Thermolysis of Cs<sub>9</sub><i>M</i>O<sub>4</sub> (<i>M</i> = In,\nSc): Synthesis, Crystal Structure,\nChemical Bonding, and Reactivity of the Subvalent Oxidometalates Cs<sub>7</sub><i&g

The cesium-poor alkali-metal suboxidometalates Cs<sub>7</sub><i>M</i>O<sub>4</sub> (<i>M</i> = In,\nSc) were prepared\nfrom the respective cesium-rich suboxidometalates Cs<sub>9</sub><i>M</i>O<sub>4</sub> by thermolysis in a dynamic vacuum at temperatures\nbelow 150 °C. They crystallize in a new structure type, comprising\nisolated tetrahedral oxidometalate anions [<i>M</i>O<sub>4</sub>]<sup>5–</sup> immersed in a matrix of metallic cesium\natoms. This structural separation into alternating ionic and metallic\nbuilding units is typical for subvalent compounds. Cs<sub>7</sub>InO<sub>4</sub> and Cs<sub>7</sub>ScO<sub>4</sub> are isotypic and form mixed\ncrystals Cs<sub>7</sub>(In<sub>1–<i>x</i></sub>Sc<sub><i>x</i></sub>)O<sub>4</sub> with statistic distribution\nof In and Sc atoms. All compounds were characterized by single crystal\nand powder X-ray diffraction. Calculations of the electronic structure\nwith DFT methods corroborate the coexistence of anionic entities within\na metallic matrix and give evidence of the subvalent nature of cesium\natoms. Overall metallic behavior is a consequence of the equal volume\nfractions of metallic and ionic regions, allowing for percolation\nof the conduction electrons throughout the crystal volume. Differential\nthermoanalysis was employed to gain insight into the chemical conversion\nprocesses during the thermolysis reaction. The thermolytic decomposition\nof Cs<sub>9</sub><i>M</i>O<sub>4</sub> is a multistep process\nwith, in some instances, reversible amorphization and recrystallization\nsteps. Finally, the formation of ionic compounds is observed. The\nfull decomposition of Cs<sub>9</sub>ScO<sub>4</sub> yields the two\nnew oxidoscandates Cs<sub>14</sub>Sc<sub>4</sub>O<sub>13</sub> and\nCs<sub>17</sub>Sc<sub>5</sub>O<sub>15</sub> with tetrahedral [ScO<sub>4</sub>] units connected to chain fragments and the indium compound\nyields cesium oxidoindates with low-condensed [InO<sub>4</sub>] building\nunits. The cesium-poor suboxidometalates Cs<sub>7</sub><i>M</i>O<sub>4</sub> themselves can serve as starting materials for the\nsynthesis of further, new suboxidometalates, as they show a unique\nreactivity toward metals.