Crystal growth, structural characterization, and magnetic properties of new uranium(IV) containing mixed metal oxalates: Na2U2M(C2O4)6(H2O)4 (M = Mn2+, Fe2+, Co2+, and Zn2+).

A series of new mixed-metal oxalates containing U(4+) and divalent transition metal cations, Na(2)U(2)M(C(2)O(4))(6)(H(2)O)(4) (M = Mn(2+), Fe(2+), Co(2+), and Zn(2+)), were synthesized via a hydrothermal route and structurally characterized by single crystal X-ray diffraction. All of the materials are triclinic, with space group P1. The three-dimensional structure of these isostructural uranates consists of oxalate bridged UO(10) and MO(6) polyhedra. The U(4+) cation is surrounded by five oxalate ligands, while the M(2+) cations are bonded to two oxalate ligands and four water molecules. The magnetic susceptibility data of these mixed metal oxalates were measured as a function of temperature and result in a value of the effective magnetic moment of 3.50 μ(B) for U(4+) cation in the Zn member, while the total effective moment of the Mn(2+), Fe(2+), and Co(2+) members are 6.01, 5.46, and 5.06 μ(B), respectively. For all materials, negative Weiss constants were observed revealing that the materials exhibited local antiferromagnetic interactions. The U(4+) cation exhibits a singlet ground state at low temperature. The materials were further characterized by infrared, UV-vis reflectance spectroscopy, and thermal analysis.