title: Temperature- and pressure-induced phase transitions in the metal formate framework of [ND₄][Zn(DCOO)₃] and [NH₄][Zn(HCOO)₃].
abstract: Vibrational properties and the temperature-induced phase transition mechanism have been studied in [NH4][Zn(HCOO)3] and [ND4][Zn(DCOO)3] 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 [ND4][Zn(DCOO)3]. The results indicate the rigidity of the formate ions and strong compressibility of the ZnO6 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.
authors.affiliation: Institute of Low Temperature and Structure Research , Polish Academy of Sciences, Box 1410, 50-950 Wrocław 2, Poland.
authors.forename: Mirosław
authors.initials: M
authors.lastname: Mączka
authors.forename: Paweł
authors.initials: P
authors.lastname: Kadłubański
authors.forename: Paulo Tarso Cavalcante
authors.initials: PT
authors.lastname: Freire
authors.forename: Bogusław
authors.initials: B
authors.lastname: Macalik
authors.forename: Waldeci
authors.initials: W
authors.lastname: Paraguassu
authors.forename: Krysztof
authors.initials: K
authors.lastname: Hermanowicz
authors.forename: Jerzy
authors.initials: J
authors.lastname: Hanuza