Lotus-Root-like One-Dimensional Polymetallocages with Drastic Void Adaptability Constructed from 4,4′-Bis(1,2,4-triazol-1-ylmethyl)biphenyl and Zn(II) or Co(II) and Their Fluorescein Encapsulation Properties

The reaction of 4,4'-bis(1,2,4-triazol-1-ylmethyl)biphenyl (L) with Zn(NOP3)(2)center dot 6H(2)O or Co(NO3)(2)center dot 6H(2)O in the presence of NH4PF6 in water-methanol or water-acetone produced both {[ZnL3](PF6)(2)(H2O)(2)}(n) (1) or {[CoL3](PF6)(2)(H2O)(2)}(n) (2). The metal ions in both complexes coordinate with six identical N atoms from six different ligands in an ideal octahedral environment where each ligand binds to two metal ions. Both complexes are one-dimensional triple-helical chains each containing an empty lotus-root-structured polymetallocage. The metallocage in I is fully empty, while the cage in 2 contains two water molecules. However, metallocages in 1 have a void volume of similar to 200 angstrom(3), which is much smaller than the 1020 angstrom(3) void in 2. The void in 2 is comparable to the size of fluorescein. Both complexes are capable of encapsulating fluorescein anion in pH 9 aqueous solution to form {C20H10O5 subset of [ML3]}(n), where C20H10O52- is fluorescein dianion, and M is Zn or Co. The encapsulation occurs via anion exchange. The cages in 1 are increased drastically to fit the size of fluorescein due to the flexibility of ligand, while in 2 the cages have no discernible change after fluorescein encapsulation due to a perfect match between the cavity size in 2 and the fluorescein. Fluorescein encapsulated 1 and 2 have identical powder X-ray diffraction patterns, indicating that they have similar structures after fluorescein encapsulation. Both complexes show fluorescence after fluorescein encapsulation.