Posted on behalf of Josh Campbell, web writer for CrystEngComm
Organic superconductivity has been observed in charge transfer complexes since the 1980s. The organic cation is most commonly a tetrathiafulvalene derivative or a polycyclic aromatic hydrocarbon. Typically the charge is transported through 1D π-stacks, which can be thought of as molecular wires. However interactions between neighbouring wires have a large impact on the properties of the bulk. The preparation of insulated molecular wires can allow for better understanding of the 1D charge transport and better electronic properties. In π-stacked materials bulky counter ions are used to separate the stacks which allows for better solubility and survival of strongly cationic species.
A new paper looks at how TMFB ((trifluoromethyl)phenylborate) counter ions affect the crystalline packing seen across a series of organic donors. Two distinct packing arrangements were seen, with some donors adopting π-stacked chains which were well separated by the counter ion. However others showed an isolated cation radical bonding motif. To investigate this the authors looked at the size of the donors in question and showed that the switch between packing is possibly to do with the product of the width and length of the molecule. The authors also investigated the electronic properties of the stacks, some of which showed excellent electronic properties.
Find out more from the paper:
π-Bonded molecular wires: self-assembly of mixed-valence cation-radical stacks within the nanochannels formed by inert tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anions
Sergiy V. Rosokha, Charlotte L. Stern and Jeremy T. Ritzert
CrystEngComm, 2013, Advance Article
Josh Campbell is a PhD student currently at the University of Southampton studying crystal structure prediction of organic semiconductors. He received his BSc from the University of Bradford.