Temperature- and Pressure-Induced Phase Transitions in the Metal Formate Framework of [ND<sub>4</sub>][Zn(DCOO)<sub>3</sub>] and [NH<sub>4</sub>][Zn(HCOO)<sub>3</sub>]
journal contribution
posted on 2015-12-17, 04:22 authored by Mirosław Mączka, Paweł Kadłubański, Paulo Tarso Cavalcante Freire, Bogusław Macalik, Waldeci Paraguassu, Krysztof Hermanowicz, Jerzy HanuzaVibrational
properties and the temperature-induced phase transition mechanism
have been studied in [NH<sub>4</sub>][Zn(HCOO)<sub>3</sub>] and [ND<sub>4</sub>][Zn(DCOO)<sub>3</sub>] metal organic frameworks by variable-temperature
dielectric, IR, and Raman measurements. DFT calculations allowed proposing
the detailed assignment of vibrational modes to respective motions
of atoms in the unit cell. Temperature-dependent studies reveal a
very weak isotopic effect on the phase transition temperature and
confirm that ordering of ammonium cations plays a major role in the
mechanism of the phase transition. We also present high-pressure Raman
scattering studies on [ND<sub>4</sub>][Zn(DCOO)<sub>3</sub>]. The
results indicate the rigidity of the formate ions and strong compressibility
of the ZnO<sub>6</sub> octahedra. They also reveal the onset of a
pressure-induced phase transition at about 1.1 GPa. This transition
has strong first-order character, and it is associated with a large
distortion of the metal formate framework. Our data indicate the presence
of at least two nonequivalent formate ions in the high-pressure structure
with very different C–D bonds. The decompression experiment
shows that the transition is reversible.
