UTa2O(S2)3Cl6: A ribbon structure containing a heterobimetallic 5d–5f M3 cluster

A new solid-state compound containing a heterobimetallic cluster of U and Ta, UTa2O(S2)3Cl6, has been synthesized and its structure has been characterized by single-crystal X-ray diffraction methods. UTa2O(S2)3Cl6 was synthesized from UCl4 and Ta1.2S2 at 883 K. The O is believed to have originated in the Ta1.2S2 reactant. The compound crystallizes in the space group P1¯ of the triclinic system. The structure comprises a UTa2 unit bridged by μ2-S2 and μ3-O groups. Each Ta atom bonds to two μ2-S2, the μ3-O, and two terminal Cl atoms. Each U atom bonds to two μ2-S2, the μ3-O, and four Cl atoms. The Cl atoms bridge in pairs to neighboring U atoms to form a ribbon structure. The bond distances are normal and are consistent with formal oxidation states of +IV/+V/–II/–I/–I for U/Ta/O/S/Cl, respectively. The optical absorbance spectrum displays characteristic transition peaks near the absorption edge. Density functional theory was used to assign these peaks to transitions between S1– valence-band states and empty U 5f–6d hybrid bands. Density-of-states analysis shows overlap between Ta 5d and U bands, consistent with metal–metal interactions.