Sn_4-δB₁₂Se₁₂[Q_x], Q = Se, Te, a B₁₂Cluster Tunnel Framework Hosting Neutral Chalcogen Chains

We report the open framework semiconductor, Sn4B12Se12, synthesized using a Sn/Se flux method. The framework in this compound features the rare icosahedral [B12Se12]14- anion assembled into a 3D tunnel structure with open tunnels and is chemically stable over a wide pH range from concentrated nitric acid to 3 M NaOH aqueous solution. The rigid nature of this structure and high chemical stability allows chemical strategies for the removal of Se chains from the tunnels, giving an empty tunnel structure and subsequent insertion of tellurium chains as confirmed through single-crystal X-ray diffraction. The as-synthesized Sn4B12Se12[Se3.80] contains selenium chains in the tunnels and crystallizes in the hexagonal space group P6322 with a = b = 13.5927(7) Å, c = 9.8167(5) Å. After removal of Se and subsequent Te insertion, the space group remains the same with small changes in lattice parameters and occupancy of tin sites. The experimentally obtained optical band gap of the as-synthesized material is 1.66 eV and can be modulated by chemical modifications. DFT calculations of the empty framework show an indirect nature of the band gap calculated at 1.16 eV. The neutral framework of Sn4B12Se12 is a new example of a microporous semiconductor with exceptional stability and electronic properties that stem from the presence of icosahedral boron clusters.