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 (Eg), 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 Eg appears to be close to linear for all studied compounds.