Homo- and heterometallic iodobismuthates(III) with 1,3,5-trimethylpyridinium cation: preparation and features of optical behavior

Ternary Complexes of BiI3/CuI and SbI3/CuI with Tetrahydrothiophene

Reactions of BiI3/CuI mixtures with tetrahydrothiophene (THT) in toluene produce 2-D sheet networks BiCu3I6(THT)n (n = 2, 3, or 4), depending on reaction conditions. All three structures are based on BiI6 octahedra, which share pairs of (μ2-I)2 with Cu3(THT)n units. BiCu3I6(THT)2 features Cu2(μ2-I)2 rhombs with close Cu···Cu interactions and is accompanied by formation of the very complex HBi3Cu12I22(THT)8. Reactions of SbI3/CuI with THT in toluene produced a SbCu3I6(THT)2 network shows Cu3(μ2-THT)2 units, like its Bi congener, but Cu6(μ2-I)6 barrels rather than rhombs. Isolated SbI3 units are stacked above the Cu6I6 barrels. A molecular compound, Sb3Cu3I12(THT)6 consists of a face-sharing Sb3I12 stack, in which the Cu-THT units are bonded in asymmetric fashion about the central SbI6. Metal-halide bonds were investigated via QTAIM and NLMO analyses, demonstrating that these bonds are largely ionic and occur between the Bi/Sb and I p orbitals. Hirshfeld analysis shows significant H···H and H···I interactions. Diffuse reflectance spectroscopy (DRS) reveals band edges for the Bi species of 1.71-1.82 eV, while those for the neutral Sb complexes are in the range of 1.94-2.06 eV. Mapping of the electronic structure via density of state calculations indicates population of antibonding Bi/Sb-I orbitals in the excited state.

Copper- and Silver-Containing Heterometallic Iodobismuthates: Features of Thermochromic Behavior

Nine heterometallic iodobismuthates with the general formula Cat₂{[Bi₂M₂I₁₀}] (M = Cu(I), Ag(I), Cat = organic cation) were synthesized. According to X-ray diffraction data, their crystal structures consisted of {Bi₂I₁₀} units interconnected with Cu(I) or Ag(I) atoms through I-bridging ligands, forming one-dimensional polymers. The compounds are thermally stable up to 200 °C. Optical band gaps (E_g), estimated at room temperature via diffuse reflectance measurements, range from 1.81 to 2.03 eV. Thermally induced changes in optical behavior (thermochromism) for compounds 1-9 were recorded, and general correlations were established. The thermal dependence of E_g appears to be close to linear for all studied compounds.

[SMe3]2[Bi2Ag2I10], a silver iodido bismuthate with an unusually small band gap

Iodido metalates of heavy main group elements have seen much research interest in the last years due to their possible application as absorbers in photovoltaics. However, for materials based on the non-toxic element bismuth one challenge lies in narrowing the optical band gap for sufficient solar absorption. Here, we present a new iodido silver bismuthate, [SMe₃]₂[Bi₂Ag₂I₁₀] (1), which is prepared from solution and characterized regarding its structure, thermal stability and optical absorption. While compounds with similar anion compositions are known, the band gap of 1.82 eV is the smallest in chain-like Bi/Ag/I-compounds that has been reported to date. To support our experimental findings we carried out computational investigations and were able to reproduce the surprisingly narrow band gap, highlighting the subtle influence of the connectivity of different building units in multinary bismuthates. We also prepared and characterized the simple iodido pentelates [SMe]₃[E₂I₉] (E = Bi, Sb; 2, 3) to provide a point of comparison.