Syntheses, structures, and characterization of new heteroanionic chalcohalides: Na2Ba17In8Q21F18 (Q = S, Se), KBa2InQ3F2 (Q = S, Se)

Four new metal chalcogenides containing fluorine, Na 2 Ba 17 In 8 Q 21 F 18 (Q = S, Se), KBa 2 InQ 3 F 2 (Q = S, Se) were synthesized by the solid-state reactions, and their structures were determined by single crystal X-ray diffraction. To the best of our knowledge, they represent the first example of F-containing mixed alkali and alkaline earth In-based chalcogenides . Structurally, Na 2 Ba 17 In 8 Q 21 F 18 (Q = S, Se), KBa 2 InQ 3 F 2 (Q = S, Se) all feature one-dimensional chain-like structures composed of In-based polyhedra, but they are not isostructural. The optical property measurements indicate that KBa 2 InSe 3 F 2 and Na 2 Ba 17 In 8 Se 21 F 18 have relatively large birefringences (0.096 and 0.083 at 532 nm, respectively), which are larger than that of KBa 2 InS 3 F 2 (0.056 @ 532 nm) and Na 2 Ba 17 In 8 S 21 F 18 (0.041 @ 532 nm). Their structure-property relationship demonstrates that the large difference of birefringence among these compounds mainly arises from the different connection modes of InQ n (n = 4, 5) polyhedra. In addition, the first-principles calculations, UV–vis–NIR diffuse reflectance spectra and IR spectroscopy of title compounds have also been performed. The effect of M III /cation ratios on the polymerization of In–Q (Q=S, Se) units have been discussed.