Selective extraction and transport of the [PtCl6]2- anion through outer-sphere coordination chemistry.

A series of tripodal receptors designed to recognise the outer coordination sphere of the hexachlorometallate anion [PtCl(6)](2-), and thus show selectivity for ion-pair formation over chloride binding, has been synthesised and characterised. The tripodal ligands contain urea, amido or sulfonamido hydrogen-bond donors, which are aligned to bind to the regions of greatest electron density along the faces and edges of the octahedral anion. The ligand structure incorporates a protonatable bridgehead nitrogen centre that provides a positive charge to ensure the solubility of a neutral 2:1 [LH](+)/[PtCl(6)](2-) complex in water-immiscible solvents.

Outer-sphere amidopyridyl extractants for zinc(ii) and cobalt(ii) chlorometallates.

Protonated amidopyridyl ligands show high selectivity for the extraction of [CoCl(4)](2-) or [ZnCl(4)](2-) over chloride ion into organic media via the formation of N-H and C-H hydrogen-bond donors to the outer coordination spheres of the chlorometallates.