Chromium terephthalate

Ferey, G., Mellot-Draznieks, C., Serre, C., et al, A chromium terephthalate-based solid with unusually large pore volumes and surface area. Science 2005, 309, 2040-2042, correction 2005, 310, 1119. 

Fig. 22 Expanded (anhydrous) and contracted (hydrated) forms of the chromium terephthalate MIL-53, drawn to the same scale.81 Gray spheres denote carbon and red oxygen, with Cr06 octahedra in green. Reproduced with permission from Serre et at. Copyright 2002, American Chemical...

Figure 7.12 The chromium terephthalate MIL-53 (Cr0H(02CC6H4C02)) is a very flexible structure. When heated to remove all adsorbed moleeules the structure is very open (above left). Carbon dioxide adsorption at 304 K proceeds stepwise (below). At pressures below ca. 2 bar, the structure adapts by contraction of the channels to coordinate CO2 molecules chemisorbed at the structural hydroxide group, and this structure remains stable until pressures higher than 2 bar, when it opens to take large volumes of CO2 into the channels.

Chromium terephthalate (MIL-101) has been used for synthesis in MOF development. It exhibits good thermal stability and large pore channels, which promotes mass transport. MIL-101 can be functionalised with palladium or gold nanoparticles, for example, due to the presence of acidic ccxjrdinatively unsaturated sites present on the MOF. This leads to applications of chromium MOFs in hydrogenation reactions and oxidative catalysis. 

Chromium has a large contribution to the MOF arena due to the fact that it has created the largest pore-sized metal catalysts yet known. Ferey created a crystal structure for porous chromium terephthalate, MIL-101, with very large pore sizes and surface area. Its zeotype cubic structure has an enormous cell volume ( 702 000 A ), a hierarchy of extra-large pore sizes (30 to 34 A), and a Langmuir surface area for N2 of 5900 300 m This... 

Llewellyn PL, Bourrrelly S, Sene C et al (2006) How hydration drastically improves adsorption selectivity for CO2 over CH4 in the flexible chromium terephthalate MIL-53. Angew Chem Int Ed 4 7751-7754... 

In the search of porous inorganic-organics hydrides solids (see other contributions in this volume) which display several potential applications, the development of new synthesis routes is of crucial importance because the conventional methods generally consist of hydro- or solvo-thermal processes that require up to several days. The cubic chromium terephthalate Cr3F(H20)20[C6R4(C02)2]3 (MIL-101), for instance, has been successfully synthesized using a microwave solvothermal process. Owing to the faster dissolution of the precursors and/or the condensation process, the MIL-101 can be obtained even after 1 min of irradiation at 210 °C. Finally, a well crystallized material is obtained for 40 min of irradiation at 210 °C while the conventional method is performed at 220 °C for 10 h. The very rapid synthesis of MIL-101 leads to nanosized crystals that result in an improvement of the sorption properties of benzene. 

Hong, D. Y, Hwang, Y K., Serre, C., Ferey, G., and Chang, J. S. Porous chromium terephthalate MIL-101 with coordinatively unsaturated sites Surface functionalization, encapsulation, sorption and catalysis. Adv Fund Mater 19,1537-1552 (2009). 

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