A sulfonium ion is a positively charged ion featuring three organic substituents attached to sulfur, with the formula [RS]. Together with their negatively charged counterpart, the anion, the compounds are called sulfonium salts. An oxosulfonium ion is a positively charged ion featuring three organic substituents and an oxygen attached to sulfur, with the formula [RS=O]. Together with their negatively charged counterpart, the anion, the compounds are called oxosulfonium salts. Related species include alkoxysulfonium and chlorosulfonium ions, [RSOR] and [RSCl], respectively.