Synthesis, crystal structure of Gd(H_2O)(C_2O_4)_2 centre dot NH_4 and of La(C_2O_4)_2 centre dot NH_4. Characterization of the Ln(H_2O)(C_2O_4)_2 centre dot NH_4 with Ln =Eu - Yb

摘要

Single crystals of two lanthanide complexes, presenting similar formula Ln(H_2O)_x(C_2O_4)_2 centre dot NH_4 with Ln = La, x = 0 and La = Gd, x = 1, have been prepared, in closed system at 200 deg C. The gadolinium complex is hi-dimensional. A layer is built by the packing of the basic unit, (Gd(C_2O_4))_4. The gadolinium atoms are related only by bischelating oxalate ligands, the ammonium ion and the water molecule (bound to the gadolinium atom) are localized into the interlayer space. The lanthanum complex is tri-dimensional. The basic building unit remains approximately the same and the packing of these units form a layer. However, within these units, the lanthanum atoms are related by either an oxalate ligand or an edge. Moreover, an oxalate ligand assumes the connection between the layers. The ammonium ion is localized into two sets of intersecting channels. Pure phase of the gadolinium complex has been prepared at 100 deg C and extended to some lanthanide elements, Eu...Yb. As the size of the lanthanide ionic radius is decreasing, it is noticeable that the a unit-cell constant follows an expansion pattern while the others two follow an usual contraction one. The thermal behavior of this family shows that the anhydrous compounds are obtained and that some water molecule is sorbed during the cooling. Thus, the anhydrous compounds present a relatively open-framework with some small micropores.