EPR/ENDOR and Computational Study of Outer Sphere Interactions in Copper Complexes of Phenolic Oximes

详细信息    查看全文

• 作者：Mary R. Healy ; Emma Carter ; Ian A. Fallis ; Ross S. Forgan ; Ross J. Gordon ; Eduardo Kamenetzky ; Jason B. Love ; Carole A. Morrison ; Damien M. Murphy ; Peter A. Tasker
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：September 8, 2015
• 年：2015
• 卷：54
• 期：17
• 页码：8465-8473
• 全文大小：534K
• ISSN：1520-510X

文摘

Copper complexes of the phenolic oxime family of ligands (3-X-salicylaldoximes) are used extensively as metal solvent extractants. Incorporation of electronegative substituents in the 3-position, ortho to the phenol group, can be used to buttress the interligand H-bonding, leading to an enhancement in extractant strength. However, investigation of the relevant H-bonding in these complexes can be exceedingly difficult. Here, we have combined EPR, ENDOR, DFT, and X-ray crystallography to study this effect. Analysis of the ¹H ENDOR data revealed a variation in the Cu路路路H¹⁶ (oxime proton) distance from 2.92 脜 for the unsubstituted complex [Cu(L²)₂] to 3.65 脜 for the X = CH₂N(C₆H₁₃)₂ substituted complex [Cu(L³)₂]. DFT calculations showed that this variation is caused by changes to the length and strength of the H-bond between the oximic hydrogen and the phenolate oxygen. Noticeable changes to the Cu路路路H¹⁵ (azomethine proton) distances and the Cu路路路N bonding parameters were also observed in the two complexes, as revealed through the ^NA and ^NQ ENDOR data. Distortions in the structure of the complex and variations in the oximic proton to phenolate oxygen H-bond strength caused by the substituent (X) were confirmed by DFT and X-ray crystallography. DFT directly evidenced the importance of the interaction between H¹⁶ and the amine nitrogen of CH₂N(C₆H₁₃)₂ in the buttressed complex and indicated that the high strength of this interaction may not necessarily lead to an enhancement of copper extraction, as it can impose an unfavorable geometry in the inner coordination sphere of the complex. Therefore, ENDOR, DFT, and X-ray structural data all indicate that the aminomethyl substituent (X) ortho to the phenolic oxygen atom provides a particularly strong buttressing of interligand H-bonding in these copper complexes and that these outer sphere interactions can significantly influence structure and stability.