DFT simulations [190]. Introduction of defects into the structure has also provided
additional control over the compressibility and pressure at which amorphisation of
the MOF occurs. A method to create defects in these materials has been the addition
of controlled equivalents of trifluoroacetic acid modulator during preparation of
UiO-66 to introduce missing-ligand defects in the framework, lowering the average
coordination number of the Zr 6 O 4 (OH) 4 nodes [194]. Decreasing the connection of
the net from 12c (non-defected) to 9c (defected) lowers the amorphisation onset
pressure from 0.4 to 0.3 GPa and decreases the bulk modulus of the material (K 0 )
from ~26 GPa to ~12 GPa (K 0 was calculated with 8 data points up to 0.175 GPa).
Further decrease of the net connection to 8c increased the bulk modulus to ~14 GPa
due to the suspected transition of the network topology.
As is typical for porous materials, guest-loaded UiO-type frameworks are resistive to compression. Pressure-induced pore filling of UiO-67 and UiO-abdc with
methanol increases the bulk moduli of the materials up to 30-fold that of the native
framework, going from 13.4 GPa to 174 GPa for UiO-67 and 16.8 GPa to 580 GPa
for UiO-abdc from theoretical simulations and nanoindentation measurements.
Maximum occupation of the pores was reached by ~1.2 GPa, signalled by no further
volumetric increase of the unit cell (Fig. 17). Notably, both materials were unaffected by further compression up to 2.4 GPa (UiO-67) or 4.8 GPa (UiO-abdc). Slight
compression of the unit cell is typical for MOFs with fully occupied pores; the total
resistance to compression of these UiO-frameworks is therefore unusual.
Fig. 17 Graph of percentage change in volume vs. pressure (GPa) for UiO-abdc in methanol
(circles), FC-70 (diamonds), and UiO-67 in methanol (squares), FC-70 (triangles). Figure taken
from Angew. Chem. Int. Ed., 2016, Volume: 128, Issue: 7, Pages: 2447–2451, DOI: (https://doi.
org/10.1002/ange.201509352) [190]
188
S. A. Moggach and I. D. H. Oswald
additional control over the compressibility and pressure at which amorphisation of
the MOF occurs. A method to create defects in these materials has been the addition
of controlled equivalents of trifluoroacetic acid modulator during preparation of
UiO-66 to introduce missing-ligand defects in the framework, lowering the average
coordination number of the Zr 6 O 4 (OH) 4 nodes [194]. Decreasing the connection of
the net from 12c (non-defected) to 9c (defected) lowers the amorphisation onset
pressure from 0.4 to 0.3 GPa and decreases the bulk modulus of the material (K 0 )
from ~26 GPa to ~12 GPa (K 0 was calculated with 8 data points up to 0.175 GPa).
Further decrease of the net connection to 8c increased the bulk modulus to ~14 GPa
due to the suspected transition of the network topology.
As is typical for porous materials, guest-loaded UiO-type frameworks are resistive to compression. Pressure-induced pore filling of UiO-67 and UiO-abdc with
methanol increases the bulk moduli of the materials up to 30-fold that of the native
framework, going from 13.4 GPa to 174 GPa for UiO-67 and 16.8 GPa to 580 GPa
for UiO-abdc from theoretical simulations and nanoindentation measurements.
Maximum occupation of the pores was reached by ~1.2 GPa, signalled by no further
volumetric increase of the unit cell (Fig. 17). Notably, both materials were unaffected by further compression up to 2.4 GPa (UiO-67) or 4.8 GPa (UiO-abdc). Slight
compression of the unit cell is typical for MOFs with fully occupied pores; the total
resistance to compression of these UiO-frameworks is therefore unusual.
Fig. 17 Graph of percentage change in volume vs. pressure (GPa) for UiO-abdc in methanol
(circles), FC-70 (diamonds), and UiO-67 in methanol (squares), FC-70 (triangles). Figure taken
from Angew. Chem. Int. Ed., 2016, Volume: 128, Issue: 7, Pages: 2447–2451, DOI: (https://doi.
org/10.1002/ange.201509352) [190]
188
S. A. Moggach and I. D. H. Oswald