FLEXIBILITY OF MOFS

Flexibility and guest-responsive systems. The access to the porosity of rigid microporous materials such as zeofites is normally restricted by the dimensions of the windows giving access to the porosity, rather than the size of the cavities themselves. It has become clear, however, that the permanent porosity of MOFs can behave quite differently to that of the rigid zeolites. Unlike zeolites, carbons, or oxides, a number of coordination compounds have frameworks that possess a noticeable degree of... 

In summary, the adsorption behaviour of MOFs is of interest because of their large pore volumes, and the novel properties of their organic-lined pores. Furthermore, the reactivity and flexibility of their structures gives rise to reversible uptake of H-bonding molecules with recrystallisation, breathing ... 

When appHed in the asymmetric epoxidation of 2,2-dimethyl-2H-chromene, this MOF was less active than the homogeneous salen complex, but more stable over time, as the immobihzation of the Mn(salen) complexes precludes oxidation of one metal center by another. Immobilization decreases the flexibility of the hgands, explaining the slight decrease in enantioselectivity compared to the free complex. While a small loss of catalytically inactive Mn was observed after each ran, the enantioselectivity remained constant however, upon prolonged use of this catalyst, the outer layers of the MOF crystals were gradually damaged by oxidation. This... 

As the second example, mesh-adjustable molecular sieve (MAMS) proposed and prepared by Ma et al. are another class of flexible MOFs with a temperature-dependent gas-selective adsorption performance [124, 125]. MAMSs are a series of MOFs, including MAMS-1 (Ni8(5-bbdc)6( X3-OH)4, bbdc = 5-tert-butyl-1,3-benzenedicarboxylate), MAMS-2 (Zn(bbpdc), bbpdc = 4-tert-butyl-3,5-dicarboxylate), MAMS-3 (Co(bbpdc)), andMAMS-4 (Cu(bbpdc)). Gas adsorption measurements showed that these materials have unique gas-selective adsorptive properties at different temperature, for example, MAMS-2 showed a good selectivity of H2/N2 at 77 K and O2/N2 at 87 K, respectively. Molecular sieving effects of four MAMSs are very similar, which are affected by the temperature. It is clear that when the size difference of the two gases is very small, a molecular sieve with... 

In a broad sense, a nanoreactor is to be understood as the nanosized container in which a chemical reaction is carried out. As discussed previously, the pores of MOFs have the right dimensions (from a few angstroms to a few nanometers) to be considered nanoreactors. However, it is evident that the confinement of the reaction in such a limited space will affect the molecular movement and the interactions between the molecules hosted inside (and between the molecules and the reactor walls), as well as the conformational flexibility of the guest. Therefore, regardless of whether or not the MOF participates actively in the reaction (by providing the active sites that catalyze the chemical transformation). 

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