Chemical structure of Mn12(acetate)16.
A University of Nottingham team of physicists and chemists have demonstrated for the first time the way in which an irregularly shaped molecule is adsorbed on a surface. It gives important information to scientists on how these molecules could be arranged to form structures, potentially to build tiny new data storage devices which are many times smaller than their existing silicon-based counterparts. Many of the more irregularly-shaped molecules have extremely useful properties — if we can store information on a single molecule which is normally around one nanometre, as opposed to the silicon-based equivalent of 40 to 50 nanometres, we could potentially build devices which are much smaller in size but have a much denser storage capacity.
The work has involved computer modelling a manganese-based molecule — shaped like a concave ‘jam doughnut’ — and predicting how it would be adsorbed on a gold surface before observing its actual behaviour in the lab. Due to the fragile nature of the molecules, the team had to use a novel electrospray deposition technique to get the molecules onto the surface without destroying their functionality.
Calculated configuration of Mn12(acetate)16 on Au(111).
The spontaneous ordering of molecules into two-dimensional self-assembled arrays is commonly stabilized by directional intermolecular interactions that may be promoted by the addition of specific chemical side groups to a molecule. In this paper, we show that self-assembly may also be driven by anisotropic interactions that arise from the three-dimensional shape of a complex molecule. We study the molecule Mn12O12(O2CCH3)16(H2O)4 (Mn12(acetate)16), which is transferred from solution onto a Au(111) substrate held in ultrahigh vacuum using electrospray deposition (UHV-ESD). The deposited Mn12(acetate)16 molecules form filamentary aggregates because of the anisotropic nature of the molecule–molecule and molecule–substrate interactions, as confirmed by molecular dynamics calculations. The fragile Mn12O12 core of the Mn12(acetate)16 molecule is compatible with the UHV-ESD process, which we demonstrate using near-edge X-ray adsorption fine-structure spectroscopy. UHV-ESD of Mn12(acetate)16 onto a surface that has been prepatterned with a hydrogen-bonded supramolecular network provides additional control of lateral organization.
Mn12(acetate)16 adsorbed on a supramolecular network.