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Sm(iii) Complexation with amino acids. Crystal structures of [Sm2(Pro)6(H2O)6](ClO4)6 and [Sm(Asp)(H2O)4]Cl2
Abstract
Samarium complexes with amino acids have been studied by potentiometric measurements. Experiments were performed in aqueous solution at 37.0 °C and 0.15 M NaClO4, resembling physiological medium. Low stability Sm(III)–amino acid complexes were detected. Complexes with 1 ∶ 1 ligand to metal molar ratios are predominant in the studied pH interval. Other mono- and di-nuclear species can be detected up to pH 6. For higher pH values, hydrolysis to [Sm(OH)]2+ and Sm(OH)3 becomes the main process. Some of the studied complexes were isolated and characterized in the solid state. Single-crystal X-ray structures of [Sm2(Pro)6(H2O)6](ClO4)6 (1) and [Sm(Asp)(H2O)4]Cl2 (2) are reported. In both complexes, an eight coordinate Sm atom is found, surrounded by carboxylate groups and water molecules. In 1, Sm atoms form infinite chains bridged by proline ligands (via carboxylate groups). An additional monodentate amino acid is present in the coordination sphere of each Sm center. In 2, the amino acid also bridges Sm atoms but using α and β carboxylate groups. The overall structure consists of infinite planes in which all carboxylate groups, acting as bidentate ligands, are bonded to Sm atoms.
6 and [Sm(Asp)(H2O)4]Cl2](/en/Image/Get?imageInfo.ImageType=GA&imageInfo.ImageIdentifier.ManuscriptID=B204095F&imageInfo.ImageIdentifier.Year=2002)
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