The crystal structure of RbI3 and TlI3

Orthorhomic, Pnma Z=4, λ(MoKα)=0.71069 A, T=300 K. RbI3: Mr=466.18, a=10.908 (1), b=6.655 (1), c=9.711 (1) A, V=704.96 A3, Dx4.392 Mg m-3, μ(MoKα)=19.71 mm-1, F(000)=784. T1I3: Mr=585.10, a=10.599 (2), b=6.419 (2), c=9.436 (2) A, V=641.98 A3, Dx=6.053 Mg m-3, μ(MoKα)=39.55 mm-1, F(000)=960. The crystal structures are isotypic with CsI3 and have been refined by full-matrix least squares to RF=0.027 for 727 reflections of RbI3 and to RF=0.042 and 410 relections of TiI3 [I≤3σ(I)]. The triiodide ions I3- are asymmetrical and slighlty bent with d=2.833 (1), 3.051 (1) A, φ=178.11 (3)0 for RbI3 and d=2.826 (3), 3.063 (3) A, φ=177.89 (9)0 for TiI3. The asymmetry of the triiodide ion as a function of the size of the cations is discussed for the four isotypic compounds MI3, M=Tl, Rb, Cs, NH4. (orig.)