Photoluminescent Re₆Q₈I₂ (Q = S, Se) Semiconducting Cluster Compounds

We report three new rhenium chalcohalide cluster compounds, Re6S8I2, Re6S4Se4I2, and Re6Se8I2. The materials crystallize in the three-dimensional (3D) Re6S8Cl2 structure type with the space group P21/n. They can be synthesized with sufficiently large iodine gas pressures or using alkali metal iodide salt fluxes with excess iodine. All three compounds are thermally stable under vacuum up to 1000 °C, and density functional theory (DFT) calculation results predict them to be direct-gap semiconductors. The measured work functions, which are the valence band maxima with respect to vacuum, and the measured band gaps are 5.49(5) and 1.69(5) eV, 5.24(5) and 1.54(5) eV, and 5.03(5) and 1.44(5) eV for Re6S8I2, Re6S4Se4I2, and Re6Se8I2, respectively. They exhibit red to near-IR photoluminescence ranging from 1.38 eV (898 nm) to 1.93 eV (642 nm) centered at 1.67 eV (742 nm) for Re6S8I2 and ranging from 1.35 eV (918 nm) to 1.70 eV (726 nm) centered at 1.49 eV (832 nm) for Re6Se8I2 with average lifetimes of 5.15 and 1.83 ns, respectively.