Trithioarsenite

Trithioarsenite, also called sulfarsenite, is the trianion AsS3(3−). It is a pyramidal anion, as is typical of other As^{III}X3 compounds. It is generated by treatment of As2S3 with a sulfide:
 * As2S3 + 3 S(2−) → 2 AsS3(3−)

A fundamental synthetic trithioarsenite is Na3As3, which features the pyramidal AsS3(3−).

Thioarsenites are components of many sulfosalt minerals. An example is relatively common mineral proustite, Ag3AsS3,  which is silver(I) trithioarsenite.