Reticular materials are artificial materials that have been engineered at the molecular level to achieve certain properties, in particular a high porosity and high surface area. Reticular materials can be grouped into three major classes, in the order of their discovery: metal-organic frameworks or MOFs, covalent organic frameworks or COFs, and hydrogen-bonded organic frameworks or HOFs, each with respective sub-classes. An example for a sub-class of MOFs are zeolitic Imidazolate Frameworks (ZIFs).
MOFs are the most explored sub-class of reticular materials (around 77% of the approximately 48,000 publications on reticular materials between the 1990s to 2023 were on MOFs). MOFs are a type (or subclass) of coordination polymers. Around 99 thousand synthetic variants of MOF are known. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License The structures and functionality of reticular materials, for example the pore size, are adjustable (or “tailorable”) during the synthesis process. This makes them in principle adjustable to many different technical requirements. Depending on the choice of materials and synthesis methods, reticular materials, because of the strong bonds, can be designed to withstand extreme temperatures and harsh chemical environments over extended periods of time. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
This field was pioneered by Susumu Kitagawa, Richard Robson, and Omar M. Yaghi starting in the 1990s. These three scientists received the Nobel Prize in Chemistry in 2025 “for the development of metal–organic frameworks”.
There are many potential applications for reticular materials, although only very few applications have reached a commercial level to date. The initial application of reticular materials was mostly for gas adsorption and storage, followed later by other fields such as catalysis, biomedicine, and membrane technologies. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License Examples for gas adsorption and storage technologies with reticular materials include carbon capture and storage, direct air capture, atmospheric water harvesting and hydrogen storage. These are all applications that several start-up or commercial companies are now pursuing. Other applications that are being researched, including for biomedicine and catalysis, are still in their infancy and emerging states. Research is ongoing around the world to take the most promising reticular materials into the full-scale commercialization process for real-world applications. Hindering factors include scalability, high costs of reticular materials, reproducibility and poor technology readiness level. The company BASF produces raw MOFs at commercial quantities. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
Definition and overview Reticular materials are materials that are constructed based on the concept of reticular chemistry. The term reticular is derived from the Latin term reticulum meaning net-like. The first-discovered and largest class of reticular materials are metal–organic frameworks (MOFs) but there are other classes, too, as well as many sub-classes. The two main other classes of reticular materials are covalent organic framework (COFs) and hydrogen-bonded organic framework (HOFs).
Reticular chemistry involves the “connection of individual building units such as molecules and clusters using robust bonding to form extensive and coherent architectures with highly ordered arrangement in a designed manner”. In other words, reticular chemistry is “concerned with linking molecular building units by strong bonds to make crystalline large and extended structures”. The term reticular synthesis, or reticular chemistry was introduced in 2002–2003 by the research team at UC Berkeley led by Omar M. Yaghi.
This emerging field of reticular chemistry has at its core inorganic and organic chemistry but it also adds the new chemistry of using the strong metal-ion-based bonds and covalent bonds to link molecules into extended structures, features unattainable prior to reticular chemistry. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
Prior to the discovery of MOFs, zeolites and activated carbons were the main porous materials used in industry for applications where a high surface area was required. However, the surface area of MOFs is much higher than that of zeolites and activated carbons, i.e. in the range of 1000–10,000 m2/g. This makes them an interesting material for industry.
In addition, the structure of the cavities and the size of the pore in MOFs can be tailored as a function of metal ions, organic ligands, and synthesis conditions, and hence are thus amenable to engineering for targeted applications.
History
In the 1990s, the research activities of Omar M. Yaghi first at the Arizona State University and then at University of Michigan in the United States involved synthesizing ordered molecular structures. In 1999 he and co-authors published an article in Nature called “Design and synthesis of an exceptionally stable and highly porous metal-organic framework” where they described MOF-5, the first MOF to exhibit ultra-high porosity. This marked the beginning of a new research field. The new term metal–organic framework was coined by that research group. The evolution of porous materials with diverse topologies has a rich history, traced back to the assembly of inorganic clusters into extended frameworks. This was followed by the synthesis of metal–organic frameworks (MOFs) in the 1990s, which involved linking organic molecules and metal ions. Subsequently, covalent organic frameworks (COFs) emerged after first being synthesized by Omar M. Yaghi and his group in 2005. COFs are a type of reticular material that links organic molecules together. This was later followed by hydrogen-bonded organic frameworks (HOFs) (since around 2011), representing the latest generation of reticular materials. A publication in 2011 by Banglin Chen (University of Texas at San Antonio) introduced the term HOF to the scientific community.Almost 48 000 publications on reticular materials have been published in the three decades between the 1990s and 2023. Of these publications, most of them (around 77%) are on MOFs. They are the most explored sub-class of reticular materials.
Reticular materials are now (as of 2022) the “fastest-growing class of materials in chemistry and most-productive research hotspot among global communities of chemistry, engineering, and materials science.”
The scientists Omar M. Yaghi, Susumu Kitagawa and Richard Robson received the Nobel Prize in Chemistry in 2025 “for the development of metal–organic frameworks”. They have pioneered the field of reticular materials and chemistry.
Terminology There are many other terms that are related to reticular materials in the scientific literature, making it confusing for non-experts, as some terms are synonyms, some are “historical”, whereas others describe sub-classes or overarching terms. Also in some cases, different research groups use different terminology.
Some publications use the term MOF informally like a synonym of reticular materials, so that MOF would include COF and HOF as well. However, this is imprecise usage and a linguistic simplification.
Adding to the confusion is that compounds with metal ions bound by organic linkers have been “differently named: metal-organic frameworks, coordination polymers, metal-organic polymers, hybrid organic-inorganic materials and organic zeolite analogues”.
It was Yaghi's group at the university UC Berkeley that bestowed these materials with a distinctive naming convention, highlighting their contribution to the field. In 2006, the same group proposed the systematic name of zeolitic imidazolate frameworks, abbreviated as ZIF.
The IUPAC Recommendations from 2013 recommended a hierarchical terminology as follows “the most general term is coordination polymer. Coordination networks are a subset of coordination polymers and MOFs a further subset of coordination networks”. Therefore, MOFs are a type (or subclass) of coordination polymers.
The term porous polymer is also used as an overarching term for MOFs, COFs and HOFs.
With regards to sub-classes of reticular materials: Porous organic frameworks (POFs) are a sub-class of reticular materials and thought to be among the most significant categories of reticular materials. Reticular framework nanoparticles (RFNPs) are also a sub-class of reticular materials.
Classes
Classification systems Reticular materials can be grouped into three major classes: metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and hydrogen-bonded organic frameworks (HOFs), each with respective sub-classes:
Metal-organic frameworks (MOFs) (with a range of sub-classes for example Cyclodextrin-metal–organic framework (CD-MOF), Zeolitic Imidazolate Frameworks (ZIFs), Carboxylate-based metal–organic frameworks, Conductive metal−organic frameworks)
Covalent organic frameworks (COFs)
Hydrogen-bonded organic frameworks (HOFs)
Metal-organic framework (MOF) The first reticular framework was synthesized in 1995, when it was discovered that metal ions could be bound to charged bonding agents, such as carboxylates, leading to the formation of crystalline 2D structures. A major breakthrough was achieved by linking inorganic clustered secondary building units (SBUs) with shape-defining connectors using strong molecular bonds.
Metal–organic frameworks (MOFs) are porous materials made from metal ions or clusters (also called joints) connected by organic ligands (linkers). These components combine to form structural units known as secondary building units (SBUs). A wide range of metal ions can be used, including transition metals, lanthanides, alkali metals and many others. Also the organic linkers can contain many different functional groups such as carboxylate, phosphonate, sulfonate, pyridyl, imidazolate.
During the initial stages of their development, the primary objective was centered on synthesizing new MOF structures. However, as the field progressed, there was a gradual transition toward studying the performance and applications of MOFs, which gained momentum with the emergence of stable MOFs like UiO, MIL, and ZIF.
To indicate a specific MOF, different naming methods are used: One way is to write MOF followed by a number, e.g. MOF-5. Another option is to include the location of the research group (like UiOs for University of Oslo, NU for Northwestern University, or HKUST for Hong Kong University of Science and Technology or LIC for Leiden Institute of Chemistry) or the name of the research team (like CPL, F-MOF-1, and MOP-1).
MOF crystal size can be controlled at the nanometre level to build MOF nanoparticles (abbreviated as MOF NPs). Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
The zeolite imidazolate frameworks (ZIFs) are a type of MOF and consist of many different materials. They all share a similar structure: transition metals such as zinc, iron, copper, or cobalt are connected by nitrogen atoms and linked together by imidazole rings.
A selection of notable MOFs, their key characteristics and applications. These MOFs are notable based on the timing of their discovery (e.g. being the first one) or because of full scale applications. Name Key characteristics Possible applications (mostly laboratory; few large-scale) Source MOF-5 One of the earliest MOFs discovered (research published in 1999)
Composed of zinc oxide (Zn4O) clusters and terephthalic acid (BDC) ligands