A Comparison of the Selectivity of Extraction of [PtCl6]2– by Mono-, Bi-, and Tripodal Receptors That Address Its Outer Coordination Sphere

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• 作者：Rebecca J. Warr ; Katherine J. Bell ; Anastasia Gadzhieva ; Rafel Cabot ; Ross J. Ellis ; Jy Chartres ; David K. Henderson ; Eleni Lykourina ; A. Matthew Wilson ; Jason B. Love ; Peter A. Tasker ; Martin Schröder
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：June 20, 2016
• 年：2016
• 卷：55
• 期：12
• 页码：6247-6260
• 全文大小：695K
• 年卷期：0
• ISSN：1520-510X

文摘

Extraction and binding studies of [PtCl<sub>6sub>]<sup>2–sup> are reported for 24 mono-, bi-, and tripodal extractants containing tris(2-aminoethyl)amine (TREN) or tris(3-aminopropyl)amine (TRPN) scaffolds. These reagents are designed to recognize the outer coordination sphere of [PtCl<sub>6sub>]<sup>2–sup> and to show selectivity over chloride anion under acidic conditions. Extraction from 0.6 M HCl involves protonation of the N-center in tertiary amines containing one, two, or three urea, amide, or sulfonamide hydrogen-bond donors to set up the following equilibrium: 2L<sub>(org)sub> + 2H<sup>+sup> + [PtCl<sub>6sub>]<sup>2–sup> ⇌ [(LH)<sub>2sub>PtCl<sub>6sub>]<sub>(org)sub>. All reagents show higher Pt loading than trioctylamine, which was used as a positive control to represent commercial trialkylamine reagents. The loading of [PtCl<sub>6sub>]<sup>2–sup> depends on the number of pendant amides in the extractant and follows the order tripodal > bipodal > monopodal, with urea-containing extractants outperforming amide and sulfonamide analogues. A different series of reagents in which one, two, or three of the alkyl groups in tris-2-ethylhexylamine are replaced by 3-N′-hexylpropanamide groups all show a comparably high affinity for [PtCl<sub>6sub>]<sup>2–sup> and high selectivity over chloride anion in extractions from aqueous acidic solutions. <sup>1sup>H NMR titration of three extractants [LH·Cl] with [(Oct<sub>4sub>N)<sub>2sub>PtCl<sub>6sub>] in CDCl<sub>3sub> provides evidence for high selectivity for [PtCl<sub>6sub>]<sup>2–sup> over chloride for tri- and bipodal extractants, which show higher binding constants than a monopodal analogue.