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 1 ‾ (no. 2). The most prominent structural feature in these chalcogenogallates are the complex anionic Dreier double chains 1 ∞ [Ga6 Q11 4- ] formed by condensed GaQ4 tetrahedra. The semiconductors Cs4 Ga6 S11 (Eg =3.14 eV) and Cs4 Ga6 Se11 (Eg =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).