Very Large Breathing Effect in the First Nanoporous Chromium(III)-Based Solids: MIL-53 or Cr^III(OH)·{O₂C−C₆H₄−CO₂}·{HO₂C−C₆H₄−CO₂H}_x·H₂O_y

Abstract

The first three-dimensional chromium(III) dicarboxylate, MIL-53as or Cr(III)(OH) x [O(2)C-C(6)H(4)-CO(2)].[HO(2)C-C(6)H(4)-CO(2)H](0.75), has been obtained under hydrothermal conditions (as: as-synthesized). The free acid can be removed by calcination giving the resulting solid, MIL-53ht or Cr(III)(OH) x [O(2)C-C(6)H(4)-CO(2)]. At room temperature, MIL-53ht adsorbs atmospheric water immediately to give Cr(III)(OH) x [O(2)C-C(6)H(4)-CO(2)] x H(2)O or MIL-53lt (lt: low-temperature form, ht: high-temperature form). Both structures, which have been determined by using X-ray powder diffraction data, are built up from chains of chromium(III) octahedra linked through terephthalate dianions. This creates a three-dimensional structure with an array of one-dimensional large pore channels filled with free disordered terephthalic molecules (MIL-53as) or water molecules (MIL-53lt); when the free molecules are removed, this leads to a nanoporous solid (MIL-53ht) with a Langmuir surface area over 1500 m(2)/g. The transition between the hydrated form (MIL-53lt) and the anhydrous solid (MIL-53ht) is fully reversible and followed by a very high breathing effect (more than 5 A), the pores being clipped in the presence of water molecules (MIL-53lt) and reopened when the channels are empty (MIL-53ht). The thermal behavior of the two solids has been investigated using TGA and X-ray thermodiffractometry. The sorption properties of MIL-53lt have also been studied using several organic solvents. Finally, magnetism measurements performed on MIL-53as and MIL-53lt revealed that these two phases are antiferromagnetic with Néel temperatures T(N) of 65 and 55 K, respectively. Crystal data for MIL-53as is as follows: orthorhombic space group Pnam with a = 17.340(1) A, b = 12.178(1) A, c = 6.822(1) A, and Z = 4. Crystal data for MIL-53ht is as follows: orthorhombic space group Imcm with a = 16.733(1) A, b = 13.038(1) A, c = 6.812(1) A, and Z = 4. Crystal data for MIL-53lt is as follows: monoclinic space group C2/c with a = 19.685(4) A, b = 7.849(1) A, c = 6.782(1) A, beta = 104.90(1) degrees, and Z = 4.

Sustainable Separations of C4‐Hydrocarbons by Using Microporous Materials

“…For example, in gate‐opening transitions, a non‐porous material can become an open, microporous one 29. Similarly, “breathing” occurs when the pores expand (or contract) reversibly 30. In both cases, changing the framework structure will change the adsorption capacity 31.…”

Synthesis, spectroscopic and thermal studies of 2,3-naphthalenedicarboxylates of rare earth elements

“…In particular, dicarboxylate of benzene or naphthalene, with different coordination preferences, offers many advantages in the construction of highly porous and robust metalorganic frameworks [21,22].…”

Solvent-switchable continuous-breathing behaviour in a diamondoid metal–organic framework and its influence on CO2 versus CH4 selectivity

“…The structural changes occur predominantly through defined transitions between different crystalline states, a process commonly referred to as "breathing." 11,[14][15][16][17] This behaviour results in stepped adsorption isotherms, which may exhibit a hysteresis that can be exploited in gas capture or separation applications. [18][19][20] The most well-studied MOFs that exhibit such defined transitions are those with a pillared or columnar structure that contain 1D channels with a diamond or square cross-section, which compress or expand upon breathing in a manner analogous to that of a wine-rack.…”

“…18,24 The archetype of such materials is the MIL-53 family of MOFs ([M(X) [BDC] (M = trivalent Al, Cr, Fe, Ga; X = OH, F), which exhibit defined phase transitions between wide-pore (wp) and a narrow-pore (np) forms, upon desolvation and gas uptake. 14,15,20,[25][26][27] MOFs that exhibit large flexibility, but without defined transitions, are much rarer and are not well understood. The prototypical example of such continuous breathing behaviour, often referred to as "swelling," is the MIL-88 family of MOFs, which undergo very large changes in pore size on solvation/desolvation.…”