2+ no observed. sensitivity compound towards Fe2+, Cu2+ was monitored UV–Vis spectroscopy, where Fe2+ produces new bands at 360 566 nm. For remarkable intensity increase observed 290 nm band appear 340 462 nm, respectively. stoichiometry complexes 1a-Fe2+, 1a-Co2+ 1a-Cu2+ Job's plots 1:3 (metal:ligand, complex [Fe (1a)3]2+), contrast 1:1 1b-Fe2+. In fact, computed ΔG formation associated value strong stabilization (1a)3]2+ (−65.5 kcal/mol) comparison possible (1b)3]2+ (−29.7 kcal/mol). Detection limits are mM range (determined UV–Vis) μM Fluorescence). An analogous bis-bidentate derivative (2a) also shows similar behavior but stoichiometric interaction 2:3 (metal:ligand) detection obtained Fluorescence techniques.