Tuning the Selectivity of Gd3N Cluster Endohedral Metallofullerene Reactions with Lewis Acids

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• 作者：Steven Stevenson ; Khristina A Rottinger ; Muska Fahim ; Jessica S Field ; Benjamin R Martin ; Kristine D Arvola
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：December 15, 2014
• 年：2014
• 卷：53
• 期：24
• 页码：12939-12946
• 全文大小：488K
• ISSN：1520-510X

文摘

We demonstrate the manipulation of the Lewis acid strength to selectively fractionate different types of Gd₃N metallofullerenes that are present in complex mixtures. Carbon disulfide is used for all Lewis acid studies. CaCl₂ exhibits the lowest reactivity but the highest selectivity by precipitating only those gadolinium metallofullerenes with the lowest first oxidation potentials. ZnCl₂ selectively complexes Gd₃N@C₈₈ during the first 4 h of reaction. Reaction with ZnCl₂ for an additional 7 days permits a selective precipitation of Gd₃N@C₈₄ as the dominant endohedral isolated. A third fraction is the filtrate, which possesses Gd₃N@C₈₆ and Gd₃N@C₈₀ as the two dominant metallofullerenes. The order of increasing reactivity and decreasing selectivity (left to right) is as follows: CaCl₂ < ZnCl₂ < NiCl₂ < MgCl₂ < MnCl₂ < CuCl₂ < WCl₄ 鈮?WCl₆ < ZrCl₄ < AlCl₃ < FeCl₃. As a group, CaCl₂, ZnCl₂, and NiCl₂ are the weakest Lewis acids and have the highest selectivity because of their very low precipitation onsets, which are below +0.19 V (i.e., endohedrals with first oxidation potentials below +0.19 V are precipitated). For CaCl₂, the precipitation threshold is estimated at a remarkably low value of +0.06 V. Because most endohedrals possess first oxidation potentials significantly higher than +0.06 V, CaCl₂ is especially useful in its ability to precipitate only a select group of gadolinium metallofullerenes. The Lewis acids of intermediate reactivity (i.e., precipitation onsets estimated between +0.19 and +0.4 V) are MgCl₂, MnCl₂, CuCl₂, and WCl₄. The strongest Lewis acids (WCl₆, ZrCl₄, AlCl₃, and FeCl₃) are the least selective and tend to precipitate the entire family of gadolinium metallofullerenes. Tuning the Lewis acid for a specific type of endohedral should be useful in a nonchromatographic purification method. The ability to control which metallofullerenes are permitted to precipitate and which endohedrals would remain in solution is a key outcome of this work.