Rigid and Flexible: A Highly Porous Metal–Organic Framework with Unusual Guest‐Dependent Dynamic Behavior

Abstract

Porous metal-organic materials [1] have attracted considerable attention in recent years because of their potential applications in many areas including gas storage, [2] separation, [3] and catalysis. [4] Because high framework stability is essential for many practical applications, the quest for metal-organic materials with rigid frameworks has been a subject of intense research. Since the first reports of metal-organic frameworks with permanent porosity, [5] many metal-organic frameworks have been reported to have stable porous structures; however, only a handful of these materials have a high surface area, [6] which is another important virtue of this class of materials. There is also growing interest in metal-organic materials with flexible and dynamic frameworks, [7] in particular, those that reversibly change their structures and properties in response to external stimuli as they may find applications, for example, in sensors.[8] However, porous materials that have both high framework stability and framework flexibility are rare.[9] Herein we report a novel metalorganic framework with permanent porosity and a high surface area, which also shows unusual guest-dependent dynamic behavior: the framework shrinks upon guest inclusion and expands upon guest release as proved unequivocally by single-crystal X-ray crystallography. These changes are fully reversible and depend on the nature of guests.Heating [10] The structure of 1·4 DMF· 1 = 2 H 2 O was determined by single-crystal X-ray diffraction and the phase purity of the bulk material was independently confirmed by powder X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and elemental analysis. The framework in 1·4 DMF· 1 = 2 H 2 O is composed of dinuclear Zn 2 units with a paddle wheel structure, which are bridged by 1,4-bdc dianions to form a distorted 2D square-grid {Zn 2 (1,4-bdc) 2 }. The axial sites of the Zn 2 paddle wheels are occupied by dabco, which act as pillars to extend the 2D layers into a 3D structure (Scheme 1). The overall topology of the framework in 1·4 DMF· 1 = 2 H 2 O is best described as a compressed primitive cubic (a-Po) net (Figure 1 a). The dabco pillars are disordered along the Scheme 1. The extension of the 2D square-grid of {Zn 2 (1,4-bdc) 2 } into a 3D structure by using dabco, which occupies the axial positions.

Modeling adsorption equilibria of xylene isomers in a microporous metal–organic framework

“…There exist two types of intersecting channels of about 7.5 Â 7.5 Å along the a-axis and channels of 3.8 Â 4.7 Å along b and c axes, respectively ( Fig. 1) [39].…”

Density functional calculations reveal a flexible version of the copper paddlewheel unit: implications for metal organic frameworks

“…An early example of such flexible MOFs was [Zn(bdc)2(dabco)]n (bdc = 1,4-benzenedicarboxylate; dabco = 1,4-diazabicyclo(2.2.2) octane) which contains layers of four-bladed paddle-wheel {Zn2(O2CR)4} units connected by dabco pillars. 3 The unit cell of this material is sensitive to adsorbed species ( Figure 1). The paddle-wheel motif ( Figure 2) is common in flexible MOFs with many zinc and copper examples.…”

Separation and Molecular-Level Segregation of Complex Alkane Mixtures in Metal−Organic Frameworks

“…In this work we refer to this structure, synthesized by Dybtsev et al, 8 as MOF-1. Figure 1 shows a cartoon of the structure.…”

“…6 Interestingly, recently Barcia et al found experimentally that hexane could be kinetically separated from 3-methylpentane and 2,2-dimethylbutane by fixed bed adsorption using a Zn 2 (1,4-bdc) 2 (dabco)] MOF, 7 where "bdc" denotes 1,4-benzenedicarboxylate and "dabco" denotes 1,4-diazabicyclo[2.2.2]-octane. In this work we refer to this structure, synthesized by Dybtsev et al, 8 as MOF-1. Figure 1 shows a cartoon of the structure.…”

“…MOF-1 is thermally stable and easily reactivated and reused. 8 To investigate the use of MOF-1 as an adsorbent for alkane separations relevant to industrial processes, we simulated a multicomponent mixture in the C 5 -C 7 range using grand canonical Monte Carlo (GCMC). Details are given in the Supporting Information.…”