 The most common rhenium chlorides are <unk> , <unk> , <unk> , and <unk> . The structures of these compounds often feature extensive Re @-@ Re bonding , which is characteristic of this metal in oxidation states lower than VII . Salts of [ <unk> ] 2 − feature a quadruple metal @-@ metal bond . Although the highest rhenium chloride features Re ( VI ) , fluorine gives the <unk> Re ( VII ) derivative rhenium heptafluoride . <unk> and iodides of rhenium are also well known . 
