Flexibility and anion exchange of [(X)@Pd2L4] cages for recognition of size and charge of polyatomic anions.

The self-assembly of Pd(NO3)2 with L (L = 1,2-bis(dimethyl(pyridin-3-yl)silyl)ethane) gives rise to [PdL2](NO3)2 in high yields. Anion exchange of [PdL2](NO3)2 with X- (X- = BF4-, ClO4-, and PF6-) changes the skeleton into a cage of [(X)@Pd2L4](X)3. Successive anion exchange of [(X)@Pd2L4](X)3 (X- = BF4-, ClO4-, and PF6-) with X- (X- = ReO4- and SiF62-) produces [(ReO4)@Pd2L4](ReO4)3 and [(SiF6)@Pd2L4](SiF6), respectively, irrespective of anion charge. The flexible nature and conformation of cages are significantly dependent on the nestled polyatomic anions. Thus, this system can be used as a molecular recognizer of the size and charge of ubiquitous polyatomic anions.