Vibrational Frequencies and Force Constants for Tetrahedral MgX4−2 (X=Cl, Br, and I) in MgX2–KX Melts

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Raman spectra are reported for the species present in MgX2–KX melts (X=Cl, Br, and I) with X−1/Mg+2 mole ratios near 4.0. The observation of one polarized band and three depolarized bands for each halide melt is consistent with the existence of the tetrahedral complexes MgCl4−2, MgBr4−2, and MgI4−2. All the observed frequencies are calculated within 1 cm−1 using a Urey—Bradley force field which consists of an Mg–X stretching constant, an X–Mg–X bending constant, and an X ··· X repulsion constant.