CONFORMATIONAL STUDIES ON [16]ANES4 - STRUCTURES OF ALPHA-[16]ANES4 AND BETA-[16]ANES4 ([16]ANES4=1,5,9,13-TETRATHIACYCLOHEXADECANE)

Three morphologies - acicular (alpha), lamellar (beta) and columnar (g amma) are observed for crystals of [16]aneS4 (1,5,9,13-tetrathiacycloh exadecane). The absolute structures of the alpha and beta forms have b een determined: the molecular structures are essentially the same but the two forms differ in their crystal packing. Alpha-[16]aneS, crystal lizes in the orthorhombic space group Pbc2(1) while beta-[16]aneS4 cry stallizes in the monoclinic space group P2(1). The conformation of the molecules is unusual: whereas the other tetrathia macrocycles [12]ane S4 and [14]aneS4 have exclusively exo S atoms, in [16]aneS4 only two l ie in exo positions and this structural feature is related to the chem ical properties of the macrocycle. Molecular mechanics calculations ha ve been carried out on selected conformers of [16]aneS4 and the result s compared with the observed crystal structures and with the hydrocarb on analogue, C16H32. Gamma-[16]aneS4 appears to crystallize in the ort horhombic space group Fdd2 but it suffers from twinning and no structu ral information could be obtained.