Synthesis, Crystal Structure, and Optical Properties of Layered Perovskite Scandium Oxychlorides: Sr2ScO3Cl, Sr3Sc2O5Cl2, and Ba3Sc2O5Cl2

We report the successful synthesis of three new Ruddlesden–​Popper-type scandium oxychloride perovskites, Sr2Sc­O3Cl, Sr3Sc2­O5Cl2, and Ba3Sc2­O5Cl2, by conventional solid-state reaction. Small single crystals of Sr2Sc­O3Cl were obtained by a self-flux method, and the crystal structure was determined to belong to the tetragonal P4/nmm space group (a = 4.08066(14) Å, c = 14.1115(8) Å) by X-ray diffraction analysis. The scandium center forms a ScO5Cl octahedron with ordered apical oxygen and chlorine anions. The scandium cation, however, is shifted from the position of the octahedral center toward the apical oxygen anion, such that the coordination geometry of the Sc cation can be effectively viewed as an ScO5 pyramid. These structural features in the oxychloride are different from those of octahedral ScO5F coordinated with a partial O/F anion order at the apical sites in the oxyfluoride Sr2Sc­O3F. Rietveld refinements of the neutron powder diffraction data of Sr3Sc2­O5Cl2 (I4/mmm: a = 4.107982(5) Å, c = 23.58454(7) Å) and Ba3Sc2­O5Cl2 (I4/mmm: a = 4.206920(5) Å, c = 24.54386(6) Å) reveal the presence of pseudo ScO5 pyramids with the Cl anion being distant from the scandium cation, which is similar to the Sc-centered coordination geometry in Sr2Sc­O3Cl with the exception that the ScO5 pyramids form double layers by sharing the apical oxygen. Density functional calculations on Sr2Sc­O3Cl indicate the strong covalency of the Sc–O bonds but almost nonbonding interaction between Sc and Cl ions.