Three new quaternary actinide chalcogenides Ba₂TiUTe₇, Ba₂CrUTe₇, and Ba₂CrThTe₇: Syntheses, crystal structures, transport properties, and theoretical studies

The three new quaternary actinide chalcogenides Ba₂TiUTe₇, Ba₂CrUTe₇, and Ba₂CrThTe₇ have been synthesized. From single-crystal X-ray diffraction studies these isostructural compounds are found to crystallize in a new structure type in space group D2h¹⁶-Pnma of the orthorhombic system. The structure features ∞¹[MAnTe₇^4-] strips (M = Cr or Ti; An = Th or U) that propagate in the b-direction and are separated by Ba cations. An atoms are coordinated to eight Te atoms in a bicapped trigonal-prismatic geometry while M atoms are octahedrally coordinated to six Te atoms. Sharing of the AnTe₈ and MTe₆ polyhedra forms _∞1[MAnTe₇^4-] strips. The presence of the infinite linear Te-Te-Te chains in these compounds makes assignment of oxidation states arbitrary. Resistivity measurements and DFT calculations provide further insight into the properties of these compounds.