Cs₈[Fe₄S₁₀] and Cs₇[Fe₄S₈], Two New Sulfido Ferrates with Different Tetrameric anions

The two new cesium sulfido ferrates Cs₈[Fe₄S₁₀] and Cs₇[Fe₄S₈] were synthesized at a maximum temperature of 1070 K in corundum crucibles from stoichiometric samples containing elemental Fe and S together with cesium disulfide, Cs₂S₂. Their crystal structures have been determined by means of single-crystal X-ray diffraction. Cs₈[Fe^III₄S₁₀] crystallizes in the triclinic Cs₆[Ga₄Se₁₀]-type structure and is thus isotypic to the corresponding rubidium salt. The structure exhibits tetramers [Fe₄S₁₀]^8– of edge-sharing tetrahedra, which represent segments of the well-known chain compounds A­[FeS₂]. The monoclinic mixed-valent iron­(II/III) sulfido ferrate Cs₇[Fe₄S₈], which is isotypic to the cesium tellurido ferrate, likewise contains oligomeric tetramers of four edge-sharing [FeS₄] tetrahedra, in this case resulting in only slightly distorted tetrahedral [Fe₄S₈]^7– anions with a Fe₄S₄ cubane core resembling the prominent [Fe₄(μ₃-S₄)]⁺ cluster, e.g., in the active site of ferredoxins. These sulfido ferrate anions are surrounded by 26 Cs cations, which are located at the 8 corners, 6 faces, and 12 edges of a cube. A dense stacking of these cubes, which ultimately results in the overall seven cesium countercations per cluster anion, describes the overall crystal structure completely. According to this arrangement of cluster-centered cubes, a relationship of the packing of Cs cations and cluster anions with the simple cubic packing (α-Po-type structure) can be established by applying the crystallographic group–subgroup formalism. FP-LAPW band-structure calculations applying antiferromagnetic spin ordering of the high-spin Fe ions in the two tetramers predict a small band gap of 1 eV associated with a L → M-CT for Cs₈[Fe^III₄S₁₀] and a tiny energy gap of 0.1 eV resulting from a d–d transition for the mixed-valent cluster compound Cs₇[Fe^II/III₄S₈]

Biomimetic Asymmetric Synthesis of (<i>R</i>)-GTRI-02 and (3<i>S</i>,4<i>R</i>)-3,4-Dihydroxy-3,4-dihydronaphthalen-1(2<i>H</i>)-ones

The NADPH-dependent tetrahydroxynaphthalene reductase (T₄HNR) from <i>Magnaporthe grisea</i> was used for the biomimetic synthesis of (<i>R</i>)-GTRI-02 by stereoselective reduction of 1-(3,6,8-trihydroxy-1-methylnaphthalen-2-yl)ethanone. This also led to the isolation of a (3<i>S</i>,4<i>R</i>)-<i>cis</i>-ketodiol formed by T₄HNR-catalyzed reduction of the corresponding hydroxynaphthoquinone. Flaviolin and lawsone also reduced to corresponding <i>cis</i>-ketodiols in good yields

Biomimetic Asymmetric Synthesis of (<i>R</i>)-GTRI-02 and (3<i>S</i>,4<i>R</i>)-3,4-Dihydroxy-3,4-dihydronaphthalen-1(2<i>H</i>)-ones

The NADPH-dependent tetrahydroxynaphthalene reductase (T₄HNR) from <i>Magnaporthe grisea</i> was used for the biomimetic synthesis of (<i>R</i>)-GTRI-02 by stereoselective reduction of 1-(3,6,8-trihydroxy-1-methylnaphthalen-2-yl)ethanone. This also led to the isolation of a (3<i>S</i>,4<i>R</i>)-<i>cis</i>-ketodiol formed by T₄HNR-catalyzed reduction of the corresponding hydroxynaphthoquinone. Flaviolin and lawsone also reduced to corresponding <i>cis</i>-ketodiols in good yields