Thermally Driven Catch-and-Release of CoCl 2 .

A heat-driven catch-and-release strategy for CoCl 2 capture is described. It is based on the use of an immobilized neutral dicyclohexylacetamide-based receptor L supported on polystyrene (PS- L ). An X-ray diffraction analysis of a single crystal of L ·CoCl 2 revealed an ion-pair complex comprising a hexacoordinated cobalt cation [ L ·Co] 2+ and a tetrachlorocobaltate anion [CoCl 4 ] 2- . Temperature dependent binding was seen, as inferred from UV-vis spectroscopic studies. Fits to the van't Hoff equation yielded values of Δ H ° = 12.4 kJ/mol and Δ S ° = 56.0 J/K·mol for L + CoCl 2 , and Δ H ° = 16.5 kJ/mol and Δ S ° = 85.0 J/K·mol for PS- L + CoCl 2 in 95% ethanol. Consequently, cobalt capture and release are mediated by heating and cooling, respectively. The material PS- L exhibits a preference for binding cobalt over manganese and nickel as inferred from Langmuir-Freundlich isotherm analyses that revealed binding constants of K LF = 88.5 M -1 for CoCl 2 , 52.7 M -1 for MnCl 2 , and 49.7 M -1 for NiCl 2 . In a simulated ion mixture containing equimolar CoCl 2 , MnCl 2 , and NiCl 2 , ICP-MS analyses served to confirm that cobalt was selectively enriched to 52 mol % (from an initial level of ca. 32 mol %) after one catch-and-release cycle and 76.6% after three cycles. Our experimental results were validated by density functional theory calculations, which also show stronger binding of Co over Mn and Ni to L .