1,4,7-Trithiacyclononane, also called 9-ane-S3, is the heterocyclic compound with the formula (CH2CH2S)3. This cyclic thioether is most often encountered as a tridentate ligand in coordination chemistry. 9-ane-S3 forms complexes with many metal ions, including those considered hard, such as copper(II) and iron(II). Most of its complexes have the formula [M(9-ane-S3)2]2+ and are octahedral. The point group of [M(9-ane-S3)2]2+ is S6.