Synthesis and Characterization of Cs₄ Ga₆ Q₁₁ (Q=S, Se): Chalcogenometalates with Exotic Polymeric Anions

Two new chalcogenogallates Cs₄ Ga₆ Q₁₁ (Q=S, Se) were obtained by a controlled thermal treatment of CsN₃ in the presence of stoichiometric amounts of Ga₂ Q₃ and the elemental chalcogens at elevates temperatures. Both isotypic compounds crystallize in the space group P $$ (no. 2). The most prominent structural feature in these chalcogenogallates are the complex anionic Dreier double chains $$ [Ga₆ Q₁₁ ^4- ] formed by condensed GaQ₄ tetrahedra. The semiconductors Cs₄ Ga₆ S₁₁ (E_g =3.14 eV) and Cs₄ Ga₆ Se₁₁ (E_g =2.41 eV) were further studied by using UV/Vis, ¹³³ Cs and ⁷¹ Ga solid-state NMR spectroscopy, and complementary DFT calculations. The ¹³³ Cs MAS NMR spectra are characteristic for cationic cesium and vibrational spectra show two distinct regions, attributed to the Ga-Q valence and deformation vibrations, respectively. High-temperature studies revealed incongruent melting of both solids, which is also depicted in updated binary phase-diagrams Cs₂ Q-Ga₂ Q₃ (Q=S, Se).