Thermal properties of polycrystalline [Mn(NH3)6](ClO4)2[Mn(NH_{3})_{6}](ClO_{4})_{2} : crystal structure and phase transitions

The X-ray powder diffraction (XRPD) pattern of [Mn(NH 3 ) 6 ](ClO 4 ) 2 at room temperature can be indexed in the regular (cubic) system (Fm 3m space group) with lattice cell parameter a = 11.5729 A ̊ and with four mole- cules per unit cell. The XRPD pattern at 100 K is evidently different, and it indicates lowering of the crystal structure. One phase transition at T h C1 = 143.5 K (on heating) and at T c C1 = 137.6 K (on cooling) was detected by DSC for [Mn(NH 3 ) 6 ](ClO 4 ) 2 in the range of 120–300 K. The fol- lowing thermodynamic parameters for phase I $ phase II transition were obtained: D H = 3.1 ± 0.2 kJ mol - 1 and D S = 21.6 ± 0.3 J mol - 1 K - 1 . The large value of entropy changes ( D S ) indicates considerable configurational disor- der in the high temperature phase. The presence of 5.9 K hysteresis of the phase transition temperature at T C and sharpness of the heat flow anomaly attest that the detected phase transition is of the first-order type. Appearing of the two new bands (splitting of d s (HNH) F 1u mode) in FT-MIR spectra at the vicinity of 1200 cm - 1 suggests that the phase transition undergoes a change of the crystal structure

Thermal properties of [Cr(NH3)6](BF4)3[Cr(NH_3)_6](BF_4)_3 studied by adiabatic and relaxation calorimetry

Four (solid–solid) phase transitions were detected in the temperature range of (9 to 300) K in polycrystalline [Cr(NH3)6](BF4)3 at TC1 = 240.7 K, TC2 = 108.0 K, TC3 = 91.9 K, and TC4 = 61.3 K by adiabatic calorimetry. The measurements by relaxation calorimetry were followed on lowering temperature from 20 K down to 0.35 K under six different external magnetic field values (9, 7, 5, 3, 1 and 0) T. For non-zero values of applied magnetic field well-defined Schottky anomaly appears. Magnetic heat capacity was calculated assuming the zero-field splitting for the decoupled Cr(III) ions. There is no discrepancy between the observed and calculated values. Isothermal magnetization curve recorded up to 5 T was measured at temperature of 1.8 K

Phase polymorphism, molecular motions and structural changes in [Cr(NH3)6](ClO4)3[Cr(NH_3)_6](ClO_4)_3

A phase transition in [Cr(NH3)6](ClO4)3 at Th c = 293.5 K (on heating) and Tc c = 293.0 K (on cooling) was determined by differential scanning calorimetry. The temperature dependences of the full width at half maximum of the bands connected with ρr(NH3)F1u and δd(ClO)E modes suggest that the discovered phase transition is not connected with drastic changes in the speed of reorientational motions of the NH3 ligands nor the ClO4 − anions. Temperature dependence of the FT-FIR spectra and the diffraction patterns show that the discovered phase transition is caused by a change in the crystal structure.</jats:p

IINS, FT-IR and DFT study of the internal dynamics of [4-apyH][SbCl4SbCl_4]

A combination of infrared and inelastic incoherent neutron scattering spectroscopies with the density functional theory and semi-empirical calculations was applied to propose an assignment of the vibrational spectra of 4-aminopyridine chloroantimonate(IV)