The crystal structure of the macrocyclic hexathioether 1,4,7,11,14,17-hexathiacycloeicosane: Implications for metal complexation

Several metal complexes of the twenty-membered ring hexathioether macrocycl e, 1,4,7,11,14,17-hexathiacycloeicosane (20S6), have now been prepared and crystallographically characterized. In order to examine structural changes in the ligand which may occur under complexation, we undertook an analysis of the structure of the 20S6 ligand by single crystal X-ray diffraction. Th e compound crystallizes in the monoclinic space group C-2/c with the unit c ell dimensions: a = 22.481(1) Angstrom, b = 5.433(2) Angstrom, c = 17.9259( 9) Angstrom, and beta = 117.711(4)degrees. The conformation adopted by this ligand is such that four of the sulfur atoms are exodentate, but two sulfu r atoms are syn endodentate, unusual for a macrocycle of this type. All twe lve of the C-S-C-C torsional bond angles in 20S6 are gauche as expected, an d the ligand conformation may account for the complexation properties obser ved for this hexathioether macrocycle.