Anion Receptor Design: Exploiting Outer-Sphere Coordination Chemistry To Obtain High Selectivity for Chloridometalates over Chloride
Anion Receptor Design: Exploiting Outer-Sphere Coordination Chemistry To Obtain High Selectivity for Chloridometalates over Chloride
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DOI：
10.1021/acs.inorgchem.5b01317
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发表时间：
2015-09-07
影响因子：
4.6
通讯作者：
Wilson, A. Matthew
中科院分区：
文献类型：
--
作者：
Carson, Innis;MacRuary, Kirstian J.;Wilson, A. Matthew
一系列酰氨基胺 (RRNCOCH2CH2NRR4)-R-1-N-2-R-3（L1 中 R-1 = R-4 = 苄基，R-2 = R-3 = 苯基，L3 中 R-1 = H、R-2 = 2-乙基己基、R-3 = 苯基和 R-4 = 甲基）显示了 PtCl62- 相对于 Cl- 的高阴离子选择性，并且酰胺醚，(RRNCOCH2CH2OR3)-R-1-N-2（L5，其中 R-1 = H，R-2 = 2-乙基己基，R3 = 苯基），其提供在从 6 M HCl 溶液中萃取时优先萃取 PtCl62- 而非 Cl- 的受体位点。发现酰胺醚受体 LS 对 PtCl62- 的萃取剂比其酰胺胺类似物弱得多。密度泛函理论计算表明，这是由于酰胺醚难以质子化以产生阳离子受体LH+，而不是后者与PtCl62-的结合较弱。最稳定的受体形式 LH+ 含有互变异构体，其中添加的质子与酰胺氧原子形成分子内氢键，形成六元质子螯合物。色散校正的 DFT 计算似乎表明，酰胺胺配体的配体构象转变为复合物中的开放互变异构体状态，使得除了极化的 C-H 键阵列之外，阳离子 N-H 或 O-H 基团也很容易与 PtCl62- 离子形成氢键。然而，L1 的质子螯合态和非螯合互变异构体态之间的预测能量差异很小，并且前者存在于组装体 [(L1H)(2)PtCl6] 的 X 射线晶体结构中。 DFT 计算和 X 射线结构表明，所有 LH+ 受体都对大的电荷扩散 PtCl62- 阴离子呈现一系列极化的 C-H 基团，导致 PtCl62- 相对于大量过量的氯化物的提取具有高选择性。
High anion selectivity for PtCl62- over Cl- is shown by a series of amidoamines, (RRNCOCH2CH2NRR4)-R-1-N-2-R-3 (L1 with R-1 = R-4 = benzyl and R-2 = R-3 = phenyl and L3 with R-1 = H, R-2 = 2-ethylhexyl, R-3 = phenyl and R-4 = methyl), and amidoethers, (RRNCOCH2CH2OR3)-R-1-N-2 (L5 with R-1. = H, R-2 = 2-ethylhexyl and R3 = phenyl), which provide receptor sites which extract PtCl62- preferentially over Cl- in extractions from 6 M HCl solutions. The amidoether receptor LS was found to be a much weaker extractant for PtCl62- than its amidoamine analogues. Density functional theory calculations indicate that this is due to the difficulty in protonating the amidoether to generate a cationic receptor, LH+, rather than the latter showing weaker binding to PtCl62-. The most stable forms of the receptors, LH+, contain a tautomer in which the added proton forms an intramolecular hydrogen bond to the amide oxygen atom to give a six-membered proton chelate. Dispersion-corrected DFT calculations appear to suggest a switch in ligand conformation for the amidoamine ligands to an open tautomer state in the complex, such that the cationic N-H or O-H groups are also readily available to form hydrogen bonds to the PtCl62- ion, in addition to the array of polarized C-H bonds. The predicted difference in energies between the proton chelate and nonchelated tautomer states for L1 is small, however, and the former is found in the X-ray crystal structure of the assembly [(L1H)(2)PtCl6]. The DFT calculations and the X-ray structure indicate that all LH+ receptors present an array of polarized C-H groups to the large, charge diffuse PtCl62- anion resulting in high selectivity of extraction of PtCl62- over the large excess of chloride.