Synthesis, solution studies and DFT investigation of a tripodal ligand with 3-hydroxypyran-4-one scaffold

Hydroxypyranones form very stable complexes and possess varied uses in medical applications. They are promising chelators for treating iron overload diseases as they form stable complexes with Fe³⁺. A novel tripodal ligand tris[(5-hydroxy-4-oxo-pyran-2-yl)methyl] benzene-1,3,5-tricarboxylate (TBHPY) was synthesized and characterized by several spectroscopic techniques like UV–Vis, FT-IR, ¹HNMR, ¹³CNMR and mass spectrometry. The coordination behavior of the ligand TBHPY was investigated with proton and trivalent metal ions viz., Fe(III), Al(III) and Cr(III) by potentiometric and spectrophotometric methods. The studies revealed four species viz., L³⁻, LH²⁻_, LH₂⁻ and LH₃ for the ligand while ML, MLH and MLH₂ species for all the three metal ion complexes. In addition, only aluminium formed MLH₋₁, MLH₋₂ and MLH₋₃. Quantum mechanical studies at DFT level validated the geometrical, spectroscopic, electronic and photophysical properties of the neutral and deprotonated states of the ligand, and its metal complexes. The ligand showed a scorpio-type geometry with the presence of face-to-face stacking and hydrogen bond, whereas the neutral metal–ligand complexes displayed a distorted octahedral structure.