Jeffrey R. Long

Inorganic and materials chemistry; synthesis of inorganic molecules and higher dimensional solids; precise tailoring of chemical and physical properties; gas storage, molecular separations, and catalysis in porous materials; magnetic and conductive materials.

Description

Research in the Long group focuses on the design and controlled synthesis of novel inorganic materials and molecules toward the fundamental understanding of new physical phenomena, with applications in gas storage, molecular separations, conductivity, catalysis, and magnetism. We employ a range of physical methods to analyze and characterize our materials comprehensively, including by gas adsorption analysis, X-ray and neutron diffraction, various spectroscopic techniques, and SQUID magnetometry. For more information about the Long group and a full list of publications, please visit the group website.

Metal–Organic Frameworks

A major focus of research in the Long group is the design and study of metal–organic frameworks—porous, inorganic solids built of metal nodes connected by organic linkers—that are of interest for applications ranging from gas storage and molecular separations to catalysis and battery applications.

Industrial separations account for a staggering 10-15% of the total global energy consumption, and developing more efficient separations processes is a therefore key strategy toward reducing worldwide energy consumption. Additionally, now more than ever global warming is necessitating a dramatic reduction in our global greenhouse emissions. One of the most promising short-term emissions mitigation strategies—and therefore a crucial separations need—is the removal of CO₂ directly from the flue gas streams of coal- and natural gas-fired power plants. Toward this end, we are studying a new class of diamine-appended frameworks developed in our group that exhibit high CO₂ separation capacities in the presence of water, with minimal energy requirements arising from an unprecedented cooperative adsorption mechanism. Beyond terrestrial separations technologies, we are seeking to optimize this cooperative mechanism for applications as far reaching as air purification in submarines and spacecraft, and are applying fundamental insights from this work to the design of novel materials and mechanisms for the cooperative adsorption of other key, industrially-relevant gas molecules.

We are also targeting metal–organic frameworks featuring polarizing open metal sites and shape-discriminating pore structures for the enhanced binding of H₂ and CH₄ near ambient temperatures and the separation of hydrocarbon isomers, respectively. The high-capacity storage of hydrogen and natural gas is especially relevant for automotive transportation, as these gases represent promising cleaner alternatives to liquid hydrocarbon fuels, and yet major advances in adsorbent technologies are necessary to overcome the costly limitations currently imposed by low-temperature and high-pressure on-board storage requirements. Seeking to capitalize on the separation capabilities of our best performing framework materials and the robust nature of polymer membranes, we are also designing metal–organic framework/polymer composites toward the development of novel membranes that exhibit high selectivities and permeabilities for applications ranging from the purification of natural gas to olefin/paraffin separations.

Catalysis and Conductivity

In addition to their function as molecular sieves, metal–organic frameworks are promising as robust, efficient catalysts with isolated and well-defined active sites. We are seeking to use coordinatively-unsaturated framework metal centers as catalytic sites and also installing these metal centers post-synthetically via chelating groups built into the framework ligands. In a separate endeavor, we are using this post-synthetic modification strategy to reduce or oxidize insulating frameworks and target conductive materials with high charge densities for applications ranging from battery components to chemical sensors. Along with their unique electronic properties, we are discovering unprecedented magnetic phenomena in some of these materials, and thus these efforts represent new directions in fundamental materials science.

Molecular Magnetism

Research in the Long group is also heavily focused on the design of molecules exhibiting a strong directional dependence to their magnetization (known as magnetic anisotropy) and magnetic phenomena such as magnetic hysteresis, a property previously thought to be relegated to bulk magnetic materials. These compounds—collectively known as single-molecule magnets—were discovered in the early 20^th century and are of interest for applications in information storage, spin-based electronics, and quantum computing. Nearly thirty years after their discovery, however, the highest performing single-molecule magnets still only exhibit operating temperatures as high as ~60 K, with the vast majority only functioning at temperatures of a few K—as cold as deep space. At higher temperatures, thermal energy causes random fluctuations of the molecular magnetization that precludes the controlled manipulation of spin that is necessary for practical applications.

The Long group is employing new design motifs and architectures precisely chosen to enhance operating temperatures, focusing primarily on the synthesis of multinuclear, radical-bridged molecules incorporating the late trivalent lanthanides and low-coordinate, mononuclear complexes of the transition metals. In particular, the trivalent lanthanides possess large magnetic moments and unquenched orbital angular momentum that can give rise to large magnetic anisotropy when paired with the appropriate ligand environment, and the group is a foremost leader in the design of high-performing, radical-bridged lanthanide single-molecule magnets.

While the lanthanide ions are unsurpassed in their physical properties and the fundamental advantages they bring to the design of single-molecule magnets, the increasing costs associated with lanthanide extraction are also spurring interest in the development of molecules incorporating the less costly and abundant transition metals as magnetic centers. Transition metals led the charge with the development of single-molecule magnets, as magnetic centers in large, multinuclear clusters, and the group is now targeting mononuclear transition metal complexes of iron and cobalt that exhibit “lanthanide-like” electronic structure imparted by the appropriate weak, low-coordinate ligand field. The group is also pursuing new avenues in the design of multinuclear transition metal compounds with large spin and magnetic anisotropy, as well as mononuclear and multinuclear complexes of the 5f-elements.