Self-assembly and anion encapsulation properties of cavitand-based coordination cages

Two novel classes of cavitand-based coordination cages 7a-j and 8a-d have b een synthesized via self-assembly procedures. The main factors controlling cage self-assembly (CSA) have been identified in (i) a P-M-P angle close to 90 degrees between the chelating ligand and the metal precursor, (ii) Pd a nd Pt as metal centers, (iii) a weakly coordinated counterion, and (iv) pre organization of the tetradentate cavitand ligand. Calorimetric measurements and dynamic H-1 and F-19 NMR experiments indicated that CSA is entropy dri ven. The temperature range of the equilibrium cage-oligomers is determined by the level of preorganization of the cavitand component. The crystal stru cture of cage 7d revealed the presence of a single triflate anion encapsula ted. Guest competition experiments revealed that the encapsulation preferen ce of cages 7b,d follows the order BF4- > CF3SO3_ >> PF6- at 300 K. ES-MS e xperiments coupled to molecular modeling provided a rationale for the obser ved encapsulation selectivities. The basic selectivity pattern, which follo ws the solvation enthalpy of the guests, is altered by size and shape of th e cavity, allowing the entrance of an ancillary solvent molecule only in th e case of BF4-.