Low-temperature and pressure-induced conformational change in Tutton salt K2Ni(H2O)6(SO4)2: Structural, vibrational
Raí F Jucá1, Tiago S Pacheco2, João G de Oliveira Neto3
1Department of Physics, Federal University of Sergipe 49100-000 Sergipe, Brazil.
Abstract:
The crystal structure of the Tutton salt K2Ni(H2O)6(SO4)2 was synthesized via the slow evaporation method in an aqueous solution and refined as monoclinic symmetry, belonging to the P21/a(C2h5)-space group, with two formula per unit cell (Z = 2). Intermolecular interactions within the crystal were analyzed using Hirshfeld surfaces. Periodic-DFT calculations were conducted to obtain the electronic properties,explored throughthe band structure and projected density of states (PDOS), as well as Raman and infrared mode assignments. Spectral analysis spanning from 80 to 3600 cm-1 indicated that no phase transitions occurred during cooling (from 300 K to 9 K), confirming the structural stability of the crystal. However, the nonlinear temperature dependence of Raman modes suggested conformational changes affecting bond lengths and angles. A decrease in Raman intensity at 60 K, particularly in spectral regions associated with water and sulfate vibrations, indicated significant conformational modifications. Similarly, pressure-dependent Raman spectra (ranging from 0.0 GPa to 7.05 GPa) showed changes in wavenumber and bandwidth, reinforcing the hypothesis that water bond vibrations drive conformational changes. Finally, the magnetic characterization revealed paramagnetic behavior at room temperature and antiferromagnetic interactions at low temperatures.
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