Controlling Catenation In MOFs

The chirality and lattice interpenetration, also known as catenation, of metal-organic framework (MOF) compounds can be controlled through the chirality of organic ligands or by the nature of the solvent (J. Am. Chem. Soc. 2008, 130, 13834). MOFs—crystalline porous compounds composed of metal clusters connected by organic linkers—are used in gas separation, catalysis, and other areas. Chiral MOFs with pores and channels measuring several nanometers in diameter could lead to new applications in chiral separations and asymmetric catalysis. Some chiral MOFs have already been synthesized, but often the pores are constricted due to catenation, which is similar to interlocking rings. Wenbin Lin and Liqing Ma of the University of North Carolina, Chapel Hill, have demonstrated that catenation can be suppressed by controlling either of two synthesis parameters. In one case the group reacted copper compounds with enantiopure tetracarboxylate ligands and formed a noncatenated chiral MOF with channels measuring up to 3.2 nm in diameter. When they prepared MOFs from the racemic mixture of ligands, the structure depended on the solvent. Dimethylformamide led to catenated crystals with reduced pore size. MOFs grown in diethylformamide, however, were noncatenated.