Preparation and characterization of a neutral pi-radical molecular conductor

Citation
Tm. Barclay et al., Preparation and characterization of a neutral pi-radical molecular conductor, J AM CHEM S, 121(5), 1999, pp. 969-976
Citations number
54
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry & Analysis",Chemistry
Journal title
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
ISSN journal
0002-7863 → ACNP
Volume
121
Issue
5
Year of publication
1999
Pages
969 - 976
Database
ISI
SICI code
0002-7863(19990210)121:5<969:PACOAN>2.0.ZU;2-W
Abstract
The synthesis and solid-state characterization of the heterocyclic pi-radic al 1,2,5-thiadiazolo[3,4-b]-1,2,3-dithiazolo[3,4-b]pyrazin-2-yl, 1,2,3-TDTA , is described. The ESR spectrum of 1,2,3-TDTA (in CH2Cl2, 293 K, g = 2.009 ) confirms a highly delocalized spin distribution, with observable hyperfin e coupling to all five nitrogen atoms of the tricyclic molecule (a(N) = 0.5 14, 0.343, 0.109, 0.051, and 0.035 mT). While chemical and electrochemical oxidation (E-1/2(ox) = 1.14 V vs SCE) of 1,2,3-TDTA requires relatively har sh conditions, reduction is extremely facile (E-1/2(red) = 0.15 V vs SCE). More importantly both the observed cell potential E-cell and computed (MNDO ) gas-phase enthalpy Delta H-disp for the disproportionation of this and ot her 1,2,3-dithiazolyls are significantly lower than those observed for thei r 1,3,2-isomers. Crystals of 1,2,3-TDTA are monoclinic P2(1)/n, with a = 6. 6749(16) Angstrom, b = 11.7178(14) Angstrom, c = 8.6148(14) Angstrom, beta = 103.297(16)degrees, and Z = 4. The crystal structure consists of slipped stacks of head-to-tail (centrosymmetric) pi-dimers. The closest intradimer S- - -S contact (S2- - -S3) is 3.2331(15) Angstrom. Variable-temperature ma gnetic susceptibility measurements establish that 1,2,3-TDTA is essentially diamagnetic at room temperature. The magnetic data, along with the results of variable-temperature single-crystal conductivity measurements (1,2,3-TD TA exhibits a room-temperature conductivity sigma = 1 x 10(-4) S cm(-1)), a re interpreted in terms of one-dimensional hopping mechanism for charge tra nsport.