Structural Changes and Coordinatively Unsaturated Metal Atoms on Dehydration of Honeycomb Analogous Microporous Metal–Organic Frameworks

Abstract

Porous metal-organic framework compounds with coordinatively unsaturated metal sites on the inner surface of the pores promise to be valuable adsorbents and catalyst systems, either in industrial applications or as model systems to study interactions with guest molecules. The dehydration process of two isostructural microporous coordination polymers, [M2(dhtp)(H2O)2].8 H2O, termed CPO-27-M (M=Co, Zn; H(4)dhtp=2,5-dihydroxyterephthalic acid) was investigated by in situ variable temperature X-ray diffraction. Both compounds contain accessible coordination sites at the metal after complete removal of the solvent. However, despite the analogy of their crystal structures, they behave differently during dehydration. For CPO-27-Co, water desorption is a smooth topotactic process of second order with no concomitant space group change and no increase in microstrain, which is beneficial for the applicability of the material. Removal of the water propagates from the center of the channels outwards. The coordinating water molecule at the metal desorbs only when almost all the bulk water in the pores has disappeared. In contrast, discontinuities in the powder pattern of CPO-27-Zn indicate the occurrence of first-order transitions. The crystal structures of four of the five individual phases could be determined. The structure of the intermediate phase occurring just before the framework is completely evacuated was elusive in respect to full structure solution and refinement, but it is most probably related to the removal of the axis of threefold symmetry. The zinc-based material experiences a significant amount of strain.

High drug-loading nanomedicines: progress, current status, and prospects

“…96 MOFs consist of transition metal ions/clusters and multidentate organic ligands, and are typically synthesized via coordinationdirected self-assembly processes under mild conditions ( Figure 4). 97 Over the past two decades, MOFs have been applied in photonics, 98 catalysis, [99][100][101] biosensors, 102,103 gas storage, [104][105][106][107] and drug delivery. [108][109][110][111] For drug delivery, the high drug-loading capacity of MOFs relies largely on three factors: 1) high surface area (3,100-5,900 m 2 /g) 108 and large, regular, accessible cages and tunnels; 2) good physicochemical stability in circulation and quick stimuli 109,113 -effectively in hexane solution.…”

Metal-dioxidoterephthalate MOFs of the MOF-74 type: Microporous basic catalysts with well-defined active sites

“…We here report that surprisingly, M 2 dobdc type MOFs are active catalysts for such reactions, with intrinsically basic properties. M 2 dobdc represents a series of isostructural compounds, denominated CPO-27-M by Dietzel et al, [16][17][18][19][20] or MOF-74 for the zinc compound by Rosi et al [21] (CPO: Coordination Polymer of Oslo; M = Ni, Co, Zn, Mg, Mn). The structure consists of metal oxide chains connected by the 2,5-dioxidoterephthalate linker (dobdc 4-) forming a honeycomblike structure with large, one-dimensional hexagonal pores of 1.1-1.2 nm in diameter ( Figure 1(top)).…”

Understanding the adsorption mechanism of noble gases Kr and Xe in CPO-27-Ni, CPO-27-Mg, and ZIF-8

“…The water molecules are removed upon heating and/or evacuation in order to generate coordinatively unsaturated metal sites. 23,34 The activated material has a characteristic honeycomb structure composed of 1D channels with abundant open metal sites. The open metal sites were found to be preferable for the adsorption of many gases in CPO-27: O 2 and N 2 in CPO-27-Fe, 26 CO 2 in CPO-27-Ni 35 and CPO-27-Mg, 19 CH 4 in CPO-27-Mg, 36 H 2 S molecule in CPO-27-Ni, [37][38] and C 2 H 2 in CPO-27-Co, 39 C 2 H 2 , C 2 H 4 , C 2 H 6 , C 3 H 6 , and C 3 H 8 in CPO-27-Fe.…”