Self-assembled metallogels formed from N,N′,N′′-tris(4-pyridyl)trimesic amide in aqueous solution induced by Fe(<scp>iii</scp>)/Fe(<scp>ii</scp>) ions

Abstract

In this work, we report self-assembled metallogels formed from a ligand of trimesic amide, N,N',N''-tris(4-pyridyl)trimesic amide (TPTA), induced by Fe(III)/Fe(II) ions. TPTA is difficult to dissolve in water even in the presence of some metal ions such as Cu(2+), Co(2+), Ni(2+), K(+), Na(+) and Mg(2+) under heating, and it exhibits no gelation ability. Interestingly, upon heating TPTA can be dissolved easily in aqueous solution containing Fe(3+)/Fe(2+), and subsequently self-assembled into metallogels after cooling. The metallogels could also be formed in aqueous solutions of mixed metal ions containing Fe(3+)/Fe(2+), indicating that the other metal ions do not affect the formation of Fe(III)-TPTA and Fe(II)-TPTA metallogels. The high selectivity of metallogel formation to Fe(3+)/Fe(2+) may be used for application in the test of Fe(3+)/Fe(2+). The metallogels obtained are characterized by scanning electron microscopy, Fourier transform infrared spectra, nuclear magnetic resonance spectra, rheological measurements and scanning tunneling microscopy. The results indicate that TPTA can self-assemble into fibrous aggregates in Fe(3+)/Fe(2+) aqueous solution through the metal-ligand interactions and intermolecular hydrogen bonding. This kind of metallogel also possesses good mechanical properties and thermoreversibility.