A comprehensive study on crystal structure, thermal behavior, and molecular dynamics of [Sr(DMSO)₄(NO₃)₂]

<div><p>Three solid–solid phase transitions have been detected for [Sr(OS(CH₃)₂)₄(NO₃)₂] at <i>T</i> = 229.3 K, <i>T</i> = 220.3 K, and <i>T</i> = 171.6 K (on heating) and at <i>T</i> = 226.6 K, <i>T</i> = 219.1 K, and <i>T</i> = 170.9 K (on cooling). The compound melts at <i>T</i>_m ≈ 347 K. Thermal behavior of the deuterated analog is essentially the same, but the phase transitions’ temperatures are shifted slightly towards higher temperature, by ca<i>.</i> 5, 5, and 15 K, respectively. Crystal structure in the lowest temperature of phase III at 93 K consists of completely ordered (CH₃)₂SO molecules and bidentate nitrate groups, which are coordinated to strontium cation. Infrared (IR) spectra reveal that the phase transition at <i>T</i> is associated with the slowing down of the reorientational motions of (CH₃)₂SO and NO₃^– groups and also with the lowering of crystal lattice symmetry of the compound. The extended solid-state vibrational analysis has been performed for both deuterated and protonated species by solid-state density functional theory computations and compared with IR and RS experimental spectra. Thermal decomposition occurs in two stages: in the first stage, in four steps, four (CH₃)₂SO molecules are liberated and Sr(NO₃)₂ is formed, and in the second stage, above ca<i>.</i> 800 K, SrO is formed.</p>