Characterisation of the Metal-Molecule Interface
The metal-molecule interface plays an important role in organometallic synthesis, catalysis, nano-scale assembly and electron transfer phenomena. We aim to characterise the interaction between a metal atom/cluster and atoms/molecules. Structural, electronic, optical and chemical properties of the interface are to be investigated computationally for a variety of model metal-molecule systems. The anticipated outcomes will provide insight into the physical and chemical properties of metal-molecule interfaces that will be crucial to the future development of nanoscale technologies.
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Principal Investigator Gregory MethaChemistry University of Adelaide |
Project f78 |
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Co-Investigators Magdalene AddicoatMark Buntine Vik Dryza Chemistry University of Adelaide |
RFCD Codes 250104, 250105, 250601 |
Significant Achievements, Anticipated Outcomes and Future Work
During 2003, we have computationally explored the interaction of CO with transition metal trimers, M3, across the periodic table. The specific question we sought to answer was whether the adsorption process retains the molecular CO bond or does it dissociate?
The results for the 4d metal trimers show an interesting and clear trend across the periodic table: Nb, Mo, Ru, Rh and Ag. For all clusters, both a physisorbed "molecular" CO species and a chemisorbed "dissociated" CO species were found. For Nb3 and Mo3, the relative energetics of the dissociated structures was found to be lower in energy. The transition state was found to be below the zero energy of isolated M3 + CO. Hence, for these systems, the dissociative process can be thought to be spontaneous. From Ru onwards, the situation is reversed with the physisorbed species being more energetically favourable. Hence, the most stable form of these species retains the molecular CO group.
We have further explored this result by analysing the electron density of each species using Natural Bond (order) Analysis (NBA) and found a direct correlation with the absolute energy of the pi* anti-bonding orbital of CO in the physisorbed structure. This work is currently being written up for publication.
Our next step is to explore the interaction of CO with mixed metal clusters. For example, our calculations show that CO binds dissociatively to Nb3 but associatively to Rh3. What happens if CO reacts with a mixed metal cluster such as Nb2Rh or Rh2Nb? Does the CO bond become progressively weaker as more niobium atoms are included? If so, it may be possible to precisely tune the strength of the metal cluster–CO bond, and the C–O bond, in a controlled manner. If so, there may be great opportunity to utilise this compositional dependence of reactivity to tune the activity of a metal cluster towards CO and other adsorbate molecules. This has obvious implications in heterogeneous catalysis.
Computational Techniques Used
Almost exclusively, we perform molecular geometry optimisations and frequency calculations using the hybrid density functional code in Gaussian 98.
Publications, Awards and External Funding
External Funding and Awards
None.
Publications
None.