Zeolites are one of humanity's most important synthetic products. These aluminosilicate-based materials represent a large segment of the global economy. Indeed, the value of zeolites used in petroleum refining as catalysts and in detergents as water softeners is estimated at $350 billion per year. A major current goal in zeolite chemistry is to create a structure in which metal ions and functionalizable organic units make up an integral part of the framework. Such a structure, by virtue of the flexibility with which metal ions and organic moieties can be varied, is viewed as a key to further improving zeolite properties and accessing new applications. Recently, it was recognized that the Si-O-Si preferred angle in zeolites (145 degrees ) is coincident with that of the bridging angle in the M-Im-M fragment (where M is Zn or Co and Im is imidazolate), and therefore it should be possible to make new zeolitic imidazolate frameworks (ZIFs) with topologies based on those of tetrahedral zeolites. This idea was successful and proved to be quite fruitful; within the last 5 years over 90 new ZIF structures have been reported. The recent application of high-throughput synthesis and characterization of ZIFs has expanded this structure space significantly: it is now possible to make ZIFs with topologies previously unknown in zeolites, in addition to mimicking known structures. In this Account, we describe the general preparation of crystalline ZIFs, discussing the methods that have been developed to create and analyze the variety of materials afforded. We include a comprehensive list of all known ZIFs, including structure, topology, and pore metrics. We also examine how complexity might be introduced into new structures, highlighting how link-link interactions might be exploited to effect particular cage sizes, create polarity variations between pores, or adjust framework robustness, for example. The chemical and thermal stability of ZIFs permit many applications, such as the capture of CO(2) and its selective separation from industrially relevant gas mixtures. Currently, ZIFs are the best porous materials for the selective capture of CO(2); furthermore, they show exceptionally high capacity for CO(2) among adsorbents operating by physisorption. The stability of ZIFs has also enabled organic transformations to be carried out on the crystals, yielding covalently functionalized isoreticular structures wherein the topology, crystallinity, and porosity of the ZIF structure are maintained throughout the reaction process. These reactions, being carried out on macroscopic crystals that behave as single molecules, have enabled the realization of the chemist's dream of using "crystals as molecules", opening the way for the application of the extensive library of organic reactions to the functionalization of useful extended porous structures.

Enhancing the robustness of functional biomacromolecules is a critical challenge in biotechnology, which if addressed would enhance their use in pharmaceuticals, chemical processing and biostorage. Here we report a novel method, inspired by natural biomineralization processes, which provides unprecedented protection of biomacromolecules by encapsulating them within a class of porous materials termed metal-organic frameworks. We show that proteins, enzymes and DNA rapidly induce the formation of protective metal-organic framework coatings under physiological conditions by concentrating the framework building blocks and facilitating crystallization around the biomacromolecules. The resulting biocomposite is stable under conditions that would normally decompose many biological macromolecules. For example, urease and horseradish peroxidase protected within a metal-organic framework shell are found to retain bioactivity after being treated at 80 °C and boiled in dimethylformamide (153 °C), respectively. This rapid, low-cost biomimetic mineralization process gives rise to new possibilities for the exploitation of biomacromolecules.

We show that metal-organic frameworks (MOFs) can incorporate a large number of different functionalities on linking groups in a way that mixes the linker, rather than forming separate domains. We made complex MOFs from 1,4-benzenedicarboxylate (denoted by "A" in this work) and its derivatives -NH2, -Br, -(Cl)2, -NO2, -(CH3)2, -C4H4, -(OC3H5)2, and -(OC7H7)2 (denoted by "B" to "I," respectively) to synthesize 18 multivariate (MTV) MOF-5 type structures that contain up to eight distinct functionalities in one phase. The backbone (zinc oxide and phenylene units) of these structures is ordered, but the distribution of functional groups is disordered. The complex arrangements of several functional groups within the pores can lead to properties that are not simply linear sums of those of the pure components. For example, a member of this series, MTV-MOF-5-EHI, exhibits up to 400% better selectivity for carbon dioxide over carbon monoxide compared with its best same-link counterparts.

A new crystalline zeolitic imidazolate framework, ZIF-90, was prepared from zinc(II) nitrate and imidazolate-2-carboxyaldehyde (ICA) and found to have the sodalite-type topology. Its 3D porous framework has an aperture of 3.5 A and a pore size of 11.2 A. The pores are decorated by the aldehyde functionality of ICA which has allowed its transformation to the alcohol functionality by reduction with NaBH4 and its conversion to imine functionality by reaction with ethanolamine to give ZIF-91 and ZIF-92, respectively. The N2 adsorption isotherm of ZIF-90 shows a highly porous material with calculated Langmuir and BET surface areas of 1320 and 1270 m2 g(-1). Both functionalized ZIFs retained high crystallinity and in addition ZIF-91 maintained permanent porosity (surface areas: 1070 and 1010 m2 g(-1)).

Condensation of 2,5-diethoxyterephthalohydrazide with 1,3,5-triformylbenzene or 1,3,5-tris(4-formylphenyl)benzene yields two new covalent organic frameworks, COF-42 and COF-43, in which the organic building units are linked through hydrazone bonds to form extended two-dimensional porous frameworks. Both materials are highly crystalline, display excellent chemical and thermal stability, and are permanently porous. These new COFs expand the scope of possibilities for this emerging class of porous materials.

Covalent organic frameworks (COFs) are porous crystalline materials composed of light elements linked by strong covalent bonds. A number of these materials contain a high density of Lewis acid boron sites that can strongly interact with Lewis basic guests, which makes them ideal for the storage of corrosive chemicals such as ammonia. We found that a member of the covalent organic framework family, COF-10, shows the highest uptake capacity (15 mol kg⁻¹, 298 K, 1 bar) of any porous material, including microporous 13X zeolite (9 mol kg⁻¹), Amberlyst 15 (11 mol kg⁻¹) and mesoporous silica, MCM-41 (7.9 mol kg⁻¹). Notably, ammonia can be removed from the pores of COF-10 by heating samples at 200°C under vacuum. In addition, repeated adsorption of ammonia into COF-10 causes a shift in the interlayer packing, which reduces its apparent surface area to nitrogen. However, owing to the strong Lewis acid-base interactions, the total uptake capacity of ammonia and the structural integrity of the COF are maintained after several cycles of adsorption/desorption.

Encapsulation of biomacromolecules in metal− organic frameworks (MOFs) can preserve biological functionality in harsh environments. Despite the success of this approach, termed biomimietic mineralization, limited consideration has been given to the chemistry of the MOF coating. Here, we show that enzymes encapsulated within hydrophilic MAF-7 or ZIF-90 retain enzymatic activity upon encapsulation and when exposed to high temperatures, denaturing or proteolytic agents, and organic solvents, whereas hydrophobic ZIF-8 affords inactive catalase and negligible protection to urease.

Due to their efficiency, selectivity, and environmental sustainability, there are significant opportunities for enzymes in chemical synthesis and biotechnology. However, as the three-dimensional active structure of enzymes is predominantly maintained by weaker non-covalent interactions, thermal, pH and chemical stressors can modify or eliminate activity. Metal-organic Frameworks (MOFs), which are extended porous network materials assembled by a bottom-up building block approach from metal-based nodes and organic linkers, can be used to afford protection to enzymes. The self-assembled structures of MOFs can be used to encase an enzyme in a process called encapsulation when the MOF is synthesized in the presence of the biomolecule. Alternatively, enzymes can be infiltrated into mesoporous MOF structures or surface bound via covalent or non-covalent processes. Integration of MOF materials and enzymes in this way affords protection and allows the enzyme to maintain activity in challenge conditions (e.g. denaturing agents, elevated temperature, non-native pH and organic solvents). In addition to forming simple enzyme/MOF biocomposites, other materials can be introduced to the composites to improve recovery or facilitate advanced applications in sensing and fuel cell technology. This review canvasses enzyme protection via encapsulation, pore infiltration and surface adsorption and summarizes strategies to form multi-component composites. Also, given that enzyme/MOF biocomposites straddle materials chemistry and enzymology, this review provides an assessment of the characterization methodologies used for MOF-immobilized enzymes and identifies some key parameters to facilitate development of the field. CONTENTSMOF-based enzyme biocomposite compositions and the concept of encapsulation 3.MOF-based enzyme biocomposites formed via encapsulation 3.1.Templating methods 3.2.One-pot embedding (non-templated) 3.3.Parameters influencing the chemistry of enzyme@MOF biocomposites 3.3.1. Additives 3.3.2.Enzyme suface chemistry 3.3.3.MOF precusors and structures 3.4.Alternative synthesis strategies 4.Infiltration (post insertion of enzymes in preformed MOFs) 4.1.Early results and the advantages of MOFs for infiltration 4.2.Tuning the framework structure in infiltrated enzyme@MOF biocomposites 4.3.Towards applications of infiltrated enzyme@MOFs 5.Surface bound enzymes 5.1. Immobilization via physical adsorption 5.2. Immobilization via coordinate bonds 5.3. Immobilization via covalent bonding 5.4. Enzymatic activity upon surface-immobilization 6. Multicomponent biocomposites 7. Characterization of MOF immobilized enzymes 7.1. Overview 7.2. Key immobilization parameters 7.3. One-pot enzyme MOF formation 7.4. Highlights of MOF-immobilized enzyme performance 7.4.1. Experimental determination of key immobilization parameters 7.4.1.1. Determination of protein concentrations 7.4.1.2. Activity determination 7.4.2. Advanced characterization of immobilized enzymes 7.4.2.1. Apparent enzyme kinetics 7.4.2.2. Structural analysis and localization o...