Comparative solvent extraction (water/chloroform) studies of Ni(II) and Cu(II) employing a dinonyl-substituted N3O2-donor macrocycle (L2) as extractant have been undertaken from sulfate, chloride, nitrate and acetate-containing aqueous media. Contrary to expectations, efficient extraction of both metal sulfates was observed, the degree of extraction being comparable (or slightly enhanced) relative to that observed for each of the other anionic systems. X-Ray diffraction studies of [NiL1(H2O)3]SO4 x 4H2O and [CuL1(H2O)]SO4 x 6.67 H2O (where L1 is the unsubstituted derivative of L2) show that each complex occurs as a hydrogen-bonded 'cluster', with the sulfate anions involved in hydrogen bonded networks that incorporate ligand amine protons and water molecules; in the copper complex, which adopts a dimeric arrangement, simultaneous sulfate binding to a copper site is also present. In each complex the macrocyclic ligand fails to coordinate via its ether oxygen donors but instead is arranged so that the metal ion and sulfate anions are somewhat shielded hydrophobically from the exterior of the complex cluster assembly.

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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.

Combining cation- and anion-binding functionalities in a salen-type extractant leads to multiple loading of ZnCl(2). Zn(ii) cations are bound by the salen N(2)O(2)(2-) donor set, and chlorozincate anions are associated with protonated pendant amine groups.

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