Tailoring the breathing behavior of functionalized MIL-53(Al,M)-NH2 materials by using the mixed-metal concept

Increasing the Complexity in the MIL‐53 Structure: The Combination of the Mixed‐Metal and the Mixed‐Linker Concepts

“…Both, MIL‐53(Al 0.8 Cr 0.2 )‐NH 2 (100) and MIL‐53(Al 0.8 Fe 0.2 )‐NH 2 (100) showed isotherms with a significant difference between the adsorption and the desorption branches (Figure 6 c, d). As reported earlier, [7a] we proposed that a breathing transition occurred only at high relative pressures, which would explain the missing S‐shaped adsorption isotherm that is usually related to a breathing behavior and the difference of the adsorbed volume between the adsorption and desorption branches.…”

“…Thus, the nitrogen physisorption measurements indicated that an inflexible lp‐form seemed to be favorable for MIL‐53(Al 0.8 V 0.2 )‐NH 2 (40). Initially, the scandium analogues were expected to be the least interesting materials during nitrogen physisorption, since MIL‐53(Al 0.8 Sc 0.2 )‐NH 2 (100) did not show any significant uptake of nitrogen in our previous study [7a] . However, the additional incorporation of terephthalate did have a tremendous influence on the nitrogen physisorption isotherms (Figure 6 a).…”

“…The previously developed direct synthesis procedures for MIL‐53(Al 0.8 M 0.2 )‐NH 2 materials (M=Sc, V, Cr or Fe) were used for the synthesis of mixed‐metal/mixed‐linker materials (Scheme 1). [7a] For each of the metal combinations, different ratios of terephthalate/2‐aminoterephthalate were used during the synthesis without any other changes to the procedures. The obtained MIL‐53(Al 0.8 M 0.2 )‐NH 2 (X) materials were labeled according to the percentage of 2‐aminoterephthalate with respect to the total amount of linkers.…”

“…A clear step in the adsorption isotherm and, thus, a breathing transition was present for the already earlier reported MIL‐53(Al 0.8 V 0.2 )‐NH 2 (100) (Figure 6 b). [7a] Upon the incorporation of terephthalate, the step flattened for MIL‐53(Al 0.8 V 0.2 )‐NH 2 (80) and MIL‐53(Al 0.8 V 0.2 )‐NH 2 (60) and disappeared for MIL‐53(Al 0.8 V 0.2 )‐NH 2 (40). The latter material showed an isotherm, which is typically observed for rigid microporous solids.…”

“…Therefore, all MIL‐53(Al 0.8 M 0.2 )‐NH 2 (X) materials were modified with maleic anhydride (Scheme 2) to show that the mixed‐metal/mixed‐linker concept is compatible with post‐synthetic modifications and to investigate whether different combinations or ratios of components have an influence on the modification process. In analogy to our previous study, [7a] all materials were activated at 130 °C in vacuum before adding a solution of maleic anhydride in acetonitrile to the dehydrated materials.…”