Ditopic receptors containing urea groups for solvent extraction of Cu(ii) salts?

Dalton Transactions Pub Date: 2017-02-15 DOI: 10.1039/C7DT00093F

Abstract

The ditopic receptor L3 [1-(2-((7-(4-(tert-butyl)benzyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)phenyl)-3-(3-nitrophenyl)urea] containing a macrocyclic cyclen unit for Cu(II)-coordination and a urea moiety for anion binding was designed for recognition of metal salts. The X-ray structure of [CuL3(SO4)] shows that the sulfate anion is involved in cooperative binding via coordination to the metal ion and hydrogen-bonding to the urea unit. This behaviour is similar to that observed for the related receptor L1 [1-(2-((bis(pyridin-2-ylmethyl)amino)methyl)phenyl)-3-(3-nitrophenyl)urea], which forms a dimeric [CuL1(μ-SO4)]2 structure in the solid state. In contrast, the single crystal X-ray structure of [ZnL3(NO3)2] contains a 1?:?2 complex (metal?:?anion) where one anion coordinates to the metal and the other is hydrogen-bonded to the urea group. Spectrophotometric titrations performed for the [CuL3(OSMe2)]2+ complex indicate that this system is able to bind a wide range of anions with an affinity sequence: MeCO2? > Cl? > H2PO4? > Br? > NO2? > HSO4? > NO3?. Lipophilic analogues of L1 and L3 extract CuSO4 and CuCl2 from water into chloroform with high selectivity over the corresponding Co(II), Ni(II) and Zn(II) salts.

Graphical abstract: Ditopic receptors containing urea groups for solvent extraction of Cu(ii) salts
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