Professor Malcolm Halcrow

Profile

I gained my Ph.D. in 1992 from the University of Edinburgh, then undertook post-doctoral work in the Laboratoire de Chimie de Coordination du CNRS in Toulouse, France and at Indiana University in the USA. After four years as a Royal Society Research Fellow at the University of Cambridge, I moved to the University of Leeds in 1998, where I'm currently Professor of Inorganic Chemistry. I've held visiting appointments in Japan at Nagoya University (2009) and Osaka University (2017 and 2019), and at Xiamen University in China (2015).

Responsibilities

• Director of Postgraduate Studies

Research interests

My group's interests include the synthesis and structural characterisation of spin-crossover complexes and other switchable coordination compounds, metal/organic supramolecular chemistry and crystal engineering. As such, our research involves both organic and inorganic synthesis, together with extensive use of crystallography, NMR, magnetic measurements, DFT calculations and other analytical techniques. Some of the more specialist measurements are carried out with collaborators in the UK, France, Russia, India and the US.

Spin-Crossover materials
Spin-crossover iron(II) complexes can switch reversibly between a pale-coloured, paramagnetic high-spin state to a dark-coloured, diamagnetic low-spin state. This transition can be induced by changing temperature, by laser irradiation or by some other physical stimulus. While the phenomenon has been known for eighty years, there is still intense worldwide interest in these thermochromic and photochromic switches, which have been used in display and memory devices. We are pursuing new spin-crossover materials with technologically favourable properties, and which is a problem of crystal engineering as well as of ligand design. We are also involved in interdisciplinary projects to incorporate spin-crossover centres into nanostructures and other types of functional material; and, to apply our expertise to other areas where metal ion spin states are relevant, such as synthetic and biological catalysis by base metals.

Mixed-Valent Radical Complexes
We are investigating metal complexes containing multiple redox-active organic ligand centres, with a view to obtaining 'mixed-valent' products containing both oxidised and unoxidised ligand redox sites. Such compounds are intensely coloured with strong visible and NIR absorptions, which reflect unpaired-electron delocalisation around the ligand mixed-valent ligand. Understanding the mechanism of this unusual delocalisation requires in-depth electrochemistry, EPR and UV/vis/NIR spectrocopies, and DFT calculations. Near-IR absorbers like these, whose absorptions can be switched on and off electronically, can be very useful in fibre-optic communications devices.

Manipulating Jahn-Teller Phenomena in Copper Chemistry
Several years ago, we discovered that the electronic structures of certain six-coordinate copper(II) complexes can be changed using sterically or conformationally restricted ligands. In this way, we produced the first true examples of molecular six-coordinate copper(II) compounds with axially compressed, rather than elongated, structures. Although other such compounds had been claimed previously, most of these were subsequently found to be crystallographic or spectroscopic artifacts. We have recently returned to this chemistry, to try and induce similar effects using more subtle physical triggers. We are aiming to produce an EPR-based sensor, where the Jahn-Teller structure of a copper reporter group is changed by a guest binding event.

Inorganic Supramolecular Chemistry
Pyrazole rings contain both Lewis basic (N: donor) and Lewis acidic (N-H donor) groups in close proximity to each other. We are interested in using pyrazole derivatives as ligands that coordinate to cations and anions at the same time; that is, as ligands for metal salts. On one hand, we can use hydrogen-bonding interactions between metal centres and anion guests to template unusual metal-organic network structures or cluster compounds. Alternatively, we can use pre-formed metal centres containing this type of functionality as supramolecular hosts for anions. Both aspects of this chemistry are being pursued.

Qualifications

• PhD, University of Edinburgh, 1992
• BA(Hons), University of Cambridge, 1988

Professional memberships

• Fellow of the Royal Society of Chemistry (FRSC)
• Chartered Chemist (CChem)

Student education

I teach various aspects of the inorganic chemistry part of the Chemistry programme. This includes lectures on the structures and reactions of transition metal compounds; organometallic chemistry; and on the electronic and magnetic properties of inorganic materials. I also hold weekly tutorials on these modules, and on other aspects of the inorganic chemistry curriculum. I demonstrate part of the practical course in the Priestley undergraduate lab, and supervise BSc and MChem research projects.
In addition to the above, I give lectures on chemical bonding to students at the Southwest Jiaotong University/Leeds University Joint School in Chengdu, China.

Research groups and institutes

• Crystallisation and Directed Assembly

Current postgraduate researchers

• Gavyn Chesher

Projects

<li><a href="//phd.leeds.ac.uk/project/128-metal-complexes-of-radical-ligands-–-electron-hopping-leading-to-novel-optical-properties">Metal Complexes of Radical Ligands – Electron Hopping Leading to Novel Optical Properties</a></li>