Synthesis, crystal structure and optical properties of the first Hg-based polyselenide Ba2HgSe5

A new polyselenide, Ba 2 HgSe 5 has been synthesized via conventional high-temperature solid state reaction . Single-crystal X-ray diffraction experiment reveals that the title compound crystallizes in the centrosymmetric space group Pnma of the orthorhombic system with a  = 12.7123(7) Å, b  = 8.9593(5) Å, c  = 8.5470(5) Å and Z  = 4. Its crystal structure consists of isolated dumbbell-shaped (HgSe 2 ) 2- and V-shaped Se 3 2− ions. These molecular anions are charge-balanced by Ba 2+ . Diffuse reflectance spectrum demonstrates the semiconducting properties with a direct band gap of 1.75 eV. Electronic band structure calculation indicates that the band gap is defined by the 4 p -orbitals of the selenium atoms of the Se 3 2− groups. Moreover, the photocatalytic behavior of the polycrystalline sample was investigated by decomposing antibiotics tetracycline hydrochloride under visible right irradiation and the result indicates that the title compound displays moderate degradation rate of 60 % within 2 h. In addition, thermal analysis shows that Ba 2 HgSe 5 has a good thermal stability up to 640 °C and exhibits incongruent melting behavior. These characteristics imply that Ba 2 HgSe 5 may be a fascinating photoelectronic material and has potential applications in the future.