Inelastic neutron scattering spectrum of Cs2[B12H12]:: Reproduction of its solid-state vibrational spectrum by periodic DFT

The inelastic neutron scattering (INS) spectrum of polycrystalline Cs-2[B12H12] is assigned through 1200 cm(-1) on the basis of aqueous and solid-state Raman/IR measurements and normal mode analyses from solid-state density functional theory. The Cs+ cations are responsible for frequency shifts of the internal cage vibrational modes and I-h cage mode splittings due to the crystal T-h site symmetry. These changes to the [B12H12](2-) molecular modes make isolated-molecule calculations inadequate for use in complete assignments. Solid-state calculations reveal that 30/40 cm(-1) shifts of T-g/H-g molecular modes are responsible for structure in the INS spectrum unobserved by optical methods or in aqueous solutions.