The First Examples of Alkali Metal/Cu/Ce/Chalcogenides: The Layered Heterometallic Compounds KCuCe2S6 and K2Cu2CeS4
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From the reaction of the metallic elements in molten alkali metal/polychalcogenide fluxes, we have synthesized KCuCe{sub 2}S{sub 6} (I) and K{sub 2}Cu{sub 2}CeS{sub 4} (II). Isolated from a 2/0.5/1/8 mixture of K{sub 2}S/Cu/Ce/S heated at 270{degree}C for 6 d, I crystallizes in the space group C2/c (no. 15) with a = 6.859(2) A, b = 21.154(2) A, c = 6.8599(8) A, {beta} = 105.41(2){degree}, and Z = 4. The structure of I features (CuCe{sub 2}S{sub 6}){sub n}{sup n-} anionic layers composed of [CeS{sub 8}] bicapped trigonal prisms connected in the ZrSe{sub 3} fashion with Cu{sup +} residing in tetrahedral sites within the layers and K{sup +} cations in the interlayer gallery. Diffuse reflectance measurements have shown an approximated band gap of 1.8 eV for I, and magnetic studies exhibit Curie-Weiss paramagnetic behavior at temperatures above 160 K with {mu}{sub eff} = 3.08 {mu}{sub 8}/formula. Isolated from a 4.2/0.5/0.25/8 mixture of the above reagents heated at 260{degree}C for 5d, II crystallizes in the C2/m space group (no. 12) with a = 14.320(3) A, b = 3.961(1) A, c = 7.496(2) A, {beta} = 109.77(2){degree}, and Z = 2. Compound II is also a layered structure in which Ce atoms, octahedrally coordinatedmore » by S, and Cu, tetrahedrally coordinated by S, form anionic layers related to Mg{sub 2}SiO{sub 4} (olivine) with K{sup +} in the interlayer gallery. 38 refs., 10 figs., 3 tabs.« less