Network Flexibility: Control of Gate Opening in an
Isostructural Series of Ag-MOFs by Linker Substitution
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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 (Ag<sub>2</sub>N<sub>4</sub>) can be obtained under solvothermal conditions from
substituted triazolyl benzoate linkers and AgNO<sub>3</sub> or Ag<sub>2</sub>SO<sub>4</sub>; they exhibit 2-fold network interpenetration
with <b>lvt</b> 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