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 macrocycle, 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. The compound crystallizes in the monoclinic space group C₂/c with the unit cell dimensions: a = 22.481(1) Å, b = 5.433(2) Å, c = 17.9259(9) Å, and = 117.711(4)°. The conformation adopted by this ligand is such that four of the sulfur atoms are exodentate, but two sulfur atoms are syn endodentate, unusual for a macrocycle of this type. All twelve of the C—S—C—C torsional bond angles in 20S6 are gauche as expected, and the ligand conformation may account for the complexation properties observed for this hexathioether macrocycle.