New ternary uranium copper chalcogenides Cu2U3S7 and Cu2U3Se7: Crystal structure and magnetic properties

The new compounds Cu2U3S7 and Cu2U3Se7 have been synthesized by direct reaction between UX(2) (X = S,Se), Cu, and chalcogens at 600 degrees C, Single crystals were obtained using the chemical vapor transport method, The compounds crystallize in the hexagonal system with a = 9.7308(8), c = 5.7045(6) Angstrom for Cu2U3S7 and a = 10.138(1), c = 5.9525(7) A for Cu2U3Se7. The crystal structures of the two compounds were solved in the space group P6(3) and refined to the final values of the reliability factors R = 0.031, R(omega) = 0.038 for Cu2U3S7 and R = 0.036, R(omega) = 0.044 for Cu2U3Se7. They are isotypic with La3CuSiS7. Magnetic measurements showed that Cu2U3S7 presents a paramagnetic behaviour down to 5 K while Cu2U3Se7 exhibits an antiferromagnetic transition at T-N = 13 K. (C) 1996 Academic Press, Inc.