This page highlights some current areas of research of our group. While this list is far from comprehensive, we hope it gives the reader an overview of the many types of projects and approaches our group develops. Our lab is primarily focused on the use and development of two solid-state techniques: mechanochemical milling, and accelerated ageing.
Neat and Liquid Assisted Grinding
For Neat Grinding, solid reactants are placed in a stainless steel jar with stainless steel balls and milled at 30Hz in a Retsch® MM400 mill for varying amounts of time. Liquid Assisted Grinding follows the same procedure but a small amount of liquid (20 to 200μL) is added in order to increase reactivity. In the ILAG variant, a catalytic amount of an ionic salt is added (often ammonium species) along with liquid to the otherwise solid reactants.
Accelerated Ageing which operates by first mixing our reactants in our ball mill for a short amount of time, and subsequently exposing these homogenized but unreacted samples to humidity (varies from 70% to 100% depending on the climate chamber). Quantitative conversions have been observed within hours but generally take a few days to weeks.
MOFs and ZIFS
One of the most prominent research areas of our group are Metal Organic Frameworks. Our focus has largely been on developing new cost-effective and environmentally benign syntheses of MOFs and Zeolitic Imidizolate Frameworks using mechanochemistry and our novel "accelerated ageing" technique. One of our first papers on accelerated ageing describes the synthesis of ZIF-8 a highly porous MOF. We have also synthesized a new class of imidazolium frameworks where imidazolium ions bridge anions to create hydrogen bonded frameworks analagous to ZIFs. Additionally, we examine the properties of these materials in regards to their stability towards carbon dioxide.
We are currently developing large scale sustainable syntheses of MOFs with interesting properties such as MOF-74 and UiO-66. Our interest in MOFs is not limited to synthetic methodologies and we are synthesizing new MOFs, including the rare organic minerals stepanovite and zhemchuzhnikovite which are porous magnetic and proton conducting metal oxalate MOFs. We continue to synthesize a wide variety of MOF materials and explore their properties for gas storage, catalysis, and fluorescence.
In Situ Monitoring of Mechanochemical Reactions
Towards this goal,in collaboration with an international research team at the European Synchrotron Radiation Facility, we have pioneered the in-situ monitoring of mechanochemical reactions in order to better elucidate mechanisms involved in the mechanochemical synthesis of ZIFs and MOFs, pharmaceutical cocrystals, and other milling reactions. This work has been highlighted by Nature and represents the most comprehensive mechanistic examination of milling reactions to date. These techniques have enabled us to make ground-breaking discoveries, such a ZIF framework with a previously unknown topology.
Thermodynamic Stabilities of MOFs
In collaboration with Dr. Alexandra Navrotsky's group at UC Davis, we have combined solution calorimetry and periodic DFT to analyze the thermodynamics of two families of topologically distinct polymorphs of zinc zeolitic imidazolate frameworks (ZIFs) based on 2-methyl- and 2-ethylimidazolate linkers. These results demonstrate a correlation between density and thermodynamic stability, and allow us to probe the effects of ligand substituion. These results suggest that mechanochemical synthesis of ZIFs proceeds through thermodynamically increasingly stable and more dense phases.
Solvent Free Metal Separation
Everyday we use and utilise objects with metal parts, however, most metals, do not come as pure substances but have to be obtained from their mixed ores; mostly oxides, silicates and sulfides. This separation and purification is costly and requires the use of hot, concentrated acids and industrial solvents and huge amounts of water. All this puts an immense strain on our environment. It is our aim to develop solvent-free, solid-state separation of metals from ore-like matrices using cheap and ecologicaly friendly organic ligands. The reactions are facilitated by mechanochemical grinding and accelerated ageing at room, or slightly elevated temperatures. This way we avoid the use of corosive chemicals, generate almost no liquid waste and making the whole process more eco-friendly and energy economical. An additional advantage to our type of separation is the potential for direct fucntionalization of the metal from the from oxide. We have specifically looked at the separation of zinc, nickel, and copper. We are currently applying our methods towards more efficient lanthanide separations.
Pharmaceuticals and Medicinal Mechanochemistry
Our research interest surrounds the synthesis of
biologically active and pharmaceutically relevant organic
compounds via the use of mechanochemistry and sonochemistry, as
an alternative route that is more environmentally benign when
compared to traditional methodologies.
We have recently developed a greener and more highly efficient protocol for the direct synthesis of unsymmetrical thioureas and sulfonyl-(thio)urea compounds through ball milling mechanochemistry via a click mechanochemical coupling of the respective amines, sulfonamides and (thio)isocyanates without the use of bulk organic solvents. While inherently poor nucleophilicity of the sulfonamide nitrogen atom reduces its reactivity in addition reactions, we reported the use of potassium carbonate as a mild, environmentally benign base for the deprotonation of the sulphonamide group as well as a catalytic coupling between the sulphonamide and (thio)isocyanate via the use of substoichiometric amounts of CuCl. Furthermore, a second generation anti-diabetic sulfonyl-urea drug, Glibenclamide, has also been successfully synthesized by combining the amide bond formation with base-assisted and CuCl-catalyzed sulfonamide addition to cyclohexylisocyanate in a two-step mechanochemical fashion. We are currently investigating the mechanism for the Cu-catalyzed sulfonamide coupling and expanding this methodology to other synthetic reactions.
One of our main goals includes the development of mechanochemistry for organometallic synthesis, in particular to conduct oxidative addition, one of the fundamental reaction types of organometallic chemistry. Mechanochemical reactions have recently demonstrated impressive potential for improving the speed, energy- and materials-efficiency of chemical reactions, and especially so in organic chemistry, metal-organic synthesis and syntheses of molecular solids. However, the potential of mechanochemistry in organometallic synthesis has remained almost completely unexplored. In addition to the rhenium complexes below we are investigating both ruthenium based olefin metathesis.
Recently we describe the first application of mechanochemistry to conduct a fundamental transformation of organometallic chemistry: oxidative addition.1 By using simple organometallic rhenium(I) precursors as model compounds, we have demonstrated for the direct oxidative addition of halogens (Cl, Br and I) onto a metal centre via a mechanochemical procedure that, unlike all relevant solution procedures reported in almost 50 years, does not require solvent, elementary halogens, or photochemical and high-pressure treatment. Instead, the mechanochemical procedure utilises a conventional oxidation agent in combination with readily available metal halides.
Our lab has pioneered the development of mechanochemical olefin metathesis reactions using commercially available ruthenium complexes. This rapid, room-temperature approach enables us to minimize the amount of solvents needed in these high-yielding reactions.
Our group is strongly committted to improving the quality of chemistry education at the undergraduate level by designing new experiments for our teaching labs. Currently we are focused on generating modern experiments involving mechanochemistry for introductory undergraduate courses. We are developing new green chemistry experiments that enable students to evaluate the cost and sustainability of various synthetic methods. In addition, we are focusing efforts on generating new conceptual frameworks for designing upper year teaching labs in order to better integrate important concepts in chemistry into experiments that highlight current challenges in research and teach fundamental lab techniques.
Nanoparticles with Moores Group
In collaboration with the Moores Group we have recently investigated the syntheses of ultra-small nanoparticles using our ball milling technique. We report gram scale syntheses of gold nanoparticles with diameters between 1-4nm, and bismuth sulfide nanoparticles with diamaters around 2nm. The significance of this work is that we manage to avoid the use of external reducing agents or bulk solvents which are typically required for nanoparticle synthesis. We believe that this presents a new scalable, cost effective, and environmentally benign synthesis of nanoparticles
Redox Driven Self-Assembly with the Lumb Group
Our collaboration with the Lumb Group is focused on combining solid state oxidations and coordination driven self-assembly to achieve the nearly waste-free synthesis of novel metal organic materials with magnetic properties. Additionally, such protocols can be used to create germanium based advanced materials and synthetic precursors, without the need for chlorine.
Azobenzenes with Barrett Group
In a collaboration with the Barrett group, perhalogenated cis-azobenzenes have shown the first photomechanical isomerization which permanently modifies crystal shape. This thermally irreversible change involves a large change in crystal shape, and importantly is controlable. It is the first time an irreversible photomechanical change in crystal shape has been reported in azobenzenes.
Fluorescence with Cosa Group
Working with members of the Cosa group who specialize in fluorescence, we have use solid state fluorescence to monitor and characterize polymorphs, solvates, and cocrystals of pharmaceutical molecules. This provides our group with the important ability to quantify the amounts of amorphous and crystalline phases as well as monitor kinetics of interconversion. We hope to expand this technique to other types of solid material as well as mechanochemical processes.