Synthesis, Crystal Structure, and Optical Properties of Layered Perovskite Scandium Oxychlorides: Sr<sub>2</sub>ScO<sub>3</sub>Cl, Sr<sub>3</sub>Sc<sub>2</sub>O<sub>5</sub>Cl<sub>2</sub>, and Ba<sub>3</sub>Sc<sub>2</sub>O<sub>5</sub>Cl<sub>2</sub>

We report the successful synthesis of three new Ruddlesden–​Popper-type scandium oxychloride perovskites, Sr<sub>2</sub>Sc­O<sub>3</sub>Cl, Sr<sub>3</sub>Sc<sub>2</sub>­O<sub>5</sub>Cl<sub>2</sub>, and Ba<sub>3</sub>Sc<sub>2</sub>­O<sub>5</sub>Cl<sub>2</sub>, by conventional solid-state reaction. Small single crystals of Sr<sub>2</sub>Sc­O<sub>3</sub>Cl were obtained by a self-flux method, and the crystal structure was determined to belong to the tetragonal <i>P</i>4/<i>nmm</i> space group (<i>a</i> = 4.08066(14) Å, <i>c</i> = 14.1115(8) Å) by X-ray diffraction analysis. The scandium center forms a ScO<sub>5</sub>Cl 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 ScO<sub>5</sub> pyramid. These structural features in the oxychloride are different from those of octahedral ScO<sub>5</sub>F coordinated with a partial O/F anion order at the apical sites in the oxyfluoride Sr<sub>2</sub>Sc­O<sub>3</sub>F. Rietveld refinements of the neutron powder diffraction data of Sr<sub>3</sub>Sc<sub>2</sub>­O<sub>5</sub>Cl<sub>2</sub> (<i>I</i>4/<i>mmm</i>: <i>a</i> = 4.107982(5) Å, <i>c</i> = 23.58454(7) Å) and Ba<sub>3</sub>Sc<sub>2</sub>­O<sub>5</sub>Cl<sub>2</sub> (<i>I</i>4/<i>mmm</i>: <i>a</i> = 4.206920(5) Å, <i>c</i> = 24.54386(6) Å) reveal the presence of pseudo ScO<sub>5</sub> pyramids with the Cl anion being distant from the scandium cation, which is similar to the Sc-centered coordination geometry in Sr<sub>2</sub>Sc­O<sub>3</sub>Cl with the exception that the ScO<sub>5</sub> pyramids form double layers by sharing the apical oxygen. Density functional calculations on Sr<sub>2</sub>Sc­O<sub>3</sub>Cl indicate the strong covalency of the Sc–O bonds but almost nonbonding interaction between Sc and Cl ions.