Vinylogous Tetrathiafulvalene (TTF) π-Electron Donors and Derived Radical Cations: ESR Spectroscopic, Magnetic, and X-ray Structural Studies

The properties of new 2,2‘-ethanediylidene(1,3-dithiole)
derivatives 5, 6, and
8−11 are
reported. Cyclic voltammetric studies establish that they are
efficient donor molecules, with
the extended conjugation resulting in stabilization of dications,
relative to tetrathiafulvalene
TTF (1). Radical cations are generated by oxidation of
the neutral compounds with
trifluoroacetic acid or anhydrous silver perchlorate in
dichloromethane, and their ESR and
proton ENDOR spectra are reported. The bulk of the spin population
resides in the central
S2CCCCS2 part of the π-system.
The X-ray crystal structure of donor 6 reveals
that
the 2,2‘-ethanediylidene(1,3-dithiole) framework is planar.
Donor 6 forms a crystalline 1:1
charge-transfer complex with TCNQ, the X-ray crystal structure of which
shows a mixed
stack structure. A solution of this complex in acetonitrile
exhibits ESR spectra of both radical
ions, 6·+ and TCNQ·−.
Static susceptibility data are reported for TCNQ complexes of
some
of these donors.