Vibrational and reorientational dynamics, crystal structure and solid–solid phase transition studies in [Ca(H₂O)₆]Cl₂ supported by theoretical (DFT) calculations

Abstract

[Ca(H2O)6]Cl2 between 93 and 300 K possesses two solid phases. One phase transition (PT) of the first‐order type at TCh = 218.0 K (on heating) and TCc = 208.0 K (on cooling) was determined by differential scanning calorimetry. Thermal hysteresis of this PT (10 K), as well as the heat flow anomaly sharpness, suggests that the detected PT is a first‐order one. The entropy change value [ΔS ≈ 8.5 J mol−1 K−1 ≈ Rln(2.8)] associated with the observed PT suggests a moderate degree of molecular dynamical disorder of the high‐temperature phase. The temperature dependencies of the full width at half maximum values of the infrared band are due to ρ(H2O)A2 mode (at 205 cm−1), and two Raman bands are arising from τ(H2O)E and τ(H2O)A1 modes (at ca. 410 and 682 cm−1, respectively), suggesting that the observed PT is associated with a sudden change of speed of the H2O reorientational motions. The estimated mean value of activation energy for the reorientation of the H2O ligands in the high‐temperature phase is ca. 11.4 kJ mol−1 from Raman spectroscopy and 11.9 kJ mol−1 from infrared spectroscopy. X‐ray single‐crystal diffraction measurement and spectroscopic studies (infrared, Raman and inelastic neutron scattering) also confirm that [Ca(H2O)6]Cl2 includes two sets of differently bonded H2O molecules. Ab initio calculations of the complete unit cell of one molecule of calcium chloride with a different number of water molecules (2, 4 and 6) have also been carried out. A comparison of Fourier Transform Infrared (FT‐IR), Fourier Transform Raman Scattering (FT‐RS) and inelastic neutron scattering spectroscopies results with periodic density functional theory calculations was used to provide a complete assignment of the vibrational spectra of [Ca(H2O)6]Cl2. Copyright © 2016 John Wiley & Sons, Ltd.

Vibrational Properties of Bulk Boric Acid 2A and 3T Polymorphs and Their Two-Dimensional Layers: Measurements and Density Functional Theory Calculations

“…For the isolated boric acid molecule, the normal modes below 1000 cm –1 are shifted downward in comparison to those of the crystal and have fewer features in common with the latter (only four maxima can be discerned, while the theoretical curves exhibit five). Overall, the data we present are in agreement with other experimental reports − (see Table ) and surpass the quality of estimates which were performed using a more accurate exchange-correlation functional but without van der Waals corrections. , …”

Crystal structure, phase transitions and vibrations of H2O molecules in [Ca(H2O)2](ReO4)2

“…The Ca atoms in this structure are coordinated by nine O atoms. The coordination geometry of the calcium ion can be best approximated as monocapped square antiprism CaO 6 (H 2 O) 3 . The same Crystal system Monoclinic Space group I 2/a Unit cell dimensions a = 18.1302(7) Å a = 90.000 (5) (4)O (5)O (9), respectively, while O(3) can be considered as the capping atom (see Fig.…”

“…complex cations. Similar compounds with the same ligand [1][2][3] and anion [4,5] exhibit also an interesting polymorphism.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…Hetmanczyk and co‐workers reported the vibrational and reorientational dynamics, crystal structure, and solid‐solid phase transition studies in Ca(H 2 O) 6 ]Cl 2 that were supported by theoretical (DFT) calculations. A comparison of FT‐IR, FT‐Raman, and inelastic neutron scattering results with periodic DFT calculations provided a complete assignment of the vibrational spectra of [Ca(H 2 O) 6 ]Cl 2 . Kumari et al presented a study aimed at understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated metal organic frameworks (MOF) that are interesting functional materials exhibiting exceptional framework properties.…”

“…A comparison of FT-IR, FT-Raman, and inelastic neutron scattering results with periodic DFT calculations provided a complete assignment of the vibrational spectra of [Ca(H 2 O) 6 ] Cl 2 . [147] Kumari et al presented a study aimed at understanding guest and pressure-induced porosity through structural transition in flexible interpenetrated metal organic frameworks (MOF) that are interesting functional materials exhibiting exceptional framework properties. The authors investigated structural transformations in MOF-508 under variable conditions of temperature, pressure, and gas loading using Raman spectroscopy and supported these results with IR studies and DFT calculations.…”