Low-temperature phase transition in [Mn(OS(CH3)2)6](ClO4)2 studied by single crystal X-ray diffraction, infrared absorption and Raman scattering spectroscopies

Single crystal X-ray diffraction studies of [Mn(OS(CH3)2)6](ClO4)2 have shown that the low temperature phase transition, detected by differential scanning calorimetry (DSC) at about 223 K, is associated with the crystal symmetry's reduction from an orthorhombic crystallographic system (Fdd2, No. 43) to a monoclinic one (Cc, No. 9). The analysis of the full width at half maximum of the bands connected with: δd(OClO)F2 and ρ(CH3) vibrational modes in the FT-IR and FT-RS spectra, respectively, registered in the function of temperature, proved that the reorientational motions of ClO4− anions and CH3 groups from (CH3)2SO ligands, began to slow down at temperatures below the phase transition at about 223 K. Mean values of activation energy for ClO4− reorientation in the high temperature phase I and low temperature phase II are: Ea(I) ≈ 14 kJ mol−1 and Ea(II) ≈ 10 kJ mol−1, respectively. Analogous values for CH3 reorientation are: Ea(I) ≈ 23 kJ mol−1 and Ea(II) ≈ 1 kJ mol−1, respectively.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Study of relationships between the phase transition and the crystal structure change. ► X-ray diffraction, infrared absorption and Raman light scattering measurements. ► Changes of the crystal structure and reorientational molecular dynamic. ► Determination of activation energy values for reorientational motions of ClO4 and CH3 groups.