The　electronic　and　structural　properties　of　ReO5-　and　ReO5　clusters　are　investigated　using　density　functional　theory　(DFT)　calculations.　The　lowest　energy　structures　for　both　the　anionic　and　neutral　clusters　are　determined,　and　the　corresponding　photoelectron　spectrum　is　simulated.　Our　results　show　that　ReO5-　can　be　described　as　an　unusual　peroxo　molecule,　Re(O)(3)(eta(2)-O-2)(-),　while　ReO5　is　found　to　be　exhibiting　the　O-2(-center　dot)　radical　character.　Molecular　orbital　analyses　and　spin　density　analyses　are　performed　to　elucidate　the　chemical　bonding　and　the　electronic　and　structural　properties　in　these　two　rhenium　oxide　clusters.