Syntheses and characterization of nine quaternary uranium chalcogenides among the compounds A ₂M ₃UQ ₆ (A = K, Rb, Cs; M = Pd, Pt; Q = S, Se)

Nine compounds from the series A ₂M ₃UQ ₆ (A = K or Rb or Cs; M = Pd or Pt; Q = S or Se) were synthesized by reacting U, M, and Q in ACl or A ₂Q _x fluxes. These compounds crystallize with eight formula units in the NaBa ₂Cu ₃O ₆ structure type, in space group Fmmm of the orthorhombic system. The structure contains hexagons formed from six edge-sharing square-planar coordinated M atoms, which in turn edge-share with trigonal-prismatically coordinated U atoms, forming layers along (010). These layers are separated by A atoms. Electrical resistivity measurements along the [100] direction of Rb ₂Pd ₃US ₆ show typical semiconductor behavior. Magnetic susceptibility measurements on Rb ₂Pd ₃US ₆ display marked magnetic anisotropy and unusually low magnetic moments owing to crystalline electric field effects.