Amides do not always work: observation of guest binding in an amide-functionalised porous host

An amide-functionalised metal organic frame-work (MOF) material, MFM-136, shows a high CO2 uptake of 12.6 mmol g-1 at 20 bar and 298 K. MFM-136 is the first example of acylamide pyrimidyl isophthalate MOF without open metal sites, and thus provides a unique platform to study guest bind-ing, particularly the role of free amides. Neutron diffraction reveals that, surprisingly, there is no direct binding between the adsorbed CO2/CH4 molecules and the pendant amide group in the pore. This observation has been confirmed un-ambiguously by inelastic neutron spectroscopy. This suggests that introduction of functional groups solely may not neces-sarily induce specific guest-host binding in porous materials, but it is a combination of pore size, geometry, and functional group that leads to enhanced gas adsorption properties

Reversible adsorption and confinement of nitrogen dioxide within a robust porous metal-organic framework

Nitrogen dioxide (NO2) is a major air pollutant causing significant environmental and health problems. We report reversible adsorption of NO2 in a robust metal–organic framework. Under ambient conditions, MFM-300(Al) exhibits a reversible NO2 isotherm uptake of 14.1 mmol g−1, and, more importantly, exceptional selective removal of low-concentration NO2 (5,000 to <1 ppm) from gas mixtures. Complementary experiments reveal five types of supramolecular interaction that cooperatively bind both NO2 and N2O4 molecules within MFM-300(Al). We find that the in situ equilibrium 2NO2 ↔ N2O4 within the pores is pressure-independent, whereas ex situ this equilibrium is an exemplary pressure-dependent first-order process. The coexistence of helical monomer–dimer chains of NO2 in MFM-300(Al) could provide a foundation for the fundamental understanding of the chemical properties of guest molecules within porous hosts. This work may pave the way for the development of future capture and conversion technologies

Optimal Binding of Acetylene to a Nitro-Decorated Metal-Organic Framework

We report the first example of crystallographic observation of acetylene binding to −NO2 groups in a metal–organic framework (MOF). Functionalization of MFM-102 with −NO2 groups on phenyl groups leads to a 15% reduction in BET surface area in MFM-102-NO2. However, this is coupled to a 28% increase in acetylene adsorption to 192 cm3 g–1 at 298 K and 1 bar, comparable to other leading porous materials. Neutron diffraction and inelastic scattering experiments reveal the role of −NO2 groups, in cooperation with open metal sites, in the binding of acetylene in MFM-102-NO2