Raman and infrared spectroscopic studies on Li₄RuH₆combined with first-principles calculations

We have studied the vibrational properties of Li₄RuH₆, consisting of the lightest Li⁺metal cation, and the octahedral [RuH₆]^4-complex anion by Raman and Fourier Transform Infrared (FTIR) spectroscopies and first-principles calculations. The Li⁺forms a cubic framework with the [RuH₆]^4-inside as the local atomic arrangement of Li₄RuH₆, which is similar to that of a related M′₂RuH₆with a divalent metal cation MB (MB = Mg, Ca, Sr, Ba, and Yb). Comparing the vibrational studies on Li₄RuH₆with M′₂RuH₆, the peak frequencies for the antisymmetric RuH stretching mode (Vanti-str) showed a reasonable relationship with the Ru-H bond distances (d_Ru-H) in [RuH₆]^4-, with higher peak frequencies for shorter bond distances according to the linear relation Vanti-str = 10052 - 4990 × (d_Ru-H).