Discrete Ru(Sn)<sub>6</sub> Octahedra Encapsulated\nin Oxoindate Channels: RuSn<sub>6</sub>In<sub>6</sub>O<sub>16</sub> with Highly Ordered In/Sn Sites

A new transition metal–mixed main group element\ncluster\ncompound, RuSn<sub>6</sub>In<sub>6</sub>O<sub>16</sub>, was prepared\nvia the tin-flux method. Single-crystal structure refinements show\nthat RuSn<sub>6</sub>In<sub>6</sub>O<sub>16</sub> crystallizes in\na monoclinic crystal system with a centrosymmetric <i>C</i>2/<i>m</i> space group. It shows a unique structure type\nreminiscent of metal–organic framework (MOF) structures. The\nstructure exhibits a highly positive [Ru(Sn)<sub>6</sub>]<sup>14+</sup> metallic cluster (guest) encapsulated in an oxoindate framework\n(host) formed by a combination of corner- and edge-sharing InO<sub>6</sub>/InO<sub>7</sub> polyhedra. The oxidation states were experimentally\nand theoretically determined to be Ru<sup>2+</sup> and Sn<sup>2+</sup> in the metallic cluster and In<sup>3+</sup> in the oxide layers.\nThe cluster shows a direct band gap like that of semiconducting materials,\nwhich was also confirmed by band structure calculations. The photoluminescence\nspectrum exhibits a peak at 455 nm (blue emission), which may originate\nfrom oxygen vacancies in the microcrystalline powder. This indicates\nthat RuSn<sub>6</sub>In<sub>6</sub>O<sub>16</sub> has the potential\nto be used in light-emitting diodes (LEDs) and photovoltaic applications.