A Reversibly pH-Switchable Open/Closed Cage Constructed from Triangular Polyoxometalate Hybrid [(C7H7AsO3)6W12O36]12- Cluster Anions Exhibiting Supramolecular Chirality.

A new nanosized polyoxometalate modified by benzylarsonate ligands, [(C7H7AsO3)6W12O36]12- (1a), was successfully isolated and structurally characterized as Na2(C2H8N)4H6[(C7H7AsO3)6W12O36]·30H2O (1). Controlled protonation of 1a led it to self-reorganize into isomer cage cluster [(C7H7AsO3)6W12O30(OH)4(H2O)2]4- (2a) with an organic ligand arranging in "half-open" mode. The reversibly switchable cage transform was monitored by 1H NMR. Also, the origin of the solid supramolecular chirality in the crystal 1 and the aggregation process of 1a were preliminarily studied.