Network Flexibility: Control of Gate Opening in an Isostructural Series of Ag-MOFs by Linker Substitution

Abstract

An isostructural series of 15 structurally flexible microporous silver metal-organic frameworks (MOFs) is presented. The compounds with a dinuclear silver core as secondary building unit (Ag2N4) can be obtained under solvothermal conditions from substituted triazolyl benzoate linkers and AgNO3 or Ag2SO4; they exhibit 2-fold network interpenetration with lvt topology. Besides the crystal structures, the calculated pore size distributions of the microporous MOFs are reported. Simultaneous thermal analyses confirm the stability of the compounds up to 250 °C. Interconnected pores result in a three-dimensional pore structure. Although the porosity of the novel coordination polymers is in the range of only 20-36%, this series can be regarded as a model system for investigation of network flexibility, since the pore diameters and volumes can be gradually adjusted by the substituents of the 3-(1,2,4-triazol-4-yl)-5-benzamidobenzoates. The pore volumes of selected materials are experimentally determined by nitrogen adsorption at 77 K and carbon dioxide adsorption at room temperature. On the basis of the flexible behavior of the linkers a reversible framework transformation of the 2-fold interpenetrated network is observed. The resulting adsorption isotherms with one or two hysteresis loops are interpreted by a gate-opening process. Due to external stimuli, namely, the adsorptive pressure, the materials undergo a phase transition confirming the structural flexibility of the porous coordination polymer.

Reversible Phase Transition of Porous Coordination Polymers

“…Pressure‐induced phase transformations can occur in a wide range of materials, including gold nanoribbons, perovskites, chalcogenide semiconductors, silicon, and MOFs . Importantly, the functionalities of MOFs may also be tuned by pressure.…”

Flexible Metal–Organic Frameworks: Recent Advances and Potential Applications

“…Then, “dynamic behavior” has been used to describe the transformation process between the multistable states of flexible MOFs. Based on the different structures of flexible MOFs, multitudinous dynamic behaviors, for example, the expansion/shrinkage of the framework, the opening/closing of pores, or the reversible change of the physicochemical properties, have been realized. More importantly, these fascinating characteristics of flexible MOFs have great potential in storage, separation, sensing, and many other applications, which makes them more interesting in the classes of MOFs …”

A novel three-dimensional copper(I) cyanide coordination polymer constructed from various bridging ligands: synthesis, crystal structure and characterization

“…Over the past few decades, cyanide-bridged metal coordination polymers have received increasing attention due to their various structures and intriguing magnetic behaviours (Pike, 2012;Zhou et al, 2009;Xu et al, 2016), porous (Zhang et al, 2014;Furukawa et al, 2013;Herm et al, 2013) and luminescence properties (Rocha et al, 2011;Heine & Mü ller-Buschbaum, 2013;Guillerm et al, 2014;Eddaoudi et al, 2015), through the judicious choice of metal centres, as well as bridging or ancillary ligands (Li et al, 2013(Li et al, , 2014Handke et al, 2014). Notably, the cyanide ion is the simplest species containing carbon and nitrogen, and involves a combination of donation by the highest occupied molecular orbital (HOMO) and acceptance ( back-bonding) by the lowest unoccupied molecular orbital (LUMO).…”