the complex Fe(3-OMeSalEen) 2 ]PF 6 [173] (H-3-OMeSalEen is a condensation
product of 3-methoxysalicylaldehyde and N-ethylethylenediamine), the influence
of PTM on the structural changes is observed in this system (cf. Sect. 2.2.4). The
three media used were Alcatel 100 (a paraffin-based mineral oil from Alcatel),
Fluorinert FC77 (a perfluorocarbon liquid from 3 M) and Daphne 7,373 (a mixture
of olefin oligomers from Idemitsu Kosan Global). The change in the PTM results in
modification of the spin-crossover curves on decompression, thought to be caused
by damage to the crystals on compression and subsequent decompression in these
different fluids. Although the structural distortions observed in the aforementioned
Fe-based spin-crossover complexes resulted in a distortion of the individual molecules, the spin transition in the molecular complex [Fe(dpp) 2 (NCS) 2 ]Ápy
(dpp ¼ dipyrido[3,2-α:2
0 3
0 -c]phenazine) gives rise to a ‘scissor’-like motion, as
coined by the authors, which not only results in a distortion of the individual
molecules but also results in NLC behaviour, with the isothermal compressibility
K a ¼ À30(4) TPa
À1 [174].
4.5 Metal Organic Frameworks and Coordination Polymers
According to IUPAC, metal-organic frameworks (or MOFs) are defined as ‘coordination networks with organic ligands containing potential voids’ [175]. In MOFs, a
three-dimensional framework is generated by the reticular assembly of metal ions or
clusters and multi-dentate organic bridges into an infinite polymeric network. The
ordered nature of the framework often results in the formation of crystals or
polycrystalline powders, although amorphous and liquid MOFs have also recently
been reported [176, 177]. Porosity is a common but not pervasive feature of MOFs,
with void space accounting for 10–70% of the unit cell volume, with the pores
ranging from microporous (d < 2 nm) to nanoporous (d ¼ 2–50 nm). From the
diverse array of framework architectures, chemical composition, porosities and
functionalities possible, a taxonomy of MOFs has emerged, including zeolitic
imidazolate frameworks (ZIFs), Matériaux de l’Institut Lavoisier (MILs) and
isoreticular frameworks (IRMOFs). Materials in these classes are some of the most
studied at high pressure. Appropriate selection of the PTM is important in the study
of porous metal organic framework and in particular with respect to their structural
integrity and pressure response. Small, penetrating media, for example (such as
gases or liquids), can enter the pores of the framework at elevated pressure. Penetration of methanol into the pores of ZIF-8 at elevated pressure was demonstrated in
the work by Moggach et al. [178], in which a solvent-dependent pressure-induced
‘gate-opening’ rotation of the imidazolate linker was observed. This transition
proved pivotal in understanding the maximum amount of guest N 2 uptake under
much milder pressure (bars). The phase transition observed at 1.47 GPa in a MeOH:
EtOH mixture was established to be the same transition observed on exposing a
polycrystalline powder of ZIF-8 to N2 gas at 0.4 bar [3]. Prior to this pressure study,
ZIF-8 was actually considered a rather rigid MOF, with other classes of MOFs, such
186
S. A. Moggach and I. D. H. Oswald
product of 3-methoxysalicylaldehyde and N-ethylethylenediamine), the influence
of PTM on the structural changes is observed in this system (cf. Sect. 2.2.4). The
three media used were Alcatel 100 (a paraffin-based mineral oil from Alcatel),
Fluorinert FC77 (a perfluorocarbon liquid from 3 M) and Daphne 7,373 (a mixture
of olefin oligomers from Idemitsu Kosan Global). The change in the PTM results in
modification of the spin-crossover curves on decompression, thought to be caused
by damage to the crystals on compression and subsequent decompression in these
different fluids. Although the structural distortions observed in the aforementioned
Fe-based spin-crossover complexes resulted in a distortion of the individual molecules, the spin transition in the molecular complex [Fe(dpp) 2 (NCS) 2 ]Ápy
(dpp ¼ dipyrido[3,2-α:2
0 3
0 -c]phenazine) gives rise to a ‘scissor’-like motion, as
coined by the authors, which not only results in a distortion of the individual
molecules but also results in NLC behaviour, with the isothermal compressibility
K a ¼ À30(4) TPa
À1 [174].
4.5 Metal Organic Frameworks and Coordination Polymers
According to IUPAC, metal-organic frameworks (or MOFs) are defined as ‘coordination networks with organic ligands containing potential voids’ [175]. In MOFs, a
three-dimensional framework is generated by the reticular assembly of metal ions or
clusters and multi-dentate organic bridges into an infinite polymeric network. The
ordered nature of the framework often results in the formation of crystals or
polycrystalline powders, although amorphous and liquid MOFs have also recently
been reported [176, 177]. Porosity is a common but not pervasive feature of MOFs,
with void space accounting for 10–70% of the unit cell volume, with the pores
ranging from microporous (d < 2 nm) to nanoporous (d ¼ 2–50 nm). From the
diverse array of framework architectures, chemical composition, porosities and
functionalities possible, a taxonomy of MOFs has emerged, including zeolitic
imidazolate frameworks (ZIFs), Matériaux de l’Institut Lavoisier (MILs) and
isoreticular frameworks (IRMOFs). Materials in these classes are some of the most
studied at high pressure. Appropriate selection of the PTM is important in the study
of porous metal organic framework and in particular with respect to their structural
integrity and pressure response. Small, penetrating media, for example (such as
gases or liquids), can enter the pores of the framework at elevated pressure. Penetration of methanol into the pores of ZIF-8 at elevated pressure was demonstrated in
the work by Moggach et al. [178], in which a solvent-dependent pressure-induced
‘gate-opening’ rotation of the imidazolate linker was observed. This transition
proved pivotal in understanding the maximum amount of guest N 2 uptake under
much milder pressure (bars). The phase transition observed at 1.47 GPa in a MeOH:
EtOH mixture was established to be the same transition observed on exposing a
polycrystalline powder of ZIF-8 to N2 gas at 0.4 bar [3]. Prior to this pressure study,
ZIF-8 was actually considered a rather rigid MOF, with other classes of MOFs, such
186
S. A. Moggach and I. D. H. Oswald