Academic Staff

Teaching Responsibilities

• CHE2 Inorganic Chemistry
• CHE3 Inorganic Chemistry

Research Expertise

Metal-organic, organometallic and materials chemistry.

Cation - Anion Interactions

Numerous salts are known which contain halogenometallate ions which can be written as [MX_n]^p- and organic-based countercations, e.g. CH₃NH₃⁺ HgCl₃^-. The nature of the metal-containing entity often depends on the counterion and unusual species may result. Thus, the pyridinium salt obtained from Tl(III) chloride in HCl solution contains the bridged dimeric anion [Tl₂Cl₁₀]^4- (Fig. 1), while other salts contain the isolated 5-coordinate [TlCl₅]^2- or chains of TlCl₅]^2- units. From similar Fe(III) systems, we have recently characterized the new [FeCl₅]^2-(Fig. 2), its solvated species and [trans-FeCl₄(H₂O)₂]^- anions.
Thus, in addition to the goal of synthesizing new species with unusual coordination numbers or mixed ligand systems, we aim to come to an understanding of the relationships which govern the nature of these salts in terms of the "secondary" interactions which may be present between the ions. For any given metal system, not only can the size, "shape" and charge of the organic cation can be varied, but also substitutions can be made in aromatic rings, rings may be linked or fused, nitrogen bases can be quaternized or left free to form hydrogen bonds, etc. Such factors can influence the ways in which the metal-containing ions form in their equilibrium systems and the ways in which these anions and their counterions assemble to yield crystalline solids.

Investigation of Materials Properties

This work is carried out in collaboration with Dr. John Liesegang (Department of Physics).
Many compounds of the type listed above have technologically useful properties, e.g. chloroaluminate ionic liquids as ambient temperature reaction media, chloromercurate hydrogen bonded piezoelectrics, or other phase change materials. A major effort is underway to investigate the magnetic properties of the various Fe(III) systems (Mössbauer spectroscopy and magnetic susceptibility measurements) and phase changes are monitored via other physical techniques such as X-ray photoelectron spectroscopy, differential scanning calorimetry and nuclear quadrupole spectroscopy. A major goal is to develop designed (or "rational") syntheses for materials (such that they have specific properties) by starting from known structures and employing computer-based simulations.

Structures of Fungicidal Organotin (IV) Compounds

Recent interest has centered on producing compounds which combine the biocidal R₃Sn entities with anionic groups, X, which themselves are biologically active, so yielding complexes with increased activity and which lead to lower pest resistance. Our activities have concentrated on fungicidal materials for which the maximum effect is obtained when the R group contains around six carbon atoms; hence pure R₃SnX compounds are being synthesized for the series with R = C₆H₆, cyclo-C₆H₁₁ and C₆H₅CH₂ with a range of biologically-active X groups, such as substituted carbamates, carboxylates, thols, amines, etc. Many appropriate anionic groups are potentially chelating, while the relatively large tin radius permits a range of coordination geometries, which are most reliably determined via X-ray crystallography. Recent examples are the compounds with Sn - S bonds (from thiopyridine N-oxide and aminoethanethiol). The fungicidal activities (against a range of test fungi) and spectroscopic parameters of compounds of this type are being correlated with their determined crystal structures.