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 U4+ and divalent transition metal cations, Na2U2M­(C2O4)6(H2O)4 (M = Mn2+, Fe2+, Co2+, and Zn2+), were synthesized via a hydrothermal route and structurally characterized by single crystal X-ray diffraction. All of the materials are triclinic, with space group P1̅. The three-dimensional structure of these isostructural uranates consists of oxalate bridged UO10 and MO6 polyhedra. The U4+ cation is surrounded by five oxalate ligands, while the M2+ 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 μB for U4+ cation in the Zn member, while the total effective moment of the Mn2+, Fe2+, and Co2+ members are 6.01, 5.46, and 5.06 μB, respectively. For all materials, negative Weiss constants were observed revealing that the materials exhibited local antiferromagnetic interactions. The U4+ cation exhibits a singlet ground state at low temperature. The materials were further characterized by infrared, UV–vis reflectance spectroscopy, and thermal analysis.