Secondary Construction Units (SBU) – the turning point in the development of organometallic structures (MOFs)

The last two decades have seen explosive growth in the MOF field, with more than 84,185 MOF structures documented in the Cambridge Crystallographic Data Center. A collection of articles on the synthesis, structure and application of MOFs continues to be published each year. The SBU approach has made MOF chemistry the main contributor to the rapid development observed in the field. Many syntheses, surveys and MOF applications are derived from the SBU approach. We now go over the field of MOF chemistry for Progress of science, Markus Kalmutzki, Nikita Hankel and Omar M. Yaghi – recently received the BBVA Foundation Award for Knowledge Frontiers in the Basic Science category – and discuss the history of MOFs and their applications under the SBU approach .

Organometallic structures (MOFs) are a fascinating class of highly porous materials. They are structurally composed of ions / clusters of metals and organic linkers for promising functional diversity in various fields. Properties include their unique crystallinity, adjustable porosity and structural diversity. The performance of MOFs has been demonstrated in various applications such as gas storage, catalysis detection and drug delivery. In particular, SBUs play an important role in vapor absorption, as indicated with high water absorption. The structural diversity of MOFs depends on SBU. Future work is planned for industrial applications, including absorption and separation of gases, recovery of water in the air, bio-imaging and therapeutics.

By design, polynuclear cluster nodes, also called SBUs, are capable of conferring (1) thermodynamic stability via strong covalent bonds and (2) mechanical / architectural stability through strong directional bonds that can lock the centers' position. metallic in the metal-organic. frames. This property contrasts with unstable and non-directional single metal nodes that formed weak bonds with neutral organic donor linkers.

Unlike the unpredictable method of traditional synthetic organic chemistry, in which there is little or no correlation between the structure of starting materials and products, MOF chemistry offers greater predictability because they are designed with predetermined topologies. In the synthesis process, the chemical building units required to build the selected network are determined. The structural diversity observed in MOF chemistry stems from a wide variety of available SBU geometries; specific structures can be designed by choosing building units of appropriate shape and size.

The authors then detailed various MOF synthesis methods, their complexity, their chemical frameworks, and their applications, derived from secondary construction units during MOF development. In practice, MOFs can be used for gas storage and separation, with specific implications for separating carbon dioxide and other greenhouse gases for environmental sustainability. Metal organic structures can also form polyvalent heterogeneous catalysts for efficient organic transformations, be used as luminescent sensors and in the distribution of drug cargoes for the treatment of cancer.

Applications in various fields have been made possible by the porosity inherent in MOFs, made possible by the SBU approach. The chemical nature inherent in the MOFs and SBUs that led to the development of the adsorption, separation and catalysis properties was then dissected as part of the review. The accessibility of pore space within open framework structures allowed the observed application for MOFs in different areas. The basis of MOFs is related to the ability to manipulate matter with a precision known until now only in well-established molecular chemistry.

The crystallinity and porosity of the structure were fully preserved during construction, which led to the development of "crystals as molecules". The introduction of the SBU approach has been a turning point in extending the precision chemistry of molecular complexes and polymers to two-dimensional and three-dimensional structures, in order to design rational structures using functional construction units. Recent progress in the field of MOF synthesis confirms the translation potential of functional building unit properties into a structural framework. These properties include linear and nonlinear optical character, magnetism, conductivity and catalysis. Recent advances in computer chemistry can also help to understand the properties of materials and predict the structures that can be constructed with the targeted character.

Complexity and heterogeneity can be incorporated into the recently proposed MOFs, in order to explore and analyze their impact on the resulting structure and properties in the future. Complexity and heterogeneity allow both to expand the scope of structures and to provide access to materials with high potential for increased performance. Controlling the spatial distribution of different organic functionalities and metal ions can lead to design sequences in or along the MOF skeleton. Expected spatial arrangements can be achieved by integrating several SBUs with specific binding patterns directly into the formation of the single-material structure, or via post-synthetic methods. Achieving this vision can result in sequence-specific materials designed in the MOFs to perform the intended functions. The introduction of SBU marks a turning point in the development of MOF chemistry – and will continue to play a key role in their future development to access new structures, properties and applications.

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More information:
Markus J. Kalmutzki et al. Secondary building units are the turning point in the development of the reticular chemistry of MOFs, Progress of science (2018). DOI: 10.1126 / sciadv.aat9180