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

Four new metal chalcogenides containing fluorine, Na2Ba17In8Q21F18 (Q = S, Se), KBa2InQ3F2 (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, Na2Ba17In8Q21F18 (Q = S, Se), KBa2InQ3F2 (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 KBa2InSe3F2 and Na2Ba17In8Se21F18 have relatively large birefringences (0.096 and 0.083 at 532 nm, respectively), which are larger than that of KBa2InS3F2(0.056 @ 532 nm) and Na2Ba17In8S21F18 (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 InQn (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 MIII/cation ratios on the polymerization of In–Q (Q=S, Se) units have been discussed.