Elżbieta Szostak

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 symmetrys 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 223K. 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.

Phase polymorphism of [Ni(DMSO)6](BF4)2 studied by differential scanning calorimetry

The tetrafluoroborate of hexadimethylsulfoxidenickel(II) was synthesized and studied by differential scanning calorimetry. Seven solid phases of [Ni(DMSO)6](BF4)2 were revealed. Specifically, six phase transitions of the first order were detected between the following solid phases: stable KIb → stable KIa at T C6 = 335 K, metastable KIIb → metastable KIIa at T C5 = 368 K, metastable KIII → overcooled phase KI at T C4 = 378 K, metastable KIIa → overcooled phase KI at T C3 = 396 K, stable KIa → stable KI at T C2 = 415 K and stable KI → stable K0 at T C1 = 433 K. [Ni(DMSO)6](BF4)2 begins decomposition at 440 K with loss of one DMSO molecule per formula unit forming [Ni(DMSO)5](BF4)2 (phase L0) which melts next in two steps in the temperature range 550–593 K. From the entropy changes connected both with melting and with phase transitions, it can be concluded that phases KI, overcooled KI and K0 are orientationally dynamically disordered (ODIC) crystals. Stable phases KIb, KIa and metastable phase KIII are ordered solid phases. Metastable phase KIIa and metastable phase KIIb are more or less ordered solid phases.

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

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 TC5(c)=222.9K on cooling and at TC5(h)=225.4K on heating) the CH3 groups perform fast (τR≈10(-12)-10(-13)s) reorientational motions. These motions start to slow down below TC5(c) 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.

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

Three solid–solid phase transitions have been detected for [Sr(OS(CH3)2)4(NO3)2] at T = 229.3 K, T = 220.3 K, and T = 171.6 K (on heating) and at T = 226.6 K, T = 219.1 K, and T = 170.9 K (on cooling). The compound melts at Tm ≈ 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. 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 T 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. 800 K, SrO is formed. Graphical Abstract

Phase transitions and molecular reorientations in [Mn(OS(CH3)2)6](ClO4)2 studied by proton magnetic resonance and Raman spectroscopy

The temperature dependence of full width at half maximum of bands associated with δ d(OClO)F2, δ(CSC), and ρ(CH3) vibrational modes in the FT-RS spectra of [Mn(OS(CH3)2)6](ClO4)2 have shown that the dynamic of reorientational motions of and CH3 groups (from (CH3)2SO) undergoes distinct changes at the phase transitions at T  ≈ 365 K and T  ≈ 322 K. These are the phase transitions from stable crystal to stable rotational phase and from metastable crystal to metastable rotational phase, respectively. Moreover, characteristic changes of the Raman spectra at these phase transitions, connected with both the shift of the band positions and the scattered light intensity of the bands associated with ν s(SO), ν s(MnO), δ(CSC), and δ(OMnO) modes, suggest that these phase transitions are associated with crystal structure changes, too. Analysis of temperature dependence of the second moment (M2) of 1H NMR showed that on first heating (from room temperature) of the compound the reorientations of the CH3 groups were set in motion in the phase transition at T  ≈ 365 K. On subsequent heating (after cooling the compound to 100 K) molecular reorientation starts just above 150 K, and above the temperature of 223 K all molecular groups containing protons perform nearly free rotation with frequencies of a few kHz, including an isotropic reorientation of the whole [Mn(OS(CH3)2)6]2+.

Phase polymorphism of [Cd(DMSO)6](ClO4)2 studied by differential scanning calorimetry

Six solid phases of [Ni(DMSO)6](ClO4)2 have been detected by differential scanning calorimetry (DSC). The five phase transitions were detected between the following solid phases: metastable KIII ↔ undercooled K0 at TC5 = 326 K, stable KIb → stable KIa at TC4 = 350 K, metastable KII ↔ undercooled KI at TC3 = 353 K, stable KIa → stable KI at TC2 = 365 K and stable KI → stable K0 at TC1 = 380 K. At Tm2 = 459 K the title compound partially dissolves in DMSO, which arises from the decomposition of [Ni(DMSO)6](ClO4)2 to [Ni(DMSO)5](ClO4)2, and at Tm1 = 526 K created in this way a substance which completely melts. From the entropy changes at the melting point and at phase transitions it can be concluded that the phases K0 and undercooled K0 are orientationally dynamically disordered crystals. The stable phases KI, KIa, KIb and the metastable phases KII and KIII are more or less ordered solids.

Phase polymorphism of [Zn(OS(CH3)2)6](ClO4)2 studied by vibrational spectroscopy

The FT-IR and FT-RS spectra of [Zn(OS(CH3)2)6](ClO4)2 measured in the spectral range of 4000-90cm(-1) in a function of temperature show distinct differences before and after all three observed phase transitions. The study of temperature dependence of the band position and full width at half maximum allowed us to link each of the observed phase transitions (at: TC1(h)≈355K, TC2(h)≈341K and TC3(h)≈315K) with the changes either of the crystal structure or with the reorientational motions of the dimethylosulphoxide (DMSO) ligands and/or [Zn(OS(CH3)2)6](2+) and/or the ClO4(-) anions and/or with all these changes together.

Phase Polymorphism of [Co(DMSO)6](BF4)2 Studied by Differential Scanning Calorimetry

Five solid phases of [Co(DMSO)6](BF4)2 have been detected by differential scanning calorimetry (DSC). Phase transitions were detected between the following solid phases: stable KIb↔ stable KIa at T̅C4 = (328±2) K, metastable KIII ↔ undercooled phase K0 at T̅C3 = (383±4) K, metastable KII ↔ undercooled K0 at T̅C2 = (399±2) K and stable KIa ↔ stable K0 at T̅C1 = (404±1) K. The title compound melts at Tm = 440 K. From the entropy changes at the melting point and at phase transitions it can be concluded that the phases K0 and undercooled K0 are orientationally dynamically disordered crystals. The stable phases KIa, KIb are ordered solid phases. The metastable phases KII and KIII are probably solid phases with a high degree of orientational dynamical disorder