| Abstract
| - A new phase [PtIn6](GeO4)2O, a filled variant of [PtIn6](GaO4)2, and the solid solution[PtIn6](GaO4)2-x(GeO4)xOx/2 (0 ≤ x ≤ 2) were prepared and characterized. Single-crystal structurerefinements show that [PtIn6](GeO4)2O is isotypic with the mineral, sulfohalite Na6FCl(SO4)2, and crystallizesin the space group Fm3̄m (Z = 4) with a = 1006.0(1) pm. The building units of [PtIn6](GeO4)2O are isolated[PtIn6]10+ octahedra and (GeO4)4- tetrahedra, and the isolated O2- ions occupy the centers of the In6octahedra made up of six adjacent PtIn6 octahedra. The lattice parameter of the solid solution[PtIn6](GaO4)2-x(GeO4)xOx/2 (0 ≤ x ≤ 2) varies gradually from a = 1001.3(1) pm at x = 0 to a = 1006.0(1)pm at x = 2, and the color of the solid solution changes gradually from black (x = 0) to red (x = 1) to yellow(x = 2). The cause for the gradual color change was examined by performing density functional theoryelectronic structure calculations for the end members [PtIn6](GaO4)2 and [PtIn6](GeO4)2O. Our analysisindicates that an oxygen atom at the center of a In6 octahedron cuts the In 5p/In 5p bonding interactionsbetween adjacent [PtIn6]10+ octahedra thereby raising the bottom of the conduction bands, and the resultingquantum dot effect is responsible for the color change.
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