Recognition and order of multiple sidechains by metal-organic framework enhances the separation of hexane isomers

Porous materials perform molecular sorting, separation and transformation by interaction between their framework structures and the substrates. Proteins also interact with molecules to effect chemical transformations, but rely on the precise sequence of the amino acid building units along a common polypeptide backbone to maximise their performance. Design strategies that positionally order sidechains over a defined porous framework to diversify the internal surface chemistry would enhance control of substrate processing. Here we show that different sidechains can be ordered over a metal-organic framework through recognition of their distinct chemistries during synthesis. The sidechains are recognised because each one forces the common building unit that defines the backbone of the framework into a different conformation in order to form the extended structure. The resulting sidechain ordering affords hexane isomer separation performance superior to that of the same framework decorated only with sidechains of a single kind. The separated molecules adopt distinct arrangements within the resulting modified pore geometry, reflecting their strongly differentiated environments precisely created by the ordered sidechains. The development of frameworks that recognize and order multiple sidechain functionality by conformational control offers tailoring of the internal surfaces within families of porous materials to direct interactions at the molecular level. The ordering of multiple sidechains on a metal-organic framework is achieved by the assembly of linkers that differ only in the appended functional groups at a chiral centre. The strain induced by the functional groups defines the conformation of each linker and drives their ordering in the crystal structure of the framework. The pore environments formed by this assembly have well-defined adsorption sites for hexane isomers and enhance their separation. image