Toward Multilayer Architectures in Transition-Metal/Main-Group Cluster Oxides: Ir3Sn12In3O14, Ir2.3Ru1.7Sn19O18 and Ir10Sn45O44A Homologous Series with Progressive Band Condensation

A series of cluster oxides exhibiting a systematic increase in the degree of band condensation was synthesized by the reactive Sn-flux method: Ir3Sn12In3O14 (3-fold band), Ir2.3Ru1.7Sn19O18 (4-fold band), and Ir10Sn45O44 (5-fold band). Single-crystal X-ray diffraction reveals that these compounds crystallize in the noncentrosymmetric polar space groups Cm and Cmc21 and the centrosymmetric space group C2/m, respectively. Polarized second harmonic generation (SHG) measurements corroborate the bulk noncentrosymmetric nature of Ir2.3Ru1.7Sn19O18, whereas no SHG response is detected for centrosymmetric Ir10Sn45O44. The formal oxidation states were determined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS), and electronic band structure calculations reveal semiconducting band gaps consistent with the measured optical properties. Increasing band condensation is accompanied by a color change from red-orange for Ir3Sn12In3O14 to black for Ir10Sn45O44. Ir3Sn12In3O14 exhibits a photoluminescence emission centered at 566 nm (yellow light). These findings establish a homologous family of multilayer transition-metal/main-group cluster oxides with systematically tuneable crystal symmetry, electronic structure, nonlinear optical response, and optical properties.