Hyperfine data and g factors are reported for the radical cations of tetrdthiafuivalene (TTF; 1) and of its derivatives 2-13. From the intense satellite spectra of lt-13f not only the coupling constants of the 33S isotopes in the TTF moiety could be determined, but also, in favourable cases, those of the I3C isotopes in the central double bond. The former values range from 0.370 (8 t ) to 0.470 mT (4 t ) and the latter from 0.255 (8 f ) to 0.360 mT (4 t ) in the radical cations of bis(ethy1enedithio)-TTF (8 + ) and tetracyano-TTF (4 + ). The radical cation of l T F (1 t ) exhibits intermediate values, 0.425 for the 33S and 0.285 mT for the I3C isotopes. The spin population in 1 t-13 t resides, to a large extent, in the central S2C = CS2 part of the n-system. It tends to increase (decrease) by substitution with electron-accepting (donating) groups in the 2,3,6,7-positions of TTF.
Introduction. -Since the discovery of high electrical conductivity in the charge transfer complex of 1,4,5,8-tetrahydro-l,4,5,8-tetrathiafulvalene (TTF; 2-( 1,3-dithiol-2ylidene)-1,3-dithiole; 1) and 7,8-tetracyanobenzo-1,4-quinodimethane (TCNQ) [l], a large number of such 'organic metals' have become known [2] [3]. Most of these superconducting materials are complexes or salts of electron donors structurally related to TTF. The spin distribution in the radical cations of the TTF-based donors is, therefore, of interest for understanding the properties of the pertinent 'organic metals'.
Here, we describe the ESR studies on the radical cations of TTF (1) and of the following compounds derived from TTF by substitution or annelation in the 2,3,6,7-positions: tetramethyl-TTF (TM-TTF; 2-(4,5-dimethyl-l,3-dithiol-2-ylidene)-4,5-dimethyl-1,3-dithiole; 2), tetrakis(trifluoromethy1)-TTF (TTFM-TTF; 2-[4,5-bis(trifluoromethyl)-1,3-dithiol-2-ylidene]-4,5-bis(trifluoromethyl)-1,3-dithiole; 3), tetracyano-TTF (TCN-TTF; 2-(4,5-dicyano-l,3-dithiol-2-ylidene)-1,3-dithiole-4,5-dicarbonitrile; 4), a mixture (5) of 2,6-and 2,7-dimethyl-TTF (2,6-and 2,7-DM-TTF; ]-1,3-dithi01-2-ylidene)-4,6-dihydrothieno-[3,4-d]-1,3-dithiole-S,S,5,5-tetraoxide; 7), bis(ethy1enedithio)-TTF (BEDT-TTF; 2-(5,6dihydrel,3dithiolo[4,5-b][ 1,4]dithiin-2-ylidene>5,6dihydre 1,3-dithiol0[4,5-b][ 1,4]dithiin; S), dithiopheno-TTF (2-thieno[3,4-d]-1,3-dithiol-2-ylidenethieno[3,4-d]-1,3-dithiole; 9), bis(dimethy1thiopheno)-TTF (2-(4,6-dimethylthieno[3,4-d]-1,3-dithi01-2-ylidene)-4,6dimethylthieno[3,4-d]-1,3-dithiole; lo), dibenzo-TTF (DB-TTF; 2-( 1,3-benzodithiol-2-y1idene)-1,3-benzodithiole; l l ) , bis(phenanthro-9,lO)-TTF (2-phenanthro[9,10-d]-1,3dithiol-2-ylidenephenanthro[9,10-d]-1,3-dithiole; 12), and bis(acenaphtho-l,2)-TTF (8- acenaphtho[ 1,2-d][ 1,3]dithiol-8-ylideneacenaphtho[ 1,2-d][ 1,3]dithiole; 13).