Ba_5Ga_4Se_(10): A new selenidogallate containing the novel [Ga_4Se_(10)]~(10-) anionic cluster with Ga in a mixed-valence state

摘要

The new compound Ba_5Ga_4Se_(10) has been synthesized for the first time. It crystallizes in the tetragonal space group I4/mcm with a = 8.752(2) ?, c = 13.971(9) ?, and Z = 2. The structure contains discrete [Ga_4Se_(10)]~(10-) anions and charge-compensating Ba~(2+) cations. The novel highly anionic [Ga_4Se_(10)]~(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) ?, 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.