TY - JOUR
T1 - Crystallographic and molecular mechanics investigation of an order-disorder transition and dimorphism in 5H,10H-dithiolo[2,3-b]-2,5-benzodithiocine-2-thione
AU - Chohan, Z H
AU - Harrison, W T A
AU - Howie, R A
AU - Milne, B F
AU - Wardell, J L
PY - 2000
Y1 - 2000
N2 - Single-crystal X-ray structures are presented for three forms of 5H,10H-dithiolo[2,3-b]-2,5-benzodithiocine-2-thione. The alpha (at 150 K) and alpha' (at ambient) forms are very similar and differ only in the presence of crystallographic m symmetry in the molecules of alpha', which is absent in the case of alpha. This pair is related by an order-disorder transition. The beta phase (also determined at 150 K) has a different structure in terms of the molecular packing from either of the other two and therefore constitutes a true polymorph. Molecular mechanics calculations indicated that the most stable CHCl3-solvated conformations for the title compound were a pair of twisted U-shaped enantiomers, U-R and U-L, i.e. similar to the arrangements found in the alpha and beta phases, with the low-lying saddle point between them corresponding to the situation in the alpha' phase. These calculations also indicated that the most stable CHCl3-solvated conformation for the related dibromo-5H,10H-dithiolo[2,3-b]-2,5-benzodithiocine-2-thione was Z-shaped, in agreement with the crystal structure determined earlier for its DMSO solvate [Wang et al. (1998). Synthesis, pp. 1615-1618].
AB - Single-crystal X-ray structures are presented for three forms of 5H,10H-dithiolo[2,3-b]-2,5-benzodithiocine-2-thione. The alpha (at 150 K) and alpha' (at ambient) forms are very similar and differ only in the presence of crystallographic m symmetry in the molecules of alpha', which is absent in the case of alpha. This pair is related by an order-disorder transition. The beta phase (also determined at 150 K) has a different structure in terms of the molecular packing from either of the other two and therefore constitutes a true polymorph. Molecular mechanics calculations indicated that the most stable CHCl3-solvated conformations for the title compound were a pair of twisted U-shaped enantiomers, U-R and U-L, i.e. similar to the arrangements found in the alpha and beta phases, with the low-lying saddle point between them corresponding to the situation in the alpha' phase. These calculations also indicated that the most stable CHCl3-solvated conformation for the related dibromo-5H,10H-dithiolo[2,3-b]-2,5-benzodithiocine-2-thione was Z-shaped, in agreement with the crystal structure determined earlier for its DMSO solvate [Wang et al. (1998). Synthesis, pp. 1615-1618].
M3 - Article
VL - 56
SP - 1011
EP - 1017
JO - Acta Crystallographica Section B, Structural Science
JF - Acta Crystallographica Section B, Structural Science
SN - 0108-7681
ER -