Ba5Ga4Se10: a new selenidogallate containing the novel [Ga4Se10]10− anionic cluster with Ga in a mixed-valence state

Abstract

The new compound Ba₅Ga₄Se₁₀ has been synthesized for the first time. It crystallizes in the tetragonal space groupI4/mcm with a = 8.752(2) Å, c = 13.971(9) Å, and Z = 2. The structure contains discrete [Ga₄Se₁₀]¹⁰⁻ anions and charge-compensating Ba²⁺ cations. The novel highly anionic [Ga₄Se₁₀]¹⁰⁻cluster is composed of two Ga(Se)₄ tetrahedra and two Ga(Ga)(Se)₃ tetrahedra with Ga in the 2+/3+ valence states. It also exhibits an unusually long Ga–Se distance of 2.705(2) Å, which has only been observed under high pressure conditions before. A band gap of 2.20(2) eV was deduced from the UV/vis diffuse reflectance spectrum.