Synthesis, crystal structure, resistivity, and electronic structure of the U(V) quaternary poly-selenide Ba₈PdU₂Se₁₂(Se₂)₂

A new quaternary uranium(V) selenide, Ba₈PdU₂Se₁₂(Se₂)₂, has been synthesized by reaction of elements at 1173 K. A single-crystal X-ray diffraction study shows that the compound crystallizes in a new structure type with two formula units in space group D_2h¹²-Pnnm of the orthorhombic crystal system with cell constants of a=9.490(1), b=12.240(2),and c=13.780(3) Angstroms. Its crystal structure consists of [PdU₂Se₁₂^12-] units where U atoms are coordinated to six Se atoms in octahedral geometry and Pd atoms are coordinated to four Se atoms in square-planar geometry.These [PdU₂Se₁₂^12-] units are separated by Ba to result in a salt-like crystal structure. This compound also contains Se₂^2- dimers that are part of Ba coordination polyhedra. The formula charge balances as (Ba²⁺)₈(Pd²⁺)(U⁵⁺)₂(Se^2-)₁₂(Se₂^2-)₂. Theoretical calculations predict antiferromagnetic semiconducting behavior for this compound with a band gap of 1.6 eV. Temperature-dependent four-probe resistivity measurements on single crystal confirm the semiconducting nature with an activation energy of 0.18(1)eV. (authors)