{"title":"1H, 13C, 15N NMR, and DFT Studies on Complex Formation of Zinc(II) Ion with Ethylenediamine in Ionic Liquid [C2mIm][TFSA]","authors":"Mikio Maseda, Toshiyuki Takamuku","doi":"10.1021/acs.jpcb.4c02590","DOIUrl":null,"url":null,"abstract":"In bis(trifluoromethylsulfonyl)amide (TFSA<sup>–</sup>)-based ionic liquid (IL), 1-ethyl-3-methylimidazolium TFSA<sup>–</sup> ([C<sub>2</sub>mIm][TFSA]), the complex formation equilibria of zinc(II) ion (Zn<sup>2+</sup>) with ethylenediamine (EN) have been investigated. An EN molecule may coordinate with Zn<sup>2+</sup> as a bidentate ligand. First, the formation of Zn<sup>2+</sup>–EN complexes in [C<sub>2</sub>mIm][TFSA] was confirmed from the difference of <sup>1</sup>H and <sup>13</sup>C NMR chemical shift values of EN molecules between [C<sub>2</sub>mIm][TFSA]–EN binary solvents and the 0.1 mol dm<sup>–3</sup> Zn(TFSA)<sub>2</sub>/[C<sub>2</sub>mIm][TFSA]–EN solutions as a function of EN mole fraction <i>x</i><sub>EN</sub>. Second, the stability constants of Zn<sup>2+</sup>–EN complexes formed in the IL were determined from the concentration ratio [EN]/[Zn<sup>2+</sup>] dependence of <sup>15</sup>N NMR chemical shift values of the TFSA<sup>–</sup> N atom in the Zn<sup>2+</sup>/IL–EN solutions. In the IL, mono-, bis-, and tris-EN complexes are successively formed by 1:1 replacement of TFSA<sup>–</sup> anions coordinated with Zn<sup>2+</sup> by EN molecules with increasing EN content. Third, <sup>1</sup>H and <sup>13</sup>C NMR measurements with the help of density functional theory (DFT) calculations were made on [C<sub>2</sub>mIm][TFSA]–EN binary solvents as a function of <i>x</i><sub>EN</sub> to clarify key interactions to the mechanism of the complex formation. Fourth, the stability constants of Zn<sup>2+</sup>–EN complexes in the IL were compared with those in aqueous solutions. It was suggested that the hydrogen bonding of the EN molecule with the imidazolium ring H atoms and the TFSA<sup>–</sup> O atoms reduces the stability of the mono-EN complex in the IL. In contrast, the intracomplex hydrogen bonds between EN and TFSA<sup>–</sup> in the first coordination shell contribute to the higher stability of the bis-EN complex in the IL than that in aqueous solutions. The difference in the stability constants between the tris-EN complexes and hexaacetonitrile complexes, where acetonitrile (AN) molecules act as monodentate ligands, was interpreted in terms of the higher electron donicity of EN. Finally, to verify the present evaluation, the experimental <sup>13</sup>C NMR chemical shift values of EN molecules in the solutions were compared with the theoretical values calculated by DFT using the stability constants determined.","PeriodicalId":60,"journal":{"name":"The Journal of Physical Chemistry B","volume":null,"pages":null},"PeriodicalIF":2.8000,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"The Journal of Physical Chemistry B","FirstCategoryId":"1","ListUrlMain":"https://doi.org/10.1021/acs.jpcb.4c02590","RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
In bis(trifluoromethylsulfonyl)amide (TFSA–)-based ionic liquid (IL), 1-ethyl-3-methylimidazolium TFSA– ([C2mIm][TFSA]), the complex formation equilibria of zinc(II) ion (Zn2+) with ethylenediamine (EN) have been investigated. An EN molecule may coordinate with Zn2+ as a bidentate ligand. First, the formation of Zn2+–EN complexes in [C2mIm][TFSA] was confirmed from the difference of 1H and 13C NMR chemical shift values of EN molecules between [C2mIm][TFSA]–EN binary solvents and the 0.1 mol dm–3 Zn(TFSA)2/[C2mIm][TFSA]–EN solutions as a function of EN mole fraction xEN. Second, the stability constants of Zn2+–EN complexes formed in the IL were determined from the concentration ratio [EN]/[Zn2+] dependence of 15N NMR chemical shift values of the TFSA– N atom in the Zn2+/IL–EN solutions. In the IL, mono-, bis-, and tris-EN complexes are successively formed by 1:1 replacement of TFSA– anions coordinated with Zn2+ by EN molecules with increasing EN content. Third, 1H and 13C NMR measurements with the help of density functional theory (DFT) calculations were made on [C2mIm][TFSA]–EN binary solvents as a function of xEN to clarify key interactions to the mechanism of the complex formation. Fourth, the stability constants of Zn2+–EN complexes in the IL were compared with those in aqueous solutions. It was suggested that the hydrogen bonding of the EN molecule with the imidazolium ring H atoms and the TFSA– O atoms reduces the stability of the mono-EN complex in the IL. In contrast, the intracomplex hydrogen bonds between EN and TFSA– in the first coordination shell contribute to the higher stability of the bis-EN complex in the IL than that in aqueous solutions. The difference in the stability constants between the tris-EN complexes and hexaacetonitrile complexes, where acetonitrile (AN) molecules act as monodentate ligands, was interpreted in terms of the higher electron donicity of EN. Finally, to verify the present evaluation, the experimental 13C NMR chemical shift values of EN molecules in the solutions were compared with the theoretical values calculated by DFT using the stability constants determined.
期刊介绍:
An essential criterion for acceptance of research articles in the journal is that they provide new physical insight. Please refer to the New Physical Insights virtual issue on what constitutes new physical insight. Manuscripts that are essentially reporting data or applications of data are, in general, not suitable for publication in JPC B.