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 – .

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closed-V12 with diethylamine, and the structure transformation was confirmed by using the isolated intermediate. Thereverse transformation from opened-V12 to closed-V12 was also proceeded by addition of trifluoroacetic acid. The geometrical difference between closed-V12 and opened-V12 is reflected in the reactivity difference to the external reagents, and it was demonstrated by examining the chloride removal reaction by silver cation. Incorporated chloride was preserved in the closed-V12 cage even in the presence of silver cation. Contrary, chloride in opened-V12 was removed asAgCl by silver cation. In addition, by the reaction of the chloride-free opened-V12 with a quantitative amount of {Et4N}Cl retrieved opened-V12, showing the capability of opened-V12 to recapture a guest chloride in the cavity. The transformation between two isomeric dodecavanadate structures is regarded as a move of a molecular mitt to catch a ball and secure it.

SynopsisA bowl-shaped polyoxovanadate, [V 12 polyoxovanadate framework, without V(IV) valence state. The two-step process, involving transformation of a disk to a bowl, then transformation from the bowl to a ball, enables the incorporation of a guest anion inside the ball. An alternative route from a hexadecavanadate, which avoids the use of hydrogen cyanide, is also described.

A dodecavanadate, [V O ] , is an inorganic bowl-type host with a cavity entrance with a diameter of 4.4 Å in the optimized structure. Linear, bent, and trigonal planar anions are tested as guest anions and the formation of host-guest complexes, [V O (X)] (X=CN , OCN , NO , NO , HCO , and CH CO ), were confirmed by X-ray crystallographic analyses and a V NMR spectroscopy study. The degree of distortion of the bowl from a regular to an oval shape depends on the type of guest anion. In V NMR spectroscopy, all chemical shifts of the host-guest complexes are clearly shifted after guest incorporation. The incorporation reaction rates for OCN , NO , HCO , and CH CO are much larger than those of NO and halides. The incorporated nonspherical molecular anions in the dodecavanadate host are easily dissociated or exchanged for other anions, whereas spherical halides in the host are preserved without dissociation, even in the presence of the tested anions.