Article Review · PNAS · 2006

ZIF-8: Zeolite Logic, MOF Chemistry

PaperExceptional chemical and thermal stability of zeolitic imidazolate frameworks
AuthorsK. S. Park, Z. Ni, A. P. Cote, J. Y. Choi, R. Huang, F. J. Uribe-Romo, H. K. Chae, M. O'Keeffe, O. M. Yaghi
PublishedPNAS, 2006
DOI10.1073/pnas.0602439103
Read the Original Paper ↗

The standard objection to MOFs circa 2005 was blunt: beautiful crystals, dead on contact with water. Park and colleagues answered with a design argument rather than a patch. Because the metal-imidazolate-metal bond angle of about 145 degrees mirrors the Si-O-Si angle of zeolites, zinc and cobalt imidazolates crystallize into zeolite topologies, and the resulting zeolitic imidazolate frameworks inherit something of zeolite toughness.

The demonstrations were theatrical by materials-chemistry standards. ZIF-8 survived a week in boiling water, refluxing benzene and methanol, and even 8 molar aqueous NaOH at 100 degrees, while holding thermal stability to roughly 550 C. Twelve ZIFs were reported, mapping imidazolate chemistry onto sodalite and other classic nets, with ZIF-8's 3.4 angstrom windows opening into 11.6 angstrom cavities, dimensions that later made it the default material for size-selective separations and an early commercial product.

A quarter of the field's subsequent ZIF literature is footnotes to this paper, including the correction literature: later studies showed ZIF-8's apparent window is effectively larger than 3.4 angstroms because the linkers swing, the famous gate-opening effect, and that its hydrothermal armor has limits under acidic or CO2-saturated aqueous conditions. The stability claims are robust but were occasionally over-generalized to the whole ZIF family, some members of which are far frailer.

As a piece of scientific rhetoric this paper is close to perfect: identify the field's central weakness, propose a structural principle that addresses it, then torture the material publicly until skeptics concede. Every applications-minded MOF researcher should know it cold.

Reviewer's VerdictThe stability breakthrough. ZIF-8 became one of the most manufactured MOFs for good reason.

This review reflects the independent opinion of Team LR at MOFsResearch.com. It is an educational commentary on the cited publication and is not affiliated with or endorsed by the original authors or publisher. Verify all figures against the original paper before use.