Research

The Pike group is part of the Synthesis and Catalysis and Energy Materials Research Groupings in the Department of Chemistry at the University of Warwick and engage closely with the Solid State Chemistry Group (with Walton, Senn, Hope, Karasulu groups).

Pike group research interests lie at the interface between molecules and materials. In particular, we are designing new metal-oxo cluster molecules. These molecules can be considered tiny versions of well-known semiconducting materials e.g. ZnO or TiO₂, however at such small sizes the structures are well defined and we can probe reactivity and mechansism using molecular characterisation techniques (e.g. NMR spectroscopy, singe crystal X-ray crystallography). These cluster species have potential uses in (photo)catalysis and as building blocks or precursors to functional materials.

We are particularly interested in understanding the atomic structure of these molecules (by techniques such as X-ray crystallography), and locating potential active sites for well-defined catalytic processes. We study light-induced single-crystal to single-crystal transformations to understand photoreactivity and mechanism in precise cluster molecules.

Highlighted Publications:Photoinitiated Single-Crystal to Single-Crystal Redox Transformations of Titanium-Oxo Clusters.

In partnership with collaborators, we study the electronic structure of these systems. The combination of metal and oxygen orbitals begins to form ‘bands’ of molecular orbitals as the clusters become larger in size and act less like molecules and more like materials. Quantum size effects can alter the energies of frontier orbitals in oxide materials, but this is dependent on the specific system e.g. size effects are observed in TiO₂ but not in CeO₂.

Highlighted Publications: Size-dependent electronic structure of titanium-oxo-alkoxides: exploring quantum confinement at the smallest sizes

Photoabsorption of 1-2 nm Molecular Ce-oxo Nanoclusters Versus Ceria: Intervalence Charge Transfer but No Size Effects

Synthesis of a nanoscale Cu(II)31-oxo-carboxylate cluster, and effect of Cu-oxo cluster size on visible-light absorption

By utilising a range of spectroscopic techniques we can understand photoredox reactivity that occurs when we irradiate a cluster with light. This can give insight into processes that can occur at semiconductor surfaces and will lead to new photocatalysts. We have a particular interest in Ti-oxo-alkoxide clusters, which provide opportunity to study photoreaction mechanism in detail.

Highlighted publications: Switching on photoreactivity in Ti₄-oxo clusters by increasing the size of 1,n-alkane diolate bridging ligands

Photoactivation of titanium-oxo cluster [Ti₆O₆(OⁱPr)₆(O₂C^tBu)₆]: mechanism, photoactivated structures, and onward reactivity with O2 to a peroxide complex

Photo-redox reactivity of titanium-oxo clusters: mechanistic insight into a two-electron intramolecular process, and structural characterisation of mixed-valent Ti(III)/Ti(IV) products

Well-defined multi-metallic clusters can also act as ideal single-source precursors for functional materials, for example, cluster molecules containing Bi and V can be heated to prepare BiVO₄ thin films useful as photoanodes for photoelectrochemical water splitting. We are fascinated by what happens along the pathway of a molecule to material transformation, our recent studies demonstrate that there is a lot to discover in this chemical space!

Highlighted publications: Amorphous intermediates and discovery of a kinetic polymorph of BiVO4 from heating V+Bi+Zn single-source precursors

Single‐Source Bismuth (Transition Metal) Polyoxovanadate Precursors for the Scalable Synthesis of Doped BiVO₄ Photoanodes

The use of mixed-metal single source precursors for the synthesis of complex metal oxides

We specialise in utilising reactive organometallic, metal amide and metal alkoxide reagents to build our clusters. The group use our own glovebox and Schlenk lines in the lab to ensure air free conditions for these reactions.

Highlighted publications: Hydrolysis of organometallic and metal–amide precursors: synthesis routes to oxo-bridged heterometallic complexes, metal-oxo clusters and metal oxide nanoparticles

Seb's previous research projects include:

• Understanding the synthesis, redox reactivity and catalytic potential of nanoparticles

Highlighted publications: Simple Phosphinate Ligands Access Zinc Clusters Identified in the Synthesis of Zinc Oxide Nanoparticles.

Colloidal Cu/ZnO Catalysts for the Hydrogenation of Carbon Dioxide to Methanol: Investigating Catalyst Preparation and Ligand Effects

Reversible Redox Cycling of Well-Defined, Ultrasmall Cu/Cu₂O Nanoparticles.

• Organometallic chemistry within the solid state

Highlighted publications: Stoichiometric and Catalytic Solid-Gas Reactivity of Rhodium Bis-Phosphine Complexes.

Solid-State Synthesis and Characterization of σ-Alkane Complexes

Synthesis and Characterization of a Rhodium(I) σ-Alkane Complex in the Solid State.

Tom making copper rainbows in the lab!

Ce-oxo clusters also called 'molecular nanoparticles'

Crystal structure of a complex containing Bi, V and Co metals, useful as a single source precursor to access Co-doped BiVO₄ for photoelectrochemical water oxidation.

Colour change of a titanium-oxo cluster upon exposure to UV light.

1 nm sized Ti-oxo cluster