Extraordinary intense blue Tl+ lone-pair photoluminescence from thallium(I) chloride hydroborate Tl3Cl[B12H12]

Microcrystalline powder of previously unknown thallium(I) chloride hydroborate Tl₃Cl[B₁₂H₁₂] was obtained through the reaction of thallium(I) oxocarbonate Tl₂[CO₃] with an aqueous solution of (H₃O)₂[B₁₂H₁₂] in the presence of chloride anions. Tl₃Cl[B₁₂H₁₂] 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. Tl₃Cl[B₁₂H₁₂] shows strong excitation bands at 240 and 260 nm attributed to the ¹S₀ → ³P₂ and ¹S₀ → ³P₁ interconfigurational transitions of the Tl⁺ 6s² 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 Tl₃Cl[B₁₂H₁₂] were determined.