The　structure　and　chemical　bonding　in　the　Re3O3-　cluster　are　investigated　using　photoelectron　spectroscopy　and　density-functional　theory　calculations.　Vibrationally-resolved　photoelectron　spectra　were　obtained,　yielding　an　accurate　electron　affinity　(2.54　±　0.02　eV)　and　a　ground-state　ReO　stretching　frequency　(960　±　30　cm　-1)　for　the　Re3O3　neutral　cluster.　It　is　shown　that　the　Re3O3-　cluster　possesses　a　C　2v　(1A1)　ground-state　structure　consisting　of　a　Re3　triangle　with　one　bridging　and　two　terminal　oxygens.　Molecular　orbital　analysis　reveals　that　the　Re3　core　in　Re3O　3-　possesses　conflicting　d-orbital　aromaticity　(π-antiaromatic　and　σ-aromatic),　consistent　with　its　C2v　symmetry.　Well-resolved　photodetachment　transitions　from　the　Re　5d　z2　δ　orbitals　allow　the　bond　strength　and　resonance　energy　of　a　delocalized　δ-bond　to　be　estimated.　©　2012　The　Royal　Society　of　Chemistry.