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

A new polyselenide, Ba2HgSe5 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) angstrom, b = 8.9593(5) angstrom, c = 8.5470(5) angstrom and Z = 4. Its crystal structure consists of isolated dumbbell-shaped (HgSe2)2- and V-shaped Se32- ions. These molecular anions are charge-balanced by Ba2+. 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 4p-orbitals of the selenium atoms of the Se32- 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 Ba2HgSe5 has a good thermal stability up to 640 degrees C and exhibits incongruent melting behavior. These characteristics imply that Ba2HgSe5 may be a fascinating photoelectronic material and has potential applications in the future.