Synthesis and characterization of new quaternary polyselenide Ba₄TMSbSe₁₂ (TM = Nb, Ta)

Two new quaternary polyselenides, Ba₄TMSbSe₁₂ (TM = Nb, Ta), are synthesized using a solid state reaction. They crystallize in a new structural type with a P-1 triclinic space group, characterized according to single-crystal X-ray diffraction. The structure is alternately stacked using isolated NbSe₉ ⁵⁻ and SbSe₃ ³⁻, which are separated by Ba²⁺. The structure contains the NbSe₉ ⁵⁻ unit with a bipentagonal pyramidal shape coordinated with Se²⁻ and Se₂ ²⁻ in monodenteate and bidentate modes. The vibrational property of the diselenide Se₂ ²⁻ unit was studied using Raman spectrum analysis. ultraviolet–visible diffused reflectance and temperature-dependent resistivity measurements indicate semiconductor behaviors. Calculations of electronic structures indicate the presence of a band gap and strong Se-Se interactions in the diselenide group, which experimentally supports the measured physical properties.