Photoluminescent Properties of Chalcobromide-capped Octahedral Hexarhenium(III) Complexes [{Re6Q8-nBrn}Br6]n-4 (Q = Se, n=1-3; Q = S, n=1, 2)

Photoluminescent properties of chalcobromide-capped octahedral hexarhenium(III) complexes with terminal bromide ligands [{Re(6)Q(8-n)Br(n)}Br-6](n-4) (Q = Se, n = 1 ([1-Se](3-)), n = 2 ([2a-Se](2-) and [2b-Se](2-)), and n=3 ([3-Se](-)); Q = S, n = 1 ([1-S](3-)), n = 2 ([2a-S](2-), [2b-S](2-), and [2c-S](2-)) were studied. The Q(7)Br capped complex [{Re(6)Q(7)Br}Br-6](3-) and Q(6)Br(2) [{Re(6)Q(6)Br(2)}Br-6](2-) (both D-3d and C-2 nu symmetric geometrical isomers) were successfully separated by column chromatography. All of the chalcobromide-capped complexes studied showed photoluminescence in both crystalline and solution phases. The emission maximum wavelength of the complexes at 296 K spans 853-915 or 868-968 nm in the crystalline phase or in acetonitrile, respectively. The selenobromide-capped complexes showed more intense emission as compared with the thiobromide analogues. The emission quantum yield (Phi(em)) and emission lifetime (tau(em)) became smaller and shorter, respectively, with an increase in the number of a capping bromide ligand in [{Re(6)Q(8-n)Br(n)}-Br-6](n-4). In the crystalline phase at 80 K, the emission maximum of the chalcobromide-capped complex shifted to the longer wavelength relative to that at 296 K. The emissive excited-state of the chalcobromide-capped hexarhenium(III) complexes was concluded to originate from the {Re(6)Q(8-n)Br(n)}(n+2) core with a spin-triplet type. The Phi(em) and tau(em) values of the {Re(6)Q(8-n)Br(n)}(n+2) complex were dependent significantly on the symmetry of the hexarhenium core, showing more intense emission for the complex with the higher symmetric core. A linear correlation between natural logarithm of the nonradiative decay rate constant and the emission maximum energy was observed for [{Re(6)Q(6)Br(2)}Br-6](2-).