Dimeric phenalenyl-based neutral radical molecular conductors
by Chi, X.; Itkis, M. E.; Kirschbaum, K.; Pinkerton, A. A.; Oakley, R. T.; Cordes, A. W.; Haddon, R. C.
We report the preparation, crystallization, and solid-state characterization of ethyl (3)- and butyl (4)-substituted spiro-biphenalenyl radicals. Both of these compounds are found to be conducting face-to-face pi -dimers in the solid state but with different room-temperature magnetic ground states. At room temperature, 4 exists as a diamagnetic is-dimer (interplanar separation of similar to3.1 Angstrom), whereas 3 is a paramagnetic pi -dimer (interplanar separation of .similar to3.3 Angstrom), and both compounds show phase transitions between the paramagnetic and diamagnetic forms. Electrical resistivity measurements of single crystals of 3 and 4 show that the transition from the high-temperature paramagnetic pi -dimer form to the low-temperature diamagnetic pi -dimer structure is accompanied by an increase in conductivity by about 2 orders of magnitude. This behavior is unprecedented and is very difficult to reconcile with the usual understanding of a Peierls dimerization, which inevitably leads to an insulating ground state. We tentatively assign the enhancement in the conductivity to a decrease in the on-site Coulombic correlation energy (U), as the dimers form a super-molecule with twice the amount of conjugation.
- Journal
- Journal of the American Chemical Society
- Volume
- 123
- Issue
- 17
- Year
- 2001
- Start Page
- 4041-4048
- URL
- https://dx.doi.org/10.1021/ja0039785
- ISBN/ISSN
- 1520-5126; 0002-7863
- DOI
- 10.1021/ja0039785