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108 Chapter 4
4.3 Defects Engineering in [Cu3(BTC)2]n: Effect of the synthetic parameters
To date, the introduction of defects into the [M3(BTC)2]n structure has been achieved via
mixed-linker solid solutions approach for frameworks where M = Cu or Ru. [136, 138-140] By
varying the DLs, simultaneously mixed with H3BTC during the synthesis, DEMOFs with a
general formula [M3(BTC)2-x(DL)x]n could be obtained. Interestingly, in spite of the very
similar structural long range order of the DEMOFs, local point defects can influence the
metal environment at the PW and also enhance structural properties such as porosity.
Different types of defect A and B in Ru-DEMOFs as well as their influence on the sorption
and catalytic properties have already been described in Chapter 4.2. More interestingly,
incorporation of pydc into [M3(BTC)2]n, the generation of reduced metal sites was found
in both the formed Ru-DEMOFs ([Ru3(BTC)2-x(pydc)xYy]n) [138] and Cu-DEMOFs
([Cu3(BTC)2-x(pydc)x]n) [139] However, only in the former case, CO2 → CO dissociative
chemisorption (“reduction”) at low temperature (90 K) under UHV conditions was
achieved. Utilizing 5-OH-ip as DL during the MOF synthesis, the mesopores prefer to be
generated in Cu-DEMOFs rather than in Ru-DEMOFs. Moreover, even the modification of
the doping level of the same DL in Cu-DEMOF can control the formation of the framework
with micropores or mesopores. [139] Recently, Hupp et al. reported the formation of
missing Cu 2+ node defects in the obtained Cu-DEMOF with ip incorporation, [140] while
defect type A (modified PW units) related Cu + formation was observed in the Cu-DEMOF
with pydc or other 5-X-ip(X = OH, CN, NO2) incorporation. [139] With regard to these
accounts, it is essential to understand the structural complexity of DEMOFs, which will be
beneficial to tailor their advanced properties. Therefore, in comparison with rather
complicated Ru-(DE)MOFs system and following the description of Cu-DEMOFs reported
by Hupp et al. and Fang et al., the relative simple [Cu3(BTC)2]n has been chosen as a
candidate here to be incorporated by ip DL under different synthetic conditions (e.g.
solvent, nature of the metal salts). Systematically study on the formation of M-DEMOFs
variants of [M3(BTC)2]n structure, namely, types of local defects (i.e. the generation of
reduced metal-sites or not), their origin as well as the dependence on variation of the
synthetic conditions will be investigated.