Anion Receptor Design: Exploiting Outer-Sphere Coordination Chemistry To Obtain High Selectivity for Chloridometalates over Chloride

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• 作者：Innis Carson ; Kirstian J. MacRuary ; Euan D. Doidge ; Ross J. Ellis ; Richard A. Grant ; Ross J. Gordon ; Jason B. Love ; Carole A. Morrison ; Gary S. Nichol ; Peter A. Tasker ; A. Matthew Wilson
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：September 8, 2015
• 年：2015
• 卷：54
• 期：17
• 页码：8685-8692
• 全文大小：467K
• ISSN：1520-510X

文摘

High anion selectivity for PtCl₆^{2鈥?/sup> over Cl鈥?/sup> is shown by a series of amidoamines, R1R2NCOCH₂CH₂NR3R4 (L1 with R1 = R4 = benzyl and R2 = R3 = phenyl and L3 with R1 = H, R2 = 2-ethylhexyl, R3 = phenyl and R4 = methyl), and amidoethers, R1R2NCOCH₂CH₂OR3 (L5 with R1 = H, R2 = 2-ethylhexyl and R3 = phenyl), which provide receptor sites which extract PtCl₆2鈥?/sup> preferentially over Cl鈥?/sup> in extractions from 6 M HCl solutions. The amidoether receptor L5 was found to be a much weaker extractant for PtCl₆2鈥?/sup> 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鈥?/sup>. 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鈥揌 or O鈥揌 groups are also readily available to form hydrogen bonds to the PtCl₆2鈥?/sup> ion, in addition to the array of polarized C鈥揌 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)₂PtCl₆]. The DFT calculations and the X-ray structure indicate that all LH+ receptors present an array of polarized C鈥揌 groups to the large, charge diffuse PtCl₆2鈥?/sup> anion resulting in high selectivity of extraction of PtCl₆2鈥?/sup> over the large excess of chloride.}