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H 2<br />
adsorbed, mmol/g<br />
98 Chapter 4<br />
8<br />
6<br />
4<br />
2<br />
parent Ru-MOF<br />
4a<br />
0<br />
0 200 400 600 800 1000<br />
P, mbar<br />
Figure 4.34. H 2 isotherms measured at 77 K for the parent Ru-MOF and Ru-DEMOF 4a (17%) with<br />
5-Br-ip DL. Black circles – parent Ru-MOF; blue triangles – 4a.<br />
Another indication of the suggested counter acting effects of the defect sites is the<br />
comparison of the CO2 and H2 uptakes at 2a, 2b and 4a with the parent Ru-MOF (Figures<br />
4.33, 4.34, 4.35 and 4.36). However, the variations are too small to be regarded as<br />
significant. Still, some assumptions can be concluded, which afford us some ideas on the<br />
future design of DEMOFs towards considerable optimization of sorption properties. In<br />
spite of the creation of defects A with Ru δ+ -sites, the rather small change of the H2 and CO2<br />
uptake in the sample of 4a (17% 5-Br-ip) might be contributed to the functional –Brgroups<br />
from the 5-Br-ip linker at the defect-sites. One the one hand, they may create larger<br />
steric hindrances (compared to the other DLs used) blocking, thus, the access for the gas<br />
molecules in spite of the modified paddlewheels with more rooms around Ru-sites. On the<br />
other hand, weaker H2 binding affinity has been found in MOFs composed of ligands with<br />
electron-withdrawing groups. [229-230] Although this influence caused from the interaction<br />
between H2 and ligands is smaller in comparison with the strong one of H2-M sites, it can<br />
be one reason of the observation study in the sample 4a.
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