Flexible metal-organic framework

Some metal-organic frameworks (MOF) display large structural changes as a response to external stimuli, and such modifications of their structure can, in turn, lead to drastic changes in their physical and chemical properties. Such stimuli-responsive MOFs are generally referred to as a flexible metal-organic frameworks.[1] They can also be called dynamic metal-organic framework, stimuli-responsive MOFs,[2] multi-functional MOFs,[3] or soft porous crystals.[4]

Demonstration of the flexibility of the MIL-53 metal-organic framework. Adapted from Hou et al.[5]

Formally, a metal-organic framework is a coordination network with organic ligands containing potential voids. A coordination network is a coordination compound extending, through repeating coordination entities, in one dimension, but with cross-links between two or more individual chains, loops, or spiro-links, or a coordination compound extending through repeating coordination entities in two or three dimensions. A coordination polymer is a coordination compound with repeating coordination entities extending in one, two, or three dimensions.[6]

Generally, this kind of material has a well-defined structure, but sometimes some external stimuli can affect its structure, resulting in a different structure without breaking the overall network. A variety of external stimuli like heat, light, solvent, an electric field, magnetic field, etc. can act upon a metal-organic framework, can act to change its internal structure, and can facilitate the transformation process. This structural transformation generally occurs by bond breaking/making, change of coordination number of the metal ion, change of coordination mode of ligand, ligand length squeezing, solvent exchange, solvent removal, etc.[7]

One often discussed example of flexible metal-organic framework is the family of MIL-53 materials,[8] featuring one-dimensional diamond-shaped pores that can expand or contract upon stimulation, such as adsorption of guest molecules (solvent, water, gases, etc.), changes in temperature, and mechanical pressure.

References
  1. Schneemann, A.; Bon, V.; Schwedler, I.; Senkovska, I.; Kaskel, S.; Fischer, R. A. (2014-07-22). "Flexible metal–organic frameworks". Chemical Society Reviews. 43 (16): 6062–6096. doi:10.1039/C4CS00101J. ISSN 1460-4744.
  2. Coudert, François-Xavier (24 March 2015). "Responsive Metal–Organic Frameworks and Framework Materials: Under Pressure, Taking the Heat, in the Spotlight, with Friends". Chemistry of Materials. 27 (6): 1905–1916. doi:10.1021/acs.chemmater.5b00046.
  3. Silva, Patrícia; Vilela, Sérgio M. F.; Tomé, João P. C.; Almeida Paz, Filipe A. (2015). "Multifunctional metal–organic frameworks: from academia to industrial applications". Chemical Society Reviews. 44 (19): 6774–6803. doi:10.1039/C5CS00307E. ISSN 0306-0012.
  4. Horike, Satoshi; Shimomura, Satoru; Kitagawa, Susumu (2009-11-23). "Soft porous crystals". Nature Chemistry. 1 (9): 695–704. doi:10.1038/nchem.444. ISSN 1755-4349.
  5. Hou, Jingwei; Ashling, Christopher W.; Collins, Sean M.; Krajnc, Andraž; Zhou, Chao; Longley, Louis; Johnstone, Duncan N.; Chater, Philip A.; Li, Shichun; Coulet, Marie-Vanessa; Llewellyn, Philip L. (2019-06-12). "Metal-organic framework crystal-glass composites". Nature Communications. 10 (1): 1–10. doi:10.1038/s41467-019-10470-z. ISSN 2041-1723. PMC 6561910. PMID 31189892.
  6. Batten, Stuart R.; Champness, Neil R.; Chen, Xiao-Ming; Garcia-Martinez, Javier; Kitagawa, Susumu; Öhrström, Lars; O'Keeffe, Michael; Suh, Myunghyun Paik; Reedijk, Jan (2012-04-02). "Coordination polymers, metal–organic frameworks and the need for terminology guidelines". CrystEngComm. 14 (9): 3001–3004. doi:10.1039/C2CE06488J. ISSN 1466-8033.
  7. Halder, Arijit; Ghoshal, Debajyoti (2018-03-05). "Structure and properties of dynamic metal–organic frameworks: a brief accounts of crystalline-to-crystalline and crystalline-to-amorphous transformations". CrystEngComm. 20 (10): 1322–1345. doi:10.1039/C7CE02066J. ISSN 1466-8033.
  8. Loiseau, Thierry; Serre, Christian; Huguenard, Clarisse; Fink, Gerhard; Taulelle, Francis; Henry, Marc; Bataille, Thierry; Férey, Gérard (2004-03-19). "A Rationale for the Large Breathing of the Porous Aluminum Terephthalate (MIL-53) Upon Hydration". Chemistry – A European Journal. 10 (6): 1373–1382. doi:10.1002/chem.200305413. ISSN 0947-6539.

See also
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