| Summary: | Tl[CB<sub>11</sub>H<sub>12</sub>] was prepared with a reaction of Tl<sub>2</sub>[CO<sub>3</sub>] with the acid of the monocarba-<i>closo</i>-dodecaborate anion (H<sub>3</sub>O)[CB<sub>11</sub>H<sub>12</sub>] in aqueous solution as prismatic colorless single crystals by isothermal evaporation from the clear brine. It crystallizes in a monoclinic primitive structure with the space group <i>P</i>2<sub>1</sub>/<i>c</i> (<i>a</i> = 685.64(3) pm, <i>b</i> = 1978.21(9) pm, <i>c</i> = 1006.89(5) pm, <i>β</i> = 132.918(3)° for <i>Z</i> = 4), which can be derived from the halite-type arrangement if the <i>closo</i>-carbaborate cages are considered as spheres. Due to the different atoms in the [CB<sub>11</sub>H<sub>12</sub>]<sup>−</sup> anion, Tl[CB<sub>11</sub>H<sub>12</sub>] features interesting C–H<sup>δ+</sup> ∙∙∙ <sup>δ−</sup>H–B interactions near to non-classical hydrogen bridges (“dihydrogen bonds”) and exhibits considerably different luminescence properties compared to regular <i>closo</i>-hydroborates, such as Tl<sub>2</sub>[B<sub>10</sub>H<sub>10</sub>], Tl<sub>2</sub>[B<sub>12</sub>H<sub>12</sub>] and Tl<sub>3</sub>Cl[B<sub>12</sub>H<sub>12</sub>]. Tl[CB<sub>11</sub>H<sub>12</sub>] shows strong photoluminescence (PL) at 390 nm, while the excitation bands for this broad band are located at 245 and 280 nm. It is caused by an interconfigurational [Xe]4f<sup>14</sup>5d<sup>10</sup>6s<sup>2</sup> (<sup>3</sup>P<sub>1</sub>) to [Xe]4f<sup>14</sup>5d<sup>10</sup>6s<sup>1</sup>6p<sup>1</sup> (<sup>1</sup>S<sub>0</sub>) transition, which is also known as lone-pair luminescence. The quantum yield is rather low (<10 %), which is likely caused by the rather large Stokes shift. In addition, temperature-dependent emission spectra were recorded to determine the thermal quenching curve and the respective quenching temperature.
|
|---|