Complexation of Lanthanides with Glutaroimide-dioxime: Binding Strength and Coordination Modes

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• 作者：Seraj A. Ansari ; Yanqiu Yang ; Zhicheng Zhang ; Kevin J. Gagnon ; Simon J. Teat ; Shunzhong Luo ; Linfeng Rao
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：February 1, 2016
• 年：2016
• 卷：55
• 期：3
• 页码：1315-1323
• 全文大小：584K
• ISSN：1520-510X

文摘

The complexation of lanthanides (Nd³⁺ and Eu³⁺) with glutaroimide-dioxime (H₂L), a cyclic imide dioxime ligand that has been found to form stable complexes with actinides (UO₂²⁺ and NpO₂⁺) and transition metal ions (Fe³⁺, Cu²⁺, etc.), was studied by potentiometry, absorption spectrophotometry, luminescence spectroscopy, and microcalorimetry. Lanthanides form three successive complexes, M(HL)²⁺, M(HL)L, and M(HL)₂⁺ (where M stands for Nd³⁺/Eu³⁺ and HL^– stands for the singly deprotonated ligand). The enthalpies of complexation, determined by microcalorimetry, show that the formation of these complexes is exothermic. The stability constants of Ln³⁺/H₂L complexes are several orders of magnitude lower than that of the corresponding Fe³⁺/H₂L complexes but are comparable with that of UO₂²⁺/H₂L complexes. A structure of Eu³⁺/H₂L complex, identified by single-crystal X-ray diffractometry, shows that the ligand coordinates to Eu³⁺ in a tridentate mode, via the two oxygen atoms of the oxime group and the nitrogen atom of the imide group. The relocation of protons of the oxime groups (?CH═N–OH) from the oxygen to the nitrogen atom, and the deprotonation of the imide group (?CH–NH–CH?) result in a conjugated system with delocalized electron density on the ligand (?O–N–C–N–C–N–O?) that forms strong complexes with the lanthanide ions.