Ionothermal synthesis of discrete supertetrahedral Tn (n=4, 5) clusters with tunable components, band gaps, and fluorescence properties

The preparation of crystalline molecularly supertetrahedral Tn clusters with variable sizes and components is of vital importance for the fundamental study of their physicochemical properties. However, setting up an efficient method to stabilize large discrete Tn clusters is a challenge due to their high negative charges and polymerization nature. In this work, we report on the ionothermal synthesis of three discrete T4 cluster compounds, namely [Bmmim] 5[(CH3)(2)NH2](4)[NH4][M4In16S31(SH)(4)]center dot 6H(2)O (M = Mn (1), Zn (2), Cd (3), Bmmim = 1-buty-2,3-dimethyl-imidazolium), and four discrete T5 cluster compounds, namely [Bmmim](10)[NH4](3)[Cu5Ga30-xInxS52(SH)(4)] (x = 6.6 (5), 14.5 (6), 23.8 (7), and 30 (8)). The compound [Bmmim](10)[NH4](3)[Cu5Ga30S52(SH)(4)] (4) previously reported by us features a discrete T5 cluster. The steep UV-Vis absorption edges indicate band gaps of 2.20 eV for 1, 2.64 eV for 2, 2.69 eV for 3, 3.04 eV for 4, 2.65 eV for 5, 2.48 eV for 6, 2.32 eV for 7, and 2.30 eV for 8. The compositions of T5 clusters could be varied with the ratios of Ga : In in the starting reagents, providing an opportunity to systematically control the band gaps and fluorescence performances of T5 cluster-based compounds. This research might advance the understanding of the ionothermal preparation and functionality tuning of crystalline chalcogenides.