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Research Projects II |
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BACKGROUND Currently there is a great deal of interest in the metal-coordination templated construction of 2-D and 3-D architectures. In many cases, the metal centre involved in the self-assembly process is kinetically labile. The advantage of using such moieties is that the self-assembly process is under thermodynamic control. The cost of using such an approach is that the final product is, by definition, an equilibrium product and, as such, is not kinetically robust.
The Thomas group has developed strategies for the construction of kinetically-locked architectures containing d6-metal centres.[1] WHY? In many cases, the construction of molecular devices for nanotechnology, such as switches and sensors, will require kinetically robust architectures.
2a. VALENCE MIXING BOWLS. In one approach, the properties of thiacrown ligands to labilize metal-ligand bonds at high temperatures has been exploited. Using derivatives of the DNA bases and related molecules as bridging ligands, oligonuclear metallomacrocycles that are kinetically inert at room temperature have been synthesised. For example, adenine derivatives yield trinuclear [RuII([9]aneS3)] complexes, which can be reversibly oxidised into two different mixed valence states. Uniquely, while the [RuII2RuIII] state involves localised electrons hopping between the three metal ions, the formally [RuIIRuIII2] is in fact a delocalised system containing three equivalent “RuII(2/3)” metal ions.[2] The Host-Guest Chemistry of these bowls is now being investigated. |
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Research Projects II |
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2b. HETEROMETALLOMACROCYCLES AS LUMINESCENT SENSORS. In another strategy towards the construction of complex host architectures kinetically robust, photophysically and/or electrochemically-active RuII complexes with free coordination sites are synthesised as “building blocks” and then self-assembled into final architectures using another metal template. Using this approach, mixed metal systems such as the [Ru2Re2] complex shown below have been isolated in good yields. |
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X-ray Structure of Ru2Re2 macrocyclic sensor [Data collection and image courtesy of Drs Sarah Heath and Simon Teat [Image of Metallomacrocycle rendered by Dr Mark Winter] ]
In water these macrocycles are hosts for aromatic molecules, while in organic solvents, such as acetonitrile, binding studies reveal they function as luminescent sensors for anions.[3,4]
COLLABORATIONS ON THIS PROJECT: The detailed X-ray studies on this project were carried out by Dr Sarah Heath (University of Manchester) and Dr Simon Teat (Daresbury Laboratory). Computational studies (DFT) are being carried out by Dr Anthony Meijer (University of Sheffield). |
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Structure of a trinuclear bowl Space filling model of the bowl |
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2. Metal-templated self-assembly of kinetically-locked architectures. |
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REFERENCES 1. “Kinetically locked self-assembly,” J. A. Thomas, Chem. Soc. Rev., 2006, 2007, 36, 856-868. 2. “Switchable electron transfer processes in a mixed valence, kinetically locked, trinuclear RuII metallo-macrocycle,” N. Shan, S. Vickers, H. Adams, M. D. Ward., J. A. Thomas, Angew. Chem. Intl. Ed., 2004, 43, 3398-41. 3. “Hetero-metallomacrocyclic hosts that bind molecular guests in water,” P. de Wolf, S. Heath, J. Thomas, Chem. Commun., 2002, 2540-2541. 4. "Self-assembled kinetically locked RuII-based metallomacrocyles: physical, structural, and modeling studies." P. de Wolf, P. Waywell, M. Hanson, S. L Heath, A. J. H. M. Meijer, S. J Teat, J. A. Thomas, Chem. Eur. J., 2006, 12, 2188 - 2195 . |
