U(IV)/LN(III) unexpected mixed in polymetallic oxalato complexes.: Part II.: Substitution of U(IV) for Ln(III) in the new oxalates (N2H5)Ln(C2O4)2 • nH2O (Ln = Nd, Gd)

Two new hydrazinium lanthanide(III) oxalates, (N2H5)[Nd(C2O4)2(H2O)] center dot 4H(2)O (1) and (N2H5)[Gd(C2O4)2(H2O)]center dot 4.5H,0 (2) have been prepared and their crystal structures determined by single-crystal X-ray diffraction. The crystal structures were solved by the direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F-2 for all unique reflections. Crystallographic data: 1, triclinic, space group P1, a = 8.507(3) A, b = 9.762(4), c = 10.249(4) A, a = 62.378(5), beta = 76.681(5), gamma = 73.858(5), Z = 2, R-1 = 0.0335 for 172 parameters with 3430 reflections with I >= 2 sigma(I); 2, triclinic, space group P1, a = 8.52(3) angstrom, b = 9.51(3), c = 10.14(3) angstrom, a = 62.11(4), beta = 76.15(5), gamma = 73.73(5), Z = 2, R-1 = 0.0325 for 172 parameters with 1742 reflections with I >= 2 delta(I). The two isotypic structures are built from a three-dimensional (3D) arrangement of lanthanide and oxalate ions. The lanthanide atom is coordinated by eight oxygen atoms from four tetradentate oxalate ions and one aqua oxygen. Alternating lanthanide and oxalate ions form six-membered rings that delimit tunnels running down three directions and occupied by hydrazinium and water molecules. Starting from these lanthanide(III) compounds two isotypic mixed Ln(III)/U(IV) oxalates, (N2H5)(0.75)[Nd0.75U0.25(C2O4)(2)(H2O)center dot 4.5H(2)O (3) and (N2H5)(0.75)[Gd0.75U0.25(C2O4)(2)(H2O)]center dot 4H(2)O (4), are obtained by partial substitution of Ln(III) by U(IV) in the nine-coordinated site, the charge excess being compensated by removal of monovalent ions from the tunnels. Finally, using. Na+ gel, two mixed Ln(III)/U(IV) sodium oxalates, Na-0.5[Nd0.5U0.5(C2O4)(2)(H2O)]center dot 3H(2)O (5) and Na-0.65[Gd0.65U0.35(C2O4)(2)(H2O)]center dot 4.5H(2)O (6) have been obtained without any change in the 3D framework. (c) 2005 Elsevier Inc. All rights reserved.