Conducting Charge-Transfer Salts Based on Neutral Pi-Radicals

by Bryan, Clinton Dave; Cordes, A. Wallace; Fleming, R. M.; George, Noel A.; Glarum, Sivert H.; Haddon, Robert C.; Oakley, Richard T.; Palstra, Thomas T. M.; Perel, A. S.; Schneemeyer, Lynn F.; Waszczak, Joseph V.

MOST molecular conductors rely on charge transfer to create carriers. For example, the ET salts1 are hole-doped whereas the C60 salts2 are electron-doped. Neutral radical species in which bands are formed by pi-orbital overlap would be expected to have half-filled bands and thus to be conducting3, but no such metals have yet been reported. Here we report the synthesis and characterization of a molecular conductor which combines both of these approaches: energy bands are formed from one-dimensional stacks of neutral pi-radicals, and the material is rendered conducting by electron transfer from the conduction band following doping with an acceptor. The radical species is the 1,4-phenylene-bis(dithiadiazolyl) diradical 1,4-[(S2N2C)C6H4(CN2S2)] (2 in Fig. 1), reaction of which with iodine vapour leads to crystals of [2][I]. At low temperatures this compound is essentially a diamagnetic insulator, but above 200 K the conductivity and magnetic susceptibility increase markedly, and at room temperature the conductivity reaches 100 S cm-1, which is comparable to that shown by conventional molecular charge-transfer salts.

Journal
Nature
Volume
365
Issue
6449
Year
1993
Start Page
821
ISBN/ISSN
1476-4687; 0028-0836
DOI
10.1038/365821a0