We are developing the science of building chemical structures from molecular building blocks; a field we refer to as Reticular Chemistry. It is concerned with linking of molecular building blocks (organic molecules, inorganic clusters, dendrimers, peptides, proteins,...) into predetermined structures in which such units are repeated and are held together by strong bonds. This research has led to the discovery of several classes of porous crystalline materials: metal-organic frameworks, covalent organic frameworks, and zeolitic imidazolate frameworks (MOFs, COFs, and ZIFs). In practice, this kind of chemistry requires a multi-disciplinary approach involving inorganic synthesis of metal complexes and frameworks, organic synthesis of the linkers and synthetic modification of frameworks' interior, solid-state and solution synthesis, and the characterization techniques associated with these diverse areas ranging from electron microscopy, NMR, X-ray crystallography, neutron diffraction to gas adsorption isotherm measurements. We design open frameworks to have ultrahigh porosity (up to 6,000-10,000 meter square per gram) exceeding traditional porous materials such as zeolites, mesoporous silica and carbon; making MOFs, COFs and ZIFs useful for clean energy storage and generation.
Presently, we are able to design the structure of the frameworks, their functionality, and the pore environment and metrics to produce crystalline materials capable of storage and separation of hydrogen, methane, carbon dioxide, water, volatile organics, peptides and proteins. The ability to functionalize the interior of the pores also results in enzyme-like active sites installed within the confines of such MOF structures for their use in catalysis of reactions leading to clean energy generation: conversion of methane to methanol, water to hydrogen and oxygen, organic cyclization reactions, and carbon-carbon bond breaking reactions.
We have also made progress in transferring this precise control in building frameworks to the design of nano-MOFs and the development of their use as supercapacitors, proton and electron conductive materials. We continue to extend this chemistry to new frameworks and nanocrystals in which the pores are decorated by multiple functionalities arranged and apportioned in unique sequences throughout the material. We believe these regions and sequences code for specific properties in a way that is not too dissimilar from sequences of nucleotides in DNA and amino acids in proteins. Thus our work is aimed at making MOF, COF and ZIF materials capable of (a) counting and sorting molecules, (b) having compartments which are linked yet function synergistically, (c) carrying out multiple catalytic transformations in precisely controlled molecular space, and (d) exhibiting hybrid properties of molecular recognition, signal transduction and mechanical action.
Recently, we have succeeded in demonstrating the use of MOFs to harvest water from the desert air, as well as pioneered molecular weaving. We used coordination chemistry to bring together organic threads in a weaving manner. Once the structure is formed, it can be demetalated leaving behind a thoroughly woven organic ‘cloth’ for which the elastic properties are dramatically different than those of the metalaled forms. Molecularly woven chemical structures of this kind provide means of accessing frameworks that combine dynamics with resiliency. The principles of this new science are being extended to polymers and nanocrystals.
In the News
Omar Yaghi, one of the world’s most cited chemists and leading authorities on nanoscience, is the new director of the Molecular Foundry, a U.S. Department of Energy nanoscience center at Berkeley Lab.