Inelastic and elastic neutron scattering studies of the vibrational and reorientational dynamics, crystal structure and solid–solid phase transition in [Mn(OS(CH3)2)6](ClO4)2 supported by theoretical (DFT) calculations

• Structure and molecular reorientations in [Mn(OS(CH3)2)6](ClO4)2 studied by neutron scattering methods.
• FT-IR, RS and IINS spectra calculated by DFT method compared with experimental results.
• The NPD patterns of [Mn(OS(CH3)2)6](ClO4)2 confirm the structural character of low temperature phase transition.
• The QENS data registered at 200 and 5 K do not show any broadening.

The vibrational and reorientational dynamics of CH3 groups from (CH3)2SO ligands in the high- and low-temperature phases of [Mn(OS(CH3)2)6](ClO4)2 were investigated by quasielastic and inelastic incoherent neutron scattering (QENS and IINS) methods. The results show that above the phase transition temperature (detected earlier by differential scanning calorimetry (DSC) at TC5c = 222.9 K on cooling and at TC5h = 225.4 K on heating) the CH3 groups perform fast (τR ≈ 10−12–10−13 s) reorientational motions. These motions start to slow down below TC5c Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS and IINS, indicated that this phase transition is associated with a change of the crystal structure, too. Theoretical infrared absorption, Raman and inelastic incoherent neutron scattering spectra were calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on C, H, S, O atoms) for the isolated equilibrium model (isolated [Mn(DMSO)6]2+ cation and ClO4− anion). Calculated spectra show a good agreement with the experimental spectra (FT-IR, RS and IINS). The comparison of the results obtained by these complementary methods was made.

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