Comparison of vibrational dynamics, thermal behaviour, and phase transition in [Ni(NH3)4](ReO4)2[Ni(NH_3)_4](ReO_4)_2 and [Ni(NH3)6](ReO4)2[Ni(NH_3)_6](ReO_4)_2

The differences between thermal and vibrational properties of $[Ni(NH_3)_4](ReO_4)_2$ and $[Ni(NH_3)_6](ReO_4)_2$ are reported. The differential scanning calorimetry revealed that tetraamminenickel(II) perrhenate exhibits, in the temperature range of 300–140 K, one phase transition at ca. T c h = 188 K (on heating) and T c c = 185 K (on cooling). In the case of hexaamminenickel(II) perrhenate, no phase transition was observed in the same temperature region. Thermogravimetric measurements showed that the decomposition proceeds in the two main stages. In the first stage, a complete deammination takes place and next $Re_2O_7$ is released. TG measurements showed that $NH_3$ molecules are not equivalently bonded to central atom. The final and intermediate products of decomposition were analysed by means of infrared spectroscopy. The final product of thermal decomposition of both compounds is nickel(II) oxide. The analysis of far infrared spectra revealed that anions in $[Ni(NH_3)_6](ReO_4)_2$ have disturbed tetrahedral symmetry, whereas in $[Ni(NH_3)_4](ReO_4)_2$ they seem to form polymeric chains. The variation of the activation energies of the deammination and decomposition steps of $[Ni(NH_3)_6](ReO_4)_2$ was calculated through the model-free isoconversional Kissinger–Akahira–Sunose method and model-free Kissinger method. Infrared spectra were calculated by the DFT method and quite a good agreement with the experimental data was obtained

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

Molecular foundations of chilling-tolerance of modern maize

Gene Ontology categories of GO class “Molecular Function” significantly over-represented among transcripts down-regulated by cold treatment in S50676 inbred line. (PDF 233 kb