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 Ta_1.2S₂ at 883 K. The O is believed to have originated in the Ta_1.2S₂ 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 S^1- 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.