Synthesis and characterization of Cs₄Ga₆Q₁₁ (Q=S, Se). Chalcogenometalates with exotic polymeric anions

Two new chalcogenogallates Cs₄Ga₆Q₁₁ (Q=S, Se) were obtained by a controlled thermal treatment of CsN₃ in the presence of stoichiometric amounts of Ga₂Q₃ and the elemental chalcogens at elevates temperatures. Both isotypic compounds crystallize in the space group P anti 1 (no. 2). The most prominent structural feature in these chalcogenogallates are the complex anionic Dreier double chains ¹_∞[Ga₆Q₁₁^4-] formed by condensed GaQ₄ tetrahedra. The semiconductors Cs₄Ga₆S₁₁ (E_g=3.14 eV) and Cs₄Ga₆Se₁₁ (E_g=2.41 eV) were further studied by using UV/Vis, ¹³³Cs and ⁷¹Ga solid-state NMR spectroscopy, and complementary DFT calculations. The ¹³³Cs 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 Cs₂Q-Ga₂Q₃ (Q=S, Se). (copyright 2018 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)