Host–guest assembly of ligand systems for metal ion complexation; synergistic solvent extraction of copper(ii) ions by N₃O₂-donor macrocycles and carboxylic or phosphinic acids

Abstract

Host-guest formation between N 3 O 2 -donor macrocyclic hosts and lipophilic organic acid guests (that are themselves potential metal-ion ligands/extractants) has been investigated and the implications of formation of such ligand assemblies for the binding of metal ions have been probed. The formation of 2 : 1 (organic acid : macrocycle) assemblies has been demonstrated using NMR titration experiments in deuterochloroform for 4-tertbutylbenzoic, palmitic, phenylphosphinic, diphenylphosphinic and salicylic acids, with evidence for the additional formation of 1 : 1 intermediates in some cases. Molecular adducts of this type have been used in solvent extraction (water/chloroform) experiments to define the effect of assembly formation on metal ion binding. From entropy considerations it was anticipated that the formation of particular host-guest species of the above type might result in enhanced metal ion binding (and hence enhanced metal ion extraction) -a consequence of the fact that the components of the coordination sphere are, at least in part, assembled for complex formation. Using a range of assemblies of the above type, enhanced (synergistic) extraction of Cu() ions was confirmed in all cases. Adducts of 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane and 1,12,15-triaza-3,4:9,10-bis(4Ј-tert-butylbenzo)-5,8dioxacycloheptadecane with 4-tert-butylbenzoic acid and salicylic acid have been isolated and their solid-state structures (and 1 : 2 stoichiometries) confirmed by X-ray diffraction.

Cooperative Binding of Calix[4]pyrrole–Anion Complexes and Alkylammonium Cations in Halogenated Solvents

“…[1][2][3][4][5][6] A few of these receptors have also been studied in conjunction with cation receptors in the form of binary mixtures, [7][8][9][10][11][12][13] or even more effectively as ditopic ion-pair receptors, [5,14,15] and have been shown to bind ion pairs as contact ion-pairs [7,[16][17][18][19] or spatially separated ion pairs. [20] An advantage of an ion-pair receptor over a simple ion receptor is that the number of competing interactions in solution (i.e., the formation of cation-anion pairs) is reduced.…”

A study of the complexation and extraction of Cu(ii) sulfate and Ni(ii) sulfate by N3O2-donor macrocycles

“…We have shown recently that metal extraction by macrocyclic ligands of the type L 1 and L 2 is significantly enhanced by using a synergistic combination of the macrocycle, L, and a lipophilic organic acid, RXH, and that these combinations can form assemblies, [LH n (RX) n ], containing the complete donor set needed by the metal cation. 11 Under these circumstances the system can then operate as a cation-exchange extractant. 2…”

Host–guest assembly of ligand systems for metal ion complexation. Synergistic solvent extraction of copper(ii) and silver(i) by 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclodecane in combination with carboxylic acids

“…For example, it has been recently shown that the use of host-guest assemblies of type [LH 2 (RX) 2 ] between lipophilic carboxylic or phosphinic acids [RXH] and dibenzo-substituted N 3 O 2 -donor macrocycles [L] incorporating secondary amine groups in a chloroform phase in each case resulted in enhanced (synergistic) solvent extraction of copper(II) from aqueous solution. 4 ‡ † Electronic supplementary information (ESI) available: Further experimental details for the (non-tracer) solvent extraction studies. See http://www.rsc.org/suppdata/dt/b4/b412255k/ ‡ The situation may be broadly compared with the observed enhancement of coordination when pendant arms incorporating additional donors are appended covalently to a macrocyclic core.…”