Solvation Structure of a Copper(II) Ion in Protic Ionic Liquids Comprising N-Hexylethylenediamine

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• 作者：Shinobu Takemura ; Sayaka Kawakami ; Masafumi Harada ; Masayasu Iida
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：September 15, 2014
• 年：2014
• 卷：53
• 期：18
• 页码：9667-9678
• 全文大小：624K
• ISSN：1520-510X

文摘

The fine and dynamic structure of the copper(II) ion solvated in a protic ionic liquid (PIL) comprising monoprotonated N-hexylethylenediaminium (HHexen⁺) and bis(trifluoromethanesulfonyl)amide (Tf₂N^{鈥?/sup>) [or trifluoroacetate (TFA鈥?/sup>)] was determined using NMR, visible electronic, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The chelate-diamine group in the cationic unit facilitates advantageous dissolution of transition-metal salts in the present PIL. The interaction of the copper(II) ion with the chelate-diamine PIL was explored by the addition of copper(II) salts to the PIL, demonstrating competitive complexation between the ligand of the added copper(II) salt and the components of the ionic liquid to the copper(II) ion. The favorable mode of interaction of the present chelating PIL with the copper(II) ion was clarified based on a comparison of the interactions with analogous liquids, including the monoprotonated hexylaminium HHexam(Tf₂N)-PIL, neat N-hexylethylenediamine (Hexen), and neat ethylenediamine (En). The coordination modes of the bis-Hexen and tris-Hexen copper(II) complexes in molecular liquids and in solids were also studied for comparison of the coordination structures around the copper(II) ion with those in the present PILs. The paramagnetic-induced relaxations derived from 13C (螖T_1p鈥?) and 15N (螖T_2p鈥?) NMR, the visible electronic spectra, and EXAFS analysis showed that the copper(II) ion tends to form a bis-Hexen complex in the HHexen-PIL despite the electrostatic repulsion and the fact that the counteranions are located at the axial sites, whereas in the HHexam(Tf₂N)-PIL, the copper(II) ion exhibits affinity for the Tf₂N anion over the protonated amines. The lifetime of the copper(II) complex formed in the PIL was determined to be 鈮?0鈥? s based on 13C (螖T_1p鈥?) and 14N (螖T_2p鈥?) NMR, which is appreciably longer than that in conventional molecular solvents.}