Synthesis, Ion Recognition Ability, and Metal-Assisted Aggregation Behavior of Dinuclear Metallohosts Having a Bis(Saloph) Macrocyclic Ligand

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• 作者：Shigehisa Akine ; Fumihiko Utsuno ; Shunjin Piao ; Hideo Orita ; Seiji Tsuzuki ; Tatsuya Nabeshima
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：January 19, 2016
• 年：2016
• 卷：55
• 期：2
• 页码：810-821
• 全文大小：714K
• ISSN：1520-510X

文摘

Macrocyclic molecule 1 that has two saloph coordination sites was designed and synthesized. The macrocycle 1 was easily converted into the corresponding metallohosts 2 and 3 by the reaction with nickel(II) and palladium(II), respectively. As expected from the molecular structure of these metallohosts having an 18-crown-6-like cavity, the nickel(II) metallohost 2 showed excellent binding affinity toward Na⁺, Ca²⁺, and Sr²⁺ to give 1:1 host–guest complexes. Preorganization effect due to the extremely rigid metal-containing macrocycle was suggested to be a major factor for the strong binding. Larger cations such as K⁺, Rb⁺, Cs⁺, and Ba²⁺ gave higher aggregated host–guest complexes such as 2₂M, 2₃M₂, and 2₄M₃. Density functional theory calculations revealed that smaller metal ions do not occupy the center of each macrocycle in the sandwich structures 2₂M, while larger Cs⁺ simultaneously interacts with all the 12 oxygen donor atoms. On the basis of the interaction energy calculations, the preference for 2·Na over 2₂Na can be explained by destabilization of 2₂Na due to the elongated Na–O bonds and repulsive three-body interactions. When the ionic radius of the guest ion increases (K⁺, Rb⁺, Cs⁺), this destabilization becomes less significant and the formation of sandwich complexes 2₂M is favored. Such aggregation would significantly affect the physical and chemical properties of the metal complexes due to the interplane interactions between the metal centers.