Microporous, Crystalline, and Water-Processable Framework Materials of Organic Amphiphile Salts

Abstract

Porous framework materials are of major importance for a wide range of technologies. Nevertheless, many of these materials lack processibility as they are typically synthesized under rather harsh conditions and obtained as microcrystalline powders that cannot easily be coated or deposited from solution. Herein, a new approach to water-processable metal–organic framework materials is presented. The materials are based on amphiphilic organic building blocks consisting of polar carboxylate groups and non-polar alkyl chains connected to a rigid aromatic core. The amphiphilic building blocks assemble to porous framework structures via bonding to kinetically labile sodium ions from concentrated aqueous solution. The obtained crystalline materials, termed amphiphile salt frameworks, are thermally and mechanically stable (some derivatives up to 365 °C and up to at least 4000 bar hydrostatic pressure), exhibit persistent microporous channels accessible to several gases (N2, CO2, propane, propylene, n-butane), and can be reversibly assembled/disassembled by crystallization from or dissolution in water. Systematic variation of the hydrophobic side chains of the amphiphile building blocks allows extracting structure-property relationships and first design rules for this new class of water-processable microporous framework materials.