S. Larsen, T. Thorsteinsson, S. Bøwadt, T. K. Hansen, K. S. Varma, J. Becher and A. E. Underhill.
Acta Chem. Scand. 45, 709-715 (1991).

Abstract
Three precursors to organic donors based on BEDT-TTF have been prepared. 2,3-dihydro-1,3-dithiolo[4,5-e][1,4]dithiin-6-thione (1), 2,3-dihydro-2-phenyl-2-oxo-3-phenyl-1,3-dithiolo[4,5][1,4]dithiin-6-thione (2) and 2,3-dihydro-2-phenyl-1,3-dithiolo[4,5-e][1,4]dithiin-6-thione (3). The crystal structures have been determined from low-temperature X-ray diffraction data. They crystallize in monoclinic space groups as follows. Compound 1 in P21/n with a=10.600(2), b=5.7887(8), c=13.436(3) Å beta=93.03(2)°, Z=4; 2801 reflections gave R=0.030. Compound 2 in P21/c with a=10.0792(13), b=6.059(2), c=20.578(5) Å, beta=105.87°, Z=4; 2490 reflections gave R=0.031. Compound 3 in C2/c with a=15.735(13), b=9.1996(9), c=16.478(14) Å, beta=96.85(3)°, Z=8; 3510 reflections gave R=0.044. Compound 3 displays disorder of the ethylene group. The molecular geometries of these compounds are similar to those found in the salts of the related dimers BEDT-TTF. Short S-S intermolecular interactions influence the packing in 1-3. These interactions are comparable to and even shorter than those found in BEDT-TTF salts.