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Our research encompasses the synthesis and application of molecules and materials.

Photocatalysis

Photocatalysts are a class of materials that mediate chemical reactions using photons as a source of energy. There are many potential uses including the degradation of chemicals detrimental to the environment and the conversion of solar into chemical energy. We are interested in the later application, specifically the production of dihydrogen and dioxygen from water that provides the basis for a clean fuel source with zero carbon emissions. Simplistically the concept is shown in figure 1. A photon is absorbed by a semiconductor causing electron excitation from the valence to conduction band. The excited electron can be used for reduction chemistry and the hole for oxidation chemistry. Many materials exhibit exciton (an electron-hole pair) formation that can be used for useful chemical reactions. However, significant challenges remain dependent on the application, including efficiency, photocatalyst stability and the use of visible (low energy) photons present in the solar spectrum. It is therefore necessary to identify and study new photocatalytic materials.

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Fig. 1

We have recently built a testing facility and microwave plasma reactor (figure 2) to discover new materials for photocatalytic applications. The use of microwave-induced plasmas (MIP) builds on some of our earlier work exploring the synthesis of materials using microwave methods.

Microwave heating is a well established technique for solution based synthetic chemistry and most modern molecular laboratories now contain a microwave reactor. Commonly, rapid reaction rates can be achieved because of superheating that is a result of coupling between the solvent (or reactants) and microwave radiation. Similarly in the solid state one of the components of a reaction must couple with the microwaves, generating heat via dielectric or conduction losses to drive a reaction. Solids can heat at enormous rates (100 K/s), however many of interest do not couple with microwaves at room temperature limiting the application of this technique to preparative materials chemistry.

We have designed and constructed a reactor capable of initiating and sustaining microwave-induced plasmas of various gases including Ar, N₂, H₂/N₂, NH₃ and O₂. The plasma can be used as a source of heat to drive bulk solid state reactions and also as a source of reactive species for gas-solid reactions for surface or bulk modification.

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Fig. 2

Molecular Chemistry

N-Heterocyclic Carbenes

Our interest in this class of compound has been to prepare new achiral and chiral compounds and investigate their application as ancillary ligands for metal-mediated catalysis. Examples of crystal structures of some metal complex derivatives are shown below.

In addition to their growing popularity over the last 10 years for catalytic applications NHC are also of interest because of their unusual electronic properties and structure. In common with many other groups we are also interested in preparing complexes that may exhibit new stoichiometric reactions that may have future application to new catalytic processes.

9,9'-spirobifluorene

Mainly an undergraduate project, we have been studying SBF primarily because of its aestetic appeal and its electronic structure. Cocrystals with arenes have been prepared to investigate weak C-H interactions; p-coordination of SBF to obtain metallocene complexes; and a tetraacid derivative has been synthesised and used as a building block for layered coordination polymers. The ultimate aims are to utilise the D2d structure and electronic 'p-s-p' system for optoelectronic and gas sorption applications. A few structures are shown below.

SBF and biphenyl 1:1 cocrystal exhibiting C-H...p-arene interactions

[(CpFe)2(h6, h6- SBF)][PF6]2

9, 9'-spirobiflourene-2, 2', 7, 7'-tetracarboxylic acid (SBFTA)

Coordination polymer of SBFTA;Co(II);methylimidazole

Equipment

The department has modern analytical facilities including NMR spectrometers (700, 600, 500, 300, 270 MHz), IR, UV and ESR spectrometers; a CCD diffractometer and mass (ESI, FAB) spectrometers; powder diffraction, TGA, DSC, and BET surface area measurements. Since the foundation of the York Jeol Nanocentre the group has access to an array of electron microscopy facilities including SEM and TEM.

In addition to standard laboratory equipment the group also has its own semi-prep HPLC, GC-MS, autoclaves, carousel reactors and drybox.