Structure and coordination modes in the interaction between Cd2+ and 3-mercaptopropionic acid

The structural, electronic, and energetic properties of cadmium ion complexes with one and two protonated and deprotonated 3-mercaptopropionic acid ligands were studied theoretically in the framework of density functional theory by using the B3LYP exchange-correlation functional coupled with 6-311++G** Gaussian orbital basis sets for C, H, O, and S atoms and LANL2DZ for the metal ion. The study was extended to the aqueous complexes introducing explicitly some water molecules in order to simulate the tetrahedral and octahedral coordination sphere of the Cd2+ ion. Results indicate that the complexes containing only one ligand have a cyclic structure in which the metal ion binds both oxygen and sulfur atoms. The tetrahedral topology is preferred in the complexes with two ligands.