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The present study investigates the crystal structures, Raman spectra, and Tl+-lone-pair luminescence of Tl2[B10H10] and Tl2[B12H12]. It is found that salts with dodecahydro-closo-dodecaborate dianions [B12H12]2- often form hydrated structures, while salts with heavy alkali metals A2[B12H12] are generally anhydrous. The structural, vibrational spectroscopic, and luminescence properties of the anhydrous decahydro- and dodecahydro-closo-borates of thallium are compared with Tl2[B10H10]. The study shows that Tl2[B10H10] crystallizes in the monoclinic space group P21/n and is isotypic with the alkali metal decahydro-closo-decaborates A2[B10H10] (A = Na-Rb). Table 1 contains crystallographic data for Tl2[B10H10]. The molecule has a monoclinic crystal system and a space group of P2₁/n. The lattice parameters are a = 704.03 pm, b = 1111.45 pm, c = 1281.16 pm, and β = 94.912°. The calculated density is 3.50 g/cm³ and the molar volume is 150.38 cm³/mol. Table 2 shows the positional and equivalent isotropic displacement parameters for Tl2[B10H10]. The decahydro-closo-decaborate dianion [B10H10]2– consists of ten crystallographically distinct boron and hydrogen atoms that form the B10-closo cage. The B–B distances vary between 147 and 199 pm, depending on the position of the boron atoms in the cage. The distortion of the cage is caused by the thallium(I) cation and the ionic radius of the cation. The crystal structures of Tl2[B10H10] and Tl2[B12H12] were investigated. In Tl2[B10H10], the [B10H10]2– anion forms a hexagonal closest packing, with the tetrahedral voids filled with (Tl1)+ cations and the octahedral voids filled with (Tl2)+ cations. The coordination environment of the thallium(I) cations exhibits a tetrahedral and a square pyramidal structure. In Tl2[B12H12], a cubic closest packing of [B12H12]2– anions is present, with the Tl+ cations occupying the tetrahedral voids. The Raman spectra of both compounds exhibit similar bands. The Raman spectra of Tl2[B12H12] and Tl2[B10H10] show sharp double bands in the B–H vibration range. In the range of 1100 to 400 cm−1, the symmetric breathing vibrations of the boron cages can be clearly assigned. Both compounds exhibit yellow-green photoluminescence with a broad emission band at 510 and 522 nm, respectively. The luminescence appears greenish to yellowish-white. The emission spectra are caused by the transition 3P1→1S0 of Tl+. The excitation spectrum of Tl2[B10H10] shows two bands at 332 and 255 nm, while the excitation spectrum of Tl2[B12H12] exhibits three bands at 360, 330, and 263 nm. The structure of Tl2[B10H10] consists of a hexagonal closest packing, while Tl2[B12H12] is in a [Extracted from the article]

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