Collective Effects of Multiple Fluorine Atoms Causing -philic Characteristic within a Caged Polyoxometalate Framework

Perfluorination brings about distinctive properties arising from the unusual nature of the F element, which have been extensively developed in materials science and chemistry. Herein we report that the construction of F-rich inner space within a hollowed Mo132O372 cage ([Mo132O372(OCOR)30(H2O)72]42-) leads to the emergence of unique guest binding activities in encapsulation. Prominently, the trifluoroacetate-modified cage (R=CF3, 2) having as many as 90 F groups inside favors trapping cyclopentadiene (Cp), which is hardly trapped by the non-fluorinated counterpart (R=CH3, 1). Systematic studies using related hydrocarbons show that the amount of the encapsulated guest is correlated with the unsaturation degree of the guests, implying the involvement of the attractive interaction of the CF3-modified interior wall with the guest pi-electron clouds. Control experiments using the semi-fluorinated analogues (R=CF2H, CFH2) reveal that the perfluorination is a critical factor to facilitate the Cp encapsulation by 2, indicating that collective effects of polar C-F bonds spreading over the interior surface, rather than the polarity of the individual C-F bonds, are responsible. We also provide a successful example of the physical molecular confinement within the cage through the "ship-in-a-bottle" Diels-Alder reaction between trapped diene and dienophile. The polyanionic Mo132O372 architecture with perfluorinated interior surface favors capturing small non-aromatic guests carrying pi-bonds in water, which contrasts to the behavior of the non-fluorinated counterparts. Through systematic and control studies, it is revealed that collective effects of multiple C-F bonds, rather than the polarity of the individual C-F bonds, are responsible for the facile guest encapsulation.image