Crystal Structure of Cerium Magnesium Nitrate Hydrate

According to single-crystal x-ray diffraction data, crystals of Ce2Mg3(NO3)12·24H2O are rhombohedral, space group R3̄. The hexagonal cell with a = 11.004±0.006, c = 34.592±0.012 Å contains three formula units. Atomic parameters were refined by least squares, and interatomic distances were corrected for thermal motion. The average N–O bond distance in nitrate is 1.26 Å. The Ce atoms, on the threefold axis at z = ±0.2497, are each surrounded by 12 oxygen atoms at an average distance of 2.64 Å. These oxygen atoms, belonging to six nitrate ions, are at the corners of a somewhat irregular icosahedron. The Mg atoms are of two kinds, located, respectively, at the origin and on the threefold axis at z = ±0.4279. Each Mg atom is surrounded by six water molecules with the oxygen atoms at the corners of an octahedron with an average Mg–O distance of 2.07 Å. One-fourth of the water molecules are not coordinated to cations. Evidence for the hydrogen atom positions from the diffraction data indicates that six of the eight independent hydrogen atoms are involved in normal hydrogen bonds.