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 Cs2B12H12] 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 Tg/Hg molecular modes are responsible for structure in the INS spectrum unobserved by optical methods or in aqueous solutions.