Exceptional chemical and thermal stability of zeolitic imidazolate frameworks

Abstract

Twelve zeolitic imidazolate frameworks (ZIFs; termed ZIF-1 to -12) have been synthesized as crystals by copolymerization of either Zn(II) (ZIF-1 to -4, -6 to -8, and -10 to -11) or Co(II) (ZIF-9 and -12) with imidazolate-type links. The ZIF crystal structures are based on the nets of seven distinct aluminosilicate zeolites: tetrahedral Si(Al) and the bridging O are replaced with transition metal ion and imidazolate link, respectively. In addition, one example of mixed-coordination imidazolate of Zn(II) and In(III) (ZIF-5) based on the garnet net is reported. Study of the gas adsorption and thermal and chemical stability of two prototypical members, ZIF-8 and -11, demonstrated their permanent porosity (Langmuir surface area ‫؍‬ 1,810 m 2 ͞g), high thermal stability (up to 550°C), and remarkable chemical resistance to boiling alkaline water and organic solvents.catalysis ͉ hydrogen storage ͉ metal-organic frameworks ͉ porosity ͉ zeolites A large segment of the global economy ($350 billion) is based on the use of crystalline microporous zeolites in petrochemical cracking, ion-exchange for water softening and purification, and in the separation of gases (1). Zeolite structures are composed of tetrahedral Si(Al)O 4 units covalently joined by bridging O atoms to produce Ͼ150 different types of framework (2). A long-standing challenge is to incorporate transition metal ions and organic units within their pores and, more desirably, to do so as an integral part of the zeolite framework. This ability would be useful in many catalytic applications because the pores would be lined with a high concentration of ordered transition metal sites whose electronic and steric properties can be tailored by functionalization of the organic links. However, the vision of achieving such a zeolite that combines these features remains largely unrealized. Here, we outline a general synthesis of structures having zeolite framework topologies in which all tetrahedral atoms are transition metals, and all bridging ones are imidazolate (IM) units.Imidazole can lose a proton to form IM, 1. In examining the dense-phases Co(IM) 2 and Zn(IM) 2 , whose structures are based on nets of linked CoN 4 or ZnN 4 tetrahedra (3, 4), we noticed that IM bridges make an M-IM-M angle, 1, close to 145°, which is coincident with the Si-O-Si angle, 2, which is preferred and commonly found in many zeolites (see Scheme 1). We believed that it should be possible under the right conditions to prepare metal IMs adopting open-framework zeolite structures. Indeed, a number of relatively new Fe(II) (5), Co(II) (6, 7), Cu(II) (8), and Zn(II) (9) IM compounds have structures that are based on zeolite-like tetrahedral nets. However, these materials are relatively dense (nonporous) and͞or low-symmetry structures. Only very recently, Zn(II) IMs having symmetrical porous structures analogous to zeolites were reported (10). Two of the aforementioned compounds are included, as zeolitic IM framework (ZIF)-7 and -8, among the library of ZIFs we report here (Fig. 1).** The focus of th...

Tuning the magneto-structural properties of non-porous coordination polymers by HCl chemisorption

“…2), which is a racemic mixture. Fully deprotonated [pyim] − ligands connect adjacent Cu centres via the imidazolate moieties within the ligands, forming a Cu-NCN-Cu bridge, which is reminiscent of that found in the recently discovered zeolitic imidazolate frameworks 27,28 and that has been exploited to promote magnetic interactions in Cu II dimers 29 . The ligand pyimH has been previously used in the synthesis of mononuclear spin-crossover complexes acting as a bidentate ligand 30 , but its deprotonation to act as a tridentate ligand for the formation of a coordination polymer is unprecedented.…”

High capacity hydrogenstorage materials: attributes for automotive applications and techniques for materials discovery

“…metal clusters and organic linkers), relatively simple synthesis and characterization, and recent progress in increasing surface areas (as high as 5500 m 2 /g), 54 MOFs have become an alluring research topic. [55][56][57] This building block approach to solidstate chemistry has also incited the creation of other new families of similar highly porous, crystalline materials such as zeolitic imidazolate frameworks (ZIFs) 58 and covalent organic frameworks (COFs). 59 Both carbon-and MOF-based sorbents are attractive materials for hydrogen storage, as they have the potential to be low cost, are lightweight (translating to favorable gravimetric capacity), reversible, and possess facile hydrogen discharge (charge) kinetics.…”

Hydrogen Storage in a Prototypical Zeolitic Imidazolate Framework-8

“…At the same time, they possess the exceptional chemical stability and rich structural diversity of zeolites. 2 Because of these combined features, ZIFs show great promise for hydrogen storage applications. However, in contrast to a large number of extensive studies for other MOFs, [3][4][5] no experimental data concerning the nature of H 2 -ZIF interactions and the manner in which hydrogen molecules are adsorbed have been reported yet.…”

“…2 The high-resolution neutron diffraction data also enabled us to unambiguously determine the orientation (i.e., the hydrogen positions) of the methyl group, which was not possible in the X-ray measurement. We note that the methyl group orientation and associated tunnel-splitting is a very sensitive probe for determination of the guest-host interactions.…”