Impact of Defects on Pyrazolate Based Metal Organic Frameworks

Abstract

The high strength of the metal-pyrazolate coordination bond allows the deliberate introduction of defects on pyrazolate based metal-organic frameworks without affecting the integrity of the porous crystalline network. Yet the presence of defects has a major impact on the properties of these systems which include higher pore accessibility and increased interactions with guest molecules, higher ion/ electronic mobility and enhanced catalytic properties. In this review selected examples of the impact of the presence of defects in the capture of environmentally relevant gases, ion and electronic conductivity and catalytic properties of defective pyrazolate based metal organic frameworks are given.

Diffusion Control in Single-Site Zinc Reticular Amination Catalysts

“…The ZnBDP shows a higher uptake with respect to ZIF-8, resulting in 1.0 vs 0.3 mol Cl-py •mol Zn −1 (see Table S4 in the Supporting Information). A computational study has been performed with both reticular Zn catalysts (i.e., Zn 12 (C 4 N 2 H 5 ) 24 and Zn 4 (C 12 N 4 H 8 ) 4 modeled crystalline cells of ZIF-8 and ZnBDP, respectively) in order to understand the experimental results. The calculated values are in line with the experimental uptake of Cl-py molecules by the MOFs, corresponding to 0.4 and 1.0 mol Cl-py or morpholine •mol Zn −1 docked in ZIF-8 and ZnBDP, respectively.…”

“…This limitation might be more easily overcome by using earth abundant metalazolate frameworks based on extended linkers. [24][25][26][27][28] This family of robust MOFs have demonstrated catalytic activity in aldol condensations -Michael-type additions, 29 hydroaminations, 30 cross couplings, 31,32 and carboxylations. 33 Pyrazolate groups favor soft-soft acid-base interactions (with divalent metals) for higher thermal stability and exceptional chemical stability in acid and basic conditions, compared to carboxylate MOFs.…”

“…Pioneering studies of copper active sites in MOFs for N-arylations of aryl bromides with aromatic amines and N-heterocycles using Ullmann-type couplings have been reported. , However, the harsh conditions used, which include large amounts of base, compromises the stability and recyclability of the framework. This limitation might be more easily overcome by using earth abundant metal-azolate frameworks based on extended linkers. − This family of robust MOFs have demonstrated catalytic activity in aldol condensations–Michael-type additions, hydroaminations, cross-couplings, , and carboxylations . Pyrazolate groups favor soft–soft acid–base interactions (with divalent metals) for higher thermal stability and exceptional chemical stability in acid and basic conditions, compared to carboxylate MOFs .…”

Design of Hierarchical Architectures in Metal–Oganic Frameworks for Catalysis and Adsorption

“…These unique soft–soft acid–base interactions also allow the generation of new isoreticular MOF series with tunable organic functionalities and pore sizes. This, in principle, could overcome benchmark uptake capacities, molecular diffusions, and adsorption selectivity to a guest molecule . For example, −NH 2 , −NO 2 , −SO 3 , and −OH containing ZnBDP azolate-type MOFs have been prepared in the form of straight chains of tetrahedrally coordinated Zn­(II) ions in a square-lattice topology (entry 22 in Table ).…”

Vacancies in Metal−Organic Frameworks: Formation, Arrangement, and Functions

“…Vacancies endow MOFs with new properties that are not intrinsic to their defect-free counterparts, and the concept of "defect engineering" for structure modification and functionalization has been extensively explored and reviewed. [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] In this review, we would like to limit our scope of MOF functions to three important aspects, in which the interaction mechanism between the guests and the vacancy sites is definite (Section 6). Specifically, vacancy sites serving as atomically precise positions for 1) gas adsorption and separation, 2) additional entity grafting for materials functionalization, and 3) highly efficient molecular conversion will be discussed (Figure 1g).…”