Unusual isosymmetric order–disorder phase transition in a new perovskite-type dimethylhydrazinium manganese formate exhibiting weak ferromagnetism and photoluminescence properties

Abstract

We report the synthesis, thermal, structural, dielectric, magnetic and optical properties of a novel metal–organic framework templated by the large 1,1-dimethylhydrazinium cation. We analyse the steric hindrance-related properties.

Mechanism of Unusual Isosymmetric Order-Disorder Phase Transition in [Dimethylhydrazinium]Mn(HCOO)3 Hybrid Perovskite Probed by Vibrational Spectroscopy

“…3 mL) of 1,1-dimethylhydrazine dissolved in 10 mL of methanol with the addition of 160 mmol (7.25 mL) of HCOOH and the second, composed of 1 mmol (0.3619 g) of Mn(ClO 4 ) 2 •6H 2 O dissolved in 10 mL of methanol. Further details can be found in [2].…”

“…Further increase in the cation size caused by the presence of the second methyl group leads to complete suppression of non-centrosymmetric structures in [DMHy]Mn(HCOO) 3 , (DMHy + denotes 1,1-dimethylhydrazinium cation). This crystal, recently synthesized by us, exhibits unusual order-disorder PT among metal-formate hybrids [2]. In fact, [DMHy]Mn(HCOO) 3 is the first example of a formate-based perovskite that does not change the space group symmetry as a result of LT ordering.…”

“…3D hybrid metal-formate perovskites, a class of multifunctional materials described by the general formula [A]M II (HCOO) 3 , where A is an ammonium cation and M II denotes a divalent metal cation, caught the attention of materials scientists in a few recent years because of their unusual luminescent, [1,2] ferroelastic, [3,4] ferroelectric, [5][6][7] dielectric, [2,4,8] magnetic [2,9,10] or multiferroic [3,[11][12][13] properties. These properties originate from orderdisorder phase transitions (PTs) that enable utilizing them as molecular switches [14][15][16].…”

“…Therefore, we have decided to undertake similar studies for [DMHy]Mn(HCOO) 3 and compare its phonon properties to former compounds. Detailed temperature-dependent studies with small temperature increments allowed to obtain deeper insight into structural changes occurring in this compound at 244.4 K (283.0 K) on cooling (heating) [2] and to elucidate the main driving force of the PT. It is worth adding that the P2 1 /n-P2 1 /n isosymmetric PT is also interesting from the spectroscopic point of view because weak changes of vibrational selection rules are expected in spite of significant structural changes and the associated high change of entropy [2].…”

“…Detailed temperature-dependent studies with small temperature increments allowed to obtain deeper insight into structural changes occurring in this compound at 244.4 K (283.0 K) on cooling (heating) [2] and to elucidate the main driving force of the PT. It is worth adding that the P2 1 /n-P2 1 /n isosymmetric PT is also interesting from the spectroscopic point of view because weak changes of vibrational selection rules are expected in spite of significant structural changes and the associated high change of entropy [2]. Moreover, the isosymmetric and isostructural PTs occurring in the coordination polymers are still poorly understood [16,[22][23][24][25][26][27][28][29].…”