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

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.