Exceptional chemical and thermal stability of zeolitic imidazolate frameworks

Abstract

Twelve zeolitic imidazolate frameworks (ZIFs; termed ZIF-1 to -12) have been synthesized as crystals by copolymerization of either Zn(II) (ZIF-1 to -4, -6 to -8, and -10 to -11) or Co(II) (ZIF-9 and -12) with imidazolate-type links. The ZIF crystal structures are based on the nets of seven distinct aluminosilicate zeolites: tetrahedral Si(Al) and the bridging O are replaced with transition metal ion and imidazolate link, respectively. In addition, one example of mixed-coordination imidazolate of Zn(II) and In(III) (ZIF-5) based on the garnet net is reported. Study of the gas adsorption and thermal and chemical stability of two prototypical members, ZIF-8 and -11, demonstrated their permanent porosity (Langmuir surface area = 1,810 m(2)/g), high thermal stability (up to 550 degrees C), and remarkable chemical resistance to boiling alkaline water and organic solvents.

Scheme 1.

The bridging angles in metal IMs (1) and zeolites (2).

Fig. 1.

The single crystal x-ray structures of ZIFs. (Left and Center) In each row, the net is shown as a stick diagram (Left) and as a tiling (Center). (Right) The largest cage in each ZIF is shown with ZnN₄ tetrahedra in blue, and, for ZIF-5, InN₆ octahedra in red. H atoms are omitted for clarity.

Fig. 2.

The gas-sorption isotherms for prototypical ZIFs. (a) Nitrogen isotherm at 77 K for ZIF-8 sod. (b) Hydrogen isotherms at 77 K for ZIF-8 sod and ZIF-11 rho. (c) High-pressure hydrogen isotherm at 77 K for ZIF-8 sod.

Fig. 3.

The PXRD patterns for ZIF-8 samples measured during chemical stability tests. (a) In refluxing benzene at 80°C for up to 7 days. (b) In refluxing methanol at 65°C for up to 7 days. (c) In refluxing water at 100°C for up to 7 days. (d) In refluxing aqueous NaOH solution for up to 1 day.