The [U<sub>2</sub>(μ‑S<sub>2</sub>)<sub>2</sub>Cl<sub>8</sub>]<sup>4–</sup> Anion: Synthesis and Characterization of the Uranium Double Salt Cs<sub>5</sub>[U<sub>2</sub>(μ‑S<sub>2</sub>)<sub>2</sub>Cl<sub>8</sub>]I
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Red plates of Cs5[U2(μ-S2)2Cl8]I were obtained in good yield from the reaction at 1173 K of U, GeI2 or SnI4, and S, with CsCl flux. The compound crystallizes in space group D2h25-Immm of the orthorhombic system in the Cs5[Nb2(μ-S2)2Cl8]Cl structure type. The centrosymmetric [U2(μ-S2)2Cl8]4– anion in the structure has mmm symmetry with the two U4+ atoms separated by 3.747(1) Å. Each U atom is coordinated to four Cl atoms and four S atoms from two S22– groups in a square-antiprismatic arrangement. The polarized absorbance spectra of Cs5[U2(μ-S2)2Cl8]I display prominent optical anisotropy. Magnetic measurements are consistent with the modified Curie–Weiss law at high temperatures. The low-temperature behavior may arise from antiferromagnetic coupling of the U4+ ions within the anion.
