STRUCTURES AT 293-K AND 100-K OF TA-TETRAKIS[BIS(ETHYLENEDITHIO)TETRATHIAFULVALENE] TETRACYANONICKELATE(II) - BETA-[BEDT-TTF]4[NI(CN)4]

[C10H8S8]4[Ni(CN)4], M(r) = 1701.53, F(000) = 864, lambda(Mo Kalpha) = 0.71073 angstrom. At 293 K: triclinic, P1BAR, a = 9.677 (7), b = 10.9 60 (6), c = 16.392 (8) angstrom, alpha = 95.95 (5), beta = 97.85 (5), gamma = 115.13 (5)degrees, V = 1533 (4) angstrom3, Z = 1, D(x) = 1.842 g cm-3, mu = 14.06 cm-1, R = 0.031 based on 3565 observed reflections with I greater-than-or-equal-to 6sigma(I). At 100 K: triclinic, P1BAR , a = 9.721 (4), b = 10.761 (4), c = 16.431 (5) angstrom, alpha = 95.8 7 (3), beta = 98.17 (4), lambda = 115.71 (3)degrees, V = 1507 (2) angs trom3, Z = 1, D(x) = 1.875 g cm-3, mu = 14.31 cm-1, R = 0.082 based on 3865 observed reflections with I greater-than-or-equal-to 6sigma(I). The C atoms of the terminal ethylenic groups of each independent BEDT- TTF molecule are statistically distributed on both sides of the molecu lar mean plane at room temperature. This phenomenon disappears at 100 K where the BEDT-TTF molecules adopt different conformations. The orga nic molecules develop tetramerized stacks along the [210] direction. T he structure belongs to the beta type of the BEDT-TTF series.