A NEW POLYMORPHIC MODIFICATION OF TETRATHIAFULVALENE - CRYSTAL-STRUCTURE, LATTICE ENERGY AND INTERMOLECULAR INTERACTIONS

The molecular and crystal structure of the previously unknown modification of 2,2'-bi-1,3-dithiole (tetrathiafulvalene or TTF) has been determined by X-ray diffraction. The crystal is triclinic, at 298 K, a = 8.379(2), b = 12.906(3), c = 8.145(2) angstrom, alpha = 98.91(3), beta = 96.62(3), gamma = 100.44(3)-degrees, V = 846.4(4), Z = 4, space group P1BAR. The molecular geometrical parameters of this modification (TTF2) do not differ from those found for the known modification (TTF1). However, the crystal structures are rather different. Only infinite chains formed by intermolecular interactions between S atoms of the closest molecules have been found in TTF2, in contrast to TTF1 monoclinic modification (space group P2(1)/c), in which all molecules of the cell are stacked along the short b axis. The two structures have been used as the basis for a reexamination of the idea of a van der Waals radius for sulfur and the comparison and evaluation of various atom...atom potential energy forms and parameters which include interactions involving sulfur atoms.