Deviation between the\nStructural Chemistry of Barium\nand Radium Halides: Synthesis and Characterization of RaX<sub>2</sub>·H<sub>2</sub>O and RaX<sub>2</sub>·2H<sub>2</sub>O (X<sup><b>–&lt

To develop the structural chemistry of radium, the halide\ncompounds\nRaX<sub>2</sub>·H<sub>2</sub>O and RaX<sub>2</sub>·2H<sub>2</sub>O (X<sup>–</sup> = Cl<sup>–</sup> and Br<sup>–</sup>) have been synthesized and characterized and serve\nas benchmarks for comparisons with more complex compounds in the future.\nIn contrast with historic reports on the structural chemistry of radium,\nthe Ra<sup>2+</sup> chlorides differ from their Ba<sup>2+</sup> analogues.\nFor MCl<sub>2</sub>·H<sub>2</sub>O (M<sup>2+</sup> = Ba<sup>2+</sup>, Ra<sup>2+</sup>), the variance between the metal coordination environments\nmanifests as a small, local distortion that becomes more apparent\nin the extended structure. However, differences between RaCl<sub>2</sub>·2H<sub>2</sub>O and BaCl<sub>2</sub>·2H<sub>2</sub>O are\nmore pronounced with a 10-coordinate Ra<sup>2+</sup> cation being\nobserved instead of a nine-coordinate Ba<sup>2+</sup> in BaCl<sub>2</sub>·2H<sub>2</sub>O. RaBr<sub>2</sub>·<i>n</i>H<sub>2</sub>O (<i>n</i> = 1 or 2) are isomorphous with\nthe Ba<sup>2+</sup> analogues. Raman spectroscopy was used as an additional\nprobe of these compounds and reveals substantial shifts and different\nvibrational modes between RaX<sub>2</sub>·H<sub>2</sub>O and\nRaX<sub>2</sub>·2H<sub>2</sub>O compared to BaX<sub>2</sub>·2H<sub>2</sub>O.