Syntheses, crystal structures, and properties of Ln(4)Au(2)O(9), (Ln = Nd,Sm, Eu)

The compounds Ln(4)Au(2)O(9) (Ln=Nd, Sm, Eu) have been prepared from amorph ous Au2O3. 2-3H(2)O and Ln(2)O(3) (Ln = Nd. Sm, Eu) via solid state reactio n under elevated-oxygen pressure adding KOH as mineralising agent. They are isostructural with La4Au2O9 (Nd4Au2O9: a= 11.9813(3), b=6.1474(1), c=11.96 41(4); 453 powder intensi ties, R-p=3.75%; Sm4Au2O9: a=11.8689(4), b=6.0360 (1), c=11.8469(4) Angstrom: 812 unique reflections, R-1 = 2.75%; Eu4Au2O9: a=11.8241(3), b=5.9922(1) Angstrom,c=11.8013(3) Angstrom; 1315 unique refle ctions, R-1 = 7.83%). The crystal structure of Nd4Au2O9 was refined from po wder diffraction data. The structures of Sm4Au2O9 and Eu4Au2O9 were solved and refined from single crystal data. The isolated square planar AuO4 units are stacked as columns and are linked to each other by LnO(7)-polyhedra. O ne of the oxygen atoms is exclusively connected to the trivalent lanthanide s in tetrahedral geometry. Ln(4)Au(2)O(9), Bi2CuO4, Bi2AuO5 and Bi4Au2O9 ar e closely related, structurally. The lanthanoid aurates decompose between 7 00 and 800 degrees C into Ln(2)O(3), Au and O-2 The effective magnetic mome nts 3.64 mu(B) (Nd4Au2O9), 1.7 mu B (Sm4Au2O9) and 3.3 mu B (Eu4Au2O9,) con firm that the lanthanides are trivalent. The UV/VIS absorption spectra can be interpreted at assuming free ions.