Method Adds Metals To Frameworks Selectively

A new procedure for tailoring metal-organic framework (MOF) compounds is poised to make this highly popular class of useful solids even more useful (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja4050828). MOFs are porous crystals composed of metal ions or clusters connected by organic linkers. The materials’ extreme surface areas and porosities have led to numerous record-breaking demonstrations and some commercialization in gas separation and storage as well as catalysis. Tailoring MOFs’ internal surfaces with chemically active metal ions can enhance the materials’ performance. Yet most methods for adding metals call for solution-phase treatments that can plug the crystals’ pores with unwanted solvents and reagents. Gas-phase deposition could eliminate the need to purify MOFs, but it provides little control over the deposited metals’ distribution. Northwestern University chemists Omar K. Farha and Joseph T. Hupp and coworkers have shown that these problems can be sidestepped by using atomic layer deposition. In this process, sequentially pulsed precursors react to form one atomic layer of products per pulse sequence. The team used diethyl­zinc and trimethylaluminum to decorate microscopic MOF channels with Zn and Al, respectively. They showed that unlike native MOFs, the metal-decorated versions are active catalysts for modified aldol condensations.