Thermolysis of Cs9MO4 (M = In, Sc): Synthesis, Crystal Structure, Chemical Bonding, and Reactivity of the Subvalent Oxidometalates Cs7MO4 (M = In, Sc)

The cesium-poor alkali-metal suboxidometalates Cs7MO4 (M = In, Sc) were prepared from the respective cesium-rich suboxidometalates Cs9MO4 by thermolysis in a dynamic vacuum at temperatures below 150 °C. They crystallize in a new structure type, comprising isolated tetrahedral oxidometalate anions [MO4]5- immersed in a matrix of metallic cesium atoms. This structural separation into alternating ionic and metallic building units is typical for subvalent compounds. Cs7InO4 and Cs7ScO4 are isotypic and form mixed crystals Cs7(In1-xScx)O4 with statistic distribution of In and Sc atoms. All compounds were characterized by single crystal and powder X-ray diffraction. Calculations of the electronic structure with DFT methods corroborate the coexistence of anionic entities within a metallic matrix and give evidence of the subvalent nature of cesium atoms. Overall metallic behavior is a consequence of the equal volume fractions of metallic and ionic regions, allowing for percolation of the conduction electrons throughout the crystal volume. Differential thermoanalysis was employed to gain insight into the chemical conversion processes during the thermolysis reaction. The thermolytic decomposition of Cs9MO4 is a multistep process with, in some instances, reversible amorphization and recrystallization steps. Finally, the formation of ionic compounds is observed. The full decomposition of Cs9ScO4 yields the two new oxidoscandates Cs14Sc4O13 and Cs17Sc5O15 with tetrahedral [ScO4] units connected to chain fragments and the indium compound yields cesium oxidoindates with low-condensed [InO4] building units. The cesium-poor suboxidometalates Cs7MO4 themselves can serve as starting materials for the synthesis of further, new suboxidometalates, as they show a unique reactivity toward metals.

Infrared Spectra and Density Functional Calculations for the Sc(OH)2,3 and HOScO Molecules and the Sc(OH)2+ Cation in Solid Argon

Reactions of laser-ablated Sc atoms with H2O2 molecules or H2 and O2 mixtures in excess solid argon gives four major new products, which are identified from concentration dependence, isotopic substitution, the effect of electron trap doping, and comparison to frequencies calculated by the B3LYP density functional. These are the Sc(OH)3 trihydroxide, the Sc(OH)2 dihydroxide, the Sc(OH)2+ cation, and the trihydroxide anhydride HOScO molecule. The Sc(OH)2+ cation forms a complex in solid argon that is effectively modeled by calculations for the [(Ar)4Sc(OH)2]+ cation including frequency shifts between the neutral and cation dihydroxides. Finally, the Sc(OH)4- anion is detected in H2O2 experiments.