Extraordinary intense blue Tl + lone-pair photoluminescence from thallium(I) chloride hydroborate Tl 3 Cl[B 12 H 12 ].

Microcrystalline powder of previously unknown thallium(I) chloride hydroborate Tl 3 Cl[B 12 H 12 ] was obtained through the reaction of thallium(I) oxocarbonate Tl 2 [CO 3 ] with an aqueous solution of (H 3 O) 2 [B 12 H 12 ] in the presence of chloride anions. Tl 3 Cl[B 12 H 12 ] crystallises in a primitive, orthorhombic lattice with the space group Pnma ( a = 835.189(7) pm, b = 970.132(8) pm and c = 1597.912(12) pm for Z = 4) showing a distorted hexagonal anti -perovskite type arrangement of the ions. The structure features two thallium sites with mixed coordination spheres consisting of borate related hydrogen atoms and chloride anions with coordination numbers of eleven and thirteen. Tl 3 Cl[B 12 H 12 ] shows strong excitation bands at 240 and 260 nm attributed to the 1 S 0 → 3 P 2 and 1 S 0 → 3 P 1 interconfigurational transitions of the Tl + 6s 2 cations, respectively. The emission spectrum at 300 K upon VUV excitation exhibits a broad band at 440 nm with a quantum efficiency of 41%. In addition, temperature-dependent emission spectra, colour points, reflectance, decay time, thermal quenching curve and radioluminescence spectra for Tl 3 Cl[B 12 H 12 ] were determined.