Maseda Mikio, Takamuku Toshiyuki
Analytical Research Center for Experimental Sciences, Saga University, Honjo-machi, Saga 840-8502, Japan.
Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan.
J Phys Chem B. 2024 Oct 3;128(39):9500-9511. doi: 10.1021/acs.jpcb.4c02590. Epub 2024 Sep 19.
In bis(trifluoromethylsulfonyl)amide (TFSA)-based ionic liquid (IL), 1-ethyl-3-methylimidazolium TFSA ([CmIm][TFSA]), the complex formation equilibria of zinc(II) ion (Zn) with ethylenediamine (EN) have been investigated. An EN molecule may coordinate with Zn as a bidentate ligand. First, the formation of Zn-EN complexes in [CmIm][TFSA] was confirmed from the difference of H and C NMR chemical shift values of EN molecules between [CmIm][TFSA]-EN binary solvents and the 0.1 mol dm Zn(TFSA)/[CmIm][TFSA]-EN solutions as a function of EN mole fraction . Second, the stability constants of Zn-EN complexes formed in the IL were determined from the concentration ratio [EN]/[Zn] dependence of N NMR chemical shift values of the TFSA N atom in the Zn/IL-EN solutions. In the IL, mono-, bis-, and tris-EN complexes are successively formed by 1:1 replacement of TFSA anions coordinated with Zn by EN molecules with increasing EN content. Third, H and C NMR measurements with the help of density functional theory (DFT) calculations were made on [CmIm][TFSA]-EN binary solvents as a function of to clarify key interactions to the mechanism of the complex formation. Fourth, the stability constants of Zn-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 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.
在基于双（三氟甲基磺酰）亚胺（TFSA）的离子液体（IL）1-乙基-3-甲基咪唑鎓双（三氟甲基磺酰）亚胺（[CmIm][TFSA]）中，研究了锌（II）离子（Zn）与乙二胺（EN）的络合物形成平衡。一个EN分子可以作为双齿配体与Zn配位。首先，通过比较[CmIm][TFSA]-EN二元溶剂和0.1 mol dm Zn(TFSA)/[CmIm][TFSA]-EN溶液中EN分子的H和C NMR化学位移值随EN摩尔分数的变化，证实了[CmIm][TFSA]中Zn-EN络合物的形成。其次，根据Zn/IL-EN溶液中TFSA N原子的N NMR化学位移值对[EN]/[Zn]浓度比的依赖性，确定了IL中形成的Zn-EN络合物的稳定常数。在IL中，随着EN含量的增加，通过EN分子以1:1的比例取代与Zn配位的TFSA阴离子，依次形成单-、双-和三-EN络合物。第三，借助密度泛函理论（DFT）计算，对[CmIm][TFSA]-EN二元溶剂进行了H和C NMR测量，作为 的函数，以阐明对络合物形成机制的关键相互作用。第四，将IL中Zn-EN络合物的稳定常数与水溶液中的稳定常数进行了比较。结果表明，EN分子与咪唑鎓环H原子和TFSA O原子之间的氢键降低了IL中单-EN络合物的稳定性。相反，第一配位层中EN和TFSA之间的络合物内氢键有助于IL中双-EN络合物比水溶液中具有更高的稳定性。三-EN络合物和六乙腈络合物（其中乙腈（AN）分子作为单齿配体）之间稳定常数的差异，根据EN较高的给电子性进行了解释。最后，为了验证当前的评估，将溶液中EN分子的实验C NMR化学位移值与使用确定的稳定常数通过DFT计算的理论值进行了比较。
