Tl2[B10H10] and Tl2[B12H12]: crystal structures, Raman spectra and Tl+ lone-pair luminescence in comparison

Thallium(I) decahydro-closo-decaborate Tl-2[B10H10] and thallium(I) dodecahydro-closo-dodecaborate Tl-2[B12H12] are readily available as microcrystalline powders from reactions of thallium(I) carbonate Tl-2[CO3] with aqueous solutions of the respective free acid (H3O)(2)[B10H10] or (H3O)(2)[B12H12]. Tl-2[B12H12] crystallizes with an anti-fluorite related structure (cubic, F m 3 <mml:mo stretchy="true">? </mml:mover> , a = 1074.23(8) pm, Z = 4). Each Tl+ cation is coordinated by four icosahedral [B12H12](2-) anions (d(B-B) = 180-181 pm) providing a twelvefold coordination sphere of hydrogen atoms (d(Tl-H) = 296 pm). Tl-2[B10H10] crystallizes monoclinically in the space group P2(1)/n with a = 704.03(5), b = 1111.45(8), c = 1281.16(9) pm and beta = 94.912(3)degrees for Z = 4. The bicapped square antiprismatic [B10H10](2-) anions (d(B-B) = 147-176 pm to the two apical boron atoms, d(B-B) = 161-199 pm within the corpus) again form distorted tetrahedra around the (Tl1)(+), but square pyramids around the (Tl2)(+) cations. Thus (Tl1)(+) is coordinated by 12 hydrogen atoms (d(Tl1-H) = 275-315 pm), but (Tl2)(+) only by 11 of them (d(Tl2-H) = 267-357 pm). Both compounds show a greenish-yellow photoluminescence caused by an interconfigurational 6sp-6s(2) emission (P-3(n)-> S-1(0), n = 0-2) at the Tl+ cation.