Lanthanide Triple-Stranded Helicates: Controlling the Yield of the Heterobimetallic Species

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• 作者：Thomas B. Jensen ; Rosario Scopelliti ; Jean-Claude G. B&uuml ; nzli
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：September 18, 2006
• 年：2006
• 卷：45
• 期：19
• 页码：7806 - 7814
• 全文大小：270K
• 年卷期：v.45,no.19(September 18, 2006)
• ISSN：1520-510X

文摘

Two unsymmetrical ditopic hexadentate ligands designed for the simultaneous recognition of two different trivalentlanthanide ions have been synthesized, L^AB2 and L^AB3, where A represents a tridentate benzimidazole-pyridine-benzimidazole coordination unit, B2 a diethylamine-substituted benzimidazole-pyridine-carboxamide one, and B3 achlorine-substituted benzimidazole-pyridine-carboxamide moiety. Under stoichiometric 2:3 (Ln/L) conditions, theseligands self-assemble with lanthanide ions to yield triple-stranded bimetallic helicates. The crystal structures of fourhelicates with L^AB3 of composition [LnLn'(L^AB3)₃](ClO₄)₆·solv (CeCe, PrPr, PrLu, NdLu) show the metal ions embeddedinto a helical structure with a pitch of about 13.2-13.4 Å. The metal ions lie at a distance of 9.1-9.2 Å and arenine-coordinated by the three ligand strands, which are oriented in a HHH (head-head-head) fashion, where allligand strands are oriented in the same direction. In the presence of a pair of different lanthanide ions in acetonitrilesolution, the ligand L^AB3 shows selectivity and gives high yields of heterobimetallic complexes. L^AB2 displays lessselectivity, and this is shown to be directly related to the tendency of this ligand to form high yields of HHT(head-head-tail) isomer. A fine-tuning of the HHH ges/entities/lrarr2.gif"> HHT equilibrium and of the selectivity for heteropairs of Ln^IIIions is therefore at hand.