NaBaMIIIQ3 (MIII = Al, Ga; Q = S, Se): first quaternary chalcogenides with isolated edge-sharing (MIII2Q6)6− dimersElectronic supplementary information (ESI) available: Cif, synthesis, experimental detail, structural refinement and crystal data, electronic structures, optical properties and PDOS. CCDC 1856544, 1856545, 1856546, 1856547 for NaBaAlS3, NaBaAlSe3, NaBaGaS3 and NaBaGaSe3, respectively. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt04048f

In this study, a new series of NaBaM III Q 3 (M III = Al, Ga; Q = S, Se) compounds featuring the first discovered isolated edge-shared (M III 2 Q 6 ) 6− dimers in known quaternary chalcogenides were synthesized. All compounds showed clear optical anisotropy (Δ n = 0.04-0.12) mainly derived from the contribution of isolated (M III 2 Q 6 ) 6− dimers by the real-space atom-cutting method. New series of quaternary chalcogenides with firstly discovered isolated edge-sharing (M III 2 Q 6 ) 6− dimers showing obvious optical anisotropy were reported.