title: Ditopic receptors containing urea groups for solvent extraction of Cu(ii) salts.
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)]2structure 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 CuSO4and CuCl2from water into chloroform with high selectivity over the corresponding Co(ii), Ni(ii) and Zn(ii) salts.
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. david.esteban@udc.es.
authors.forename: Israel
authors.initials: I
authors.lastname: Carreira-Barral
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. david.esteban@udc.es.
authors.forename: Marta
authors.initials: M
authors.lastname: Mato-Iglesias
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. david.esteban@udc.es.
authors.forename: Andrés
authors.identifier: http://orcid.org/0000-0001-8548-9658
authors.initials: A
authors.lastname: de Blas
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. david.esteban@udc.es.
authors.forename: Carlos
authors.identifier: http://orcid.org/0000-0002-6989-9654
authors.initials: C
authors.lastname: Platas-Iglesias
authors.affiliation: The School of Chemistry at Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK. peter.tasker@ed.ac.uk.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Tasker
authors.affiliation: Universidade da Coruña, Centro de Investigacións Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Facultade de Ciencias, 15071, A Coruña, Galicia, Spain. david.esteban@udc.es.
authors.forename: David
authors.identifier: http://orcid.org/0000-0001-6270-1660
authors.initials: D
authors.lastname: Esteban-Gómez