Inorganic Chemistry
Electrons provide the bonding between the atoms in any
material, so it is not surprising that electrolysis can bring about
dramatic and precise chemical changes. We have developed a conceptual
approach to exploring molecular electronic structure that combines
electrochemical and spectroscopic methods as explained below.
Computational simulation of electrode response is also a vital aspect
of validating the interpretation of redox behaviour. Redox processes
in simple coordination complexes may turn out to be mainly
metal-centred, truly delocalised or mainly ligand-centred, as with
bipyridyls. In bimetallic clusters, intensely coloured
mixed-valencestates can arise. In all these examples,
electrosynthesis offers a logical route to the unusual oxidation
states, once these have been identified by voltammetry. In particular,
in situ optical spectro-electrochemistry enables quite elusive
species to be studied in depth without isolation.
Dr Heath made two research visits to the Photon Factory synchrotron in Tsukuba, Japan, accompanied the second time by Dr Mahon. Dr Mahon has taken up operation of the UC Raman Microscope Facility, and remains a consultant with cap-XX Pty Ltd. Maria Kubik has joined the group to pursue her doctoral studies on artists' materials. Professor Creagh (U. Canberra) and Dr Otieno-Alego (AFP Forensic Criminalistics) were awarded RSC Visiting Fellowships, attached to the group. Dr Webster (QEII Fellow, 2001–) also retains his association with the group. Jennifer Zampese (U. Canterbury) was our summer scholar for 2002/03, closely assisted by Stephen Lee. Ms Sushilla Knottenbelt and Dr John McGrady (U. York, UK) visited our laboratory between January and March to continue collaboration on redox-active clusters.
For popular electro-analytical electrodes with disk geometry, the discontinuity at the perimeter between the active conducting surface and insulating annulus is a great obstacle to solving the complex differential equations. Previous treatments relied on alternative simplifications appropriate to only the short or long time limits. A hybrid analytical-numerical procedure known as the Integral Equation Method has been used to sufficiently extend the short-time expression. Convolutive Modelling is then applied to predict the response of the disk electrode under either current or potential control. (with P.J. Mahon, and D.K. Cope [North Dakota State U. USA], K.B. Oldham [Trent U. Ontario Canada])
A difficulty in testing apparatus for a.c. voltammetry is that the passive components in normal hard-wired dummy cells are linear and so they fail to simulate the real solution-cell electrochemical response to a.c. modulation. However, in a dummy cell with two opposed diodes connected in series, the reverse bias current of one diode or the other is active whatever the sign of the applied voltage. With suitably chosen elements, the response simulates a pseudo wet-cell over a frequency range. This device enables effective and convenient testing of versatile electrochemical instruments with alternating signal detection modes. (with P.J. Mahon)
Metal cluster compounds are of enduring importance in transition metal chemistry. We have a long-standing interest in confacial bimetallic complexes of the form L3M(µ-X)3ML3. Dr Nick Perkins built extended confacial arrays by attaching two RuL3 fragments to an MX6 or M2X9 core. Linear tetrametallics of type [(R3P)3Ru(µ-X)3Os(µ-X)3Os(µ-X)3Ru(PR3)3]+ with a II,III,III,II resting state show two Os-centred reductions and two Ru-centred oxidations. The pattern of metal-metal bonding changes over the five oxidation states, in accord with the spectro-electrochemical data. (with L. Dubicki, A.J. Edwards, S.B. Lee, P.J. Mahon, N.E. Perkins, R.D. Webster, and S.Z. Knottenbelt, J.E. McGrady [U. York, UK])
Marriage of electrolysis with supposedly incompatible NMR spectroscopy had largely eluded chemists until in 2000 we reported a successful electrogenerative cell for practicable in situ NMR detection. This assembly fits in a normal spinning sample tube in a standard multinuclear FT spectrometer. Redevelopment of the Bramley/Prenzler in situ electrochemical NMR cell has been taken up by Dr Richard Webster as part of his QEII Fellowship program (see elsewhere). In a separate development, collaboration with Melbourne colleagues has given us access to an advanced electrolytic flow-cell for redox-modulated EXAFS measurements on our metal clusters at the Australian Beamline Facility in Tsukuba. (with R. Bramley, M.A. Keniry, R.D. Webster, and separately with S.P. Best, M. Bondin, A. Moreno [U. Melbourne])
Parallelling our in-house research in redox-active inorganic complexes and linear metal arrays is a long-standing interaction with Dr Mark Humphrey and his colleagues on the instrumental characterization of the extended library of organometallic compounds developed under his leadership for application as non-linear optical materials. This has led to a practicable electro-generative non-linear-optical cell, and to systematic correlations linking the optical and redox behaviour of these systems with trends in their molecular and electronic structure. (with S.B. Lee, A.Y. Park, and M.P. Cifuentes, M.G. Humphrey, S.K. Hurst, J.P. Morrall, C.E. Powell, M. Samoc, R. Stranger [Chemistry, ANU])
We are concerned with the scientific conservation of historic items and works of art, as well as technological corrosion in equipment and unwelcome inorganic deposits in internal combustion engines. The Merlin engines of Lancaster bomber G-for-George required such scrutiny before the aircraft's recent return to public display. Surfaces and pigments are studied by many methods, including diffuse reflectance, Raman imaging microscopy, X-ray single-crystal and powder diffraction, and impedance spectroscopy. Particular attention is presently being given to paintings from the 'Angry Penguins' group and other significant works, with the collaboration of the National Gallery of Australia. (with A.J. Edwards, M.E. Kubik, S.B. Lee, P.J. Mahon, R.D. Webster, and R. Maxwell [Art History, ANU], M. Sterns, [Chemistry, ANU], G.L. Bailey [Australian War Memorial], D.C. Creagh, V. Otieno-Alego [U. Canberra], D.L. Hallam, R. Tait [National Museum of Australia])