A Bowl-Type Dodecavanadate as a Halide Receptor

The dodecavanadate framework, [V 12 O 32 ] 4- , exhibits a unique bowl-type structure with an open molecular oxide cage having a cavity diameter of 4.4 Å, and different synthetic paths were required to construct the bowl-type structure with a different guest. A new dodecavanadate, {( n -C 4 H 9 ) 4 N} 4 [V 12 O 32 (CH 3 NO 2 )] ( 1 ), is synthesized with a nitromethane guest, which is stacked above the entrance of the hemisphere rather than fully occupying the cavity, and it enables a guest-capturing reaction, while retaining the anionic cage structure. Compound 1 is a good precursor for halide-centered dodecavanadates, {(C 2 H 5 ) 4 N} 5 [V 12 O 32 (X)] (X = Cl - ( 2 ), Br - ( 3 ), and I - ( 4 )). The position of the halide inside the cavity correlates with the ionic radius of the guest; the small chloride ion sat at the far bottom, and the large iodide floated at the entrance. The inclusion reaction rates were estimated through 51 V NMR time-course measurements in nitromethane. The reaction rates increase in the order I - < Br - < Cl - .