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Chapter 4 79
increasing feeding of 5-X-ipH2 the competition between BTC and 5-X-ip increases.
Subsequently, it is more difficult to rule out the presence of unreacted 5-X-ipH2 as the
reason of the decreasing SBET. In the same line of reasoning, the SBET of the samples 4a-c
dramatically decreased from 996 to 693 m 2 /g. Hence, the optimized incorporation of 5-
Br-ip can only reach up to 17% (4a). Notably, in our previous studies on the defectengineered
Cu-HKUST-1, the generation of mesopores was observed. [139] Curiously, in the
present case of the homologous Ru-DEMOFs, an opposite trend was observed, which
might be attributed to the preference of isolated defects rather than to the correlated
defects in the framework (Figure 4.17). During the formation of Ru-DEMOFs, the
substitution of [Ru]-L + DL ⇌ [Ru]-DL +L (L = AcO/BTC, DL = 5-X-ip) is kinetically
hindered by higher activation energy in comparison to that in the case of Cu-DEMOFs.
Consequently, the substitution is possibly much slower and lead to only isolated defects.
Figure 4.17. Schematic representation of point defects and correlated defects in DEMOFs. Figure
is provided by Dr. O. Halbherr.
4.2.3 XANES, XPS and UHV-FTIR studies: ruthenium oxidation state variation as
indication of defect type formation
As earlier mentioned, in our previous studies on doping of the Ru-MOF with defect pydc
linker, we have assigned the introduced local defects, according to Baiker et al., [136] as
modified Ru-paddlewheels with three coordinating BTC and one pydc linker, in which the
pyridyl-N site acts as a weakly binding ligator-site over the Ru-dimer. Such structural
irregularities are associated with (partially) missing linker function (i.e., carboxylate) and
consequently steric and electronic modification of the Ru-SBUs (see Figure 4.5).
Additionally, partial ruthenium reduction has been observed. Namely, apart from the
expected Ru 2+ and Ru 3+ (as in the parent Ru-MOF), we revealed also distinctly reduced