An integrated experimental and theoretical investigation of the vibrational modes and molecular structure of a chelate, tetraaqua cysteine aluminum(III)

•Al3+:cysteine system M:L ratios 1:1 and 1:5 were studied in aqueous solution.•Potentiometry, Raman spectroscopy and DFT calculations were used.•Cysteine acts as a bidentate ligand in tetraaaqua cysteine aluminum(III).•The geometric arrangement adopted was distorted octahedral.

The complex formed by Al3+ and cysteine in aqueous solution has been studied by potentiometry, Raman spectroscopy and DFT calculations (DFT:B3LYP/6-311++G∗∗).Atomic charges, frontier molecular orbitals, electrostatic potential contour surface, electrostatic potential map and donor–acceptor second order perturbative energies were examined. The [Al(Cys)(H2O)4]2+ complex adopts a distorted octahedral geometry. Cysteine should act as a bidentate ligand through the oxygen of the carboxylate and the nitrogen of the amino group. The molecule has high HOMO–LUMO energy gap, intense intramolecular charge transfer and positive electrostatic potential.

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