Effect of solvent, temperature and pressure on the stability of chiral and perovskite metal formate frameworks of [NH₂NH₃][M(HCOO)₃] (M = Mn, Fe, Zn)

Abstract

We report the synthesis, crystal structure, and thermal, Raman, infrared and magnetic properties of [NHNH][M(HCOO)] (HyM) compounds (M = Mn, Zn, Fe). Our results show that synthesis from methanol solution leads to perovskite polymorphs while that from 1-methyl-2-pyrrolidinone or its mixture with methanol allows obtaining chiral polymorphs. Perovskite HyFe, chiral HyFe and chiral HyMn undergo phase transitions at 347, 336 and 296 K, respectively, with symmetry changes from Pnma to Pna2, P6 to P222 and P6 to P2. X-ray diffraction and Raman studies show that the phase transitions are governed by dynamics of the hydrazinium ions. Low-temperature magnetic studies show that these compounds exhibit magnetic ordering below 9-12.5 K. Since the low-temperature structures of chiral HyMn and perovskite HyFe are polar, these compounds are possible multiferroic materials. We also report high-pressure Raman scattering studies of chiral and perovskite HyZn, which show much larger stiffness of the latter phase. These studies also show that the ambient pressure polar phases are stable up to at least 1.4 and 4.1 GPa for the chiral and perovskite phase, respectively. Between 1.4 and 2.0 GPa (for chiral HyZn) and 4.1 and 5.2 GPa (for perovskite HyZn) pressure-induced transitions are observed associated with changes in the zinc-formate framework. Strong broadening of Raman bands and the decrease in their number for the high-pressure phase of chiral HyZn suggest that this phase is disordered and has higher symmetry than the ambient pressure one.

Raman‐scattering studies of pressure‐induced phase transitions in perovskite‐like acetamidninium manganese formate

“…These increased interactions are often strong enough to cause deformation of the metal formate framework, leading to pressure‐induced phase transitions. Phase transitions associated with distortion of metal formate framework and decrease of the crystal symmetry, were reported for [(CH 2 ) 3 NH 2 ][Zn(HCOO) 3 ], [ND 4 ][Zn(DCOO) 3 ], chiral [NH 2 NH 3 ][Zn(HCOO) 3 ], perovskite [NH 2 NH 3 ][Zn(HCOO) 3 ], [C 3 N 2 H 5 ][Mg(HCOO) 3 ], [NH 3 (CH 2 ) 4 NH 3 ][Zn 2 (HCOO) 6 ], [(CH 3 ) 2 NH 2 ][Mg(HCOO) 3 ], [(CH 3 ) 2 NH 2 ][Cd(HCOO) 3 ], and [(CH 3 ) 2 NH 2 ][Mn(HCOO) 3 ] at 0.4, 1.1, 2, 5.2, 3, 4.1, 2.2 (4.0), 2 (3.6), and 2.1 (4.1) . Upon further increase of pressure, the amine‐formate interactions exhibit further increase, and they may lead to further distortion of the framework and changes in the structure of the protonated amine itself.…”

“…For instance, it has been shown that application of pressure may lead to enhancement of ferroelectric properties or its suppression . Furthermore, application of pressure may lead to discovery of novel polymorphs that are not thermodynamically stable at ambient conditions . We have decided, therefore, to study high‐pressure behaviour of recently discovered acetamidinium manganese formate ([CH 3 C(NH 2 ) 2 ][Mn(HCOO) 3 ], AceMn), using Raman spectroscopy because this method is well‐known to be a very valuable tool in high‐pressure studies due to its sensitivity to changes in dynamics and structure of molecular units …”

“…[16] In the year 2009, multiferroic properties have been discovered in dimethylammonium manganese formate, [17] and this discovery promoted broad interest in search for new formate frameworks that show such properties. Up to now, multiferroic properties were discovered for a few other formate frameworks of general formula [cat][M(HCOO) 3 ] (M = Mn,Ni,Co,Fe) with cat = NH 4 + , [18] hydrazinium, [19] methylammonium [20] , and methylhydrazinium. [21] They were also predicted theoretically for ethylammonium and guanidinium analogues.…”

“…[24][25][26] The known formates have been extensively studied in a broad temperature range, and these studies showed that majority of them undergo phase transitions associated with orientational ordering of organic cations located in the cavities of the framework. [1,2,[7][8][9]14,[17][18][19][20][21] Pressure is another thermodynamic parameter that can help to better understand structure-property relationship in this class of compounds. [19,21,[26][27][28][29][30][31][32][33][34][35] For instance, it has been shown that application of pressure may lead to enhancement of ferroelectric properties [27] or its suppression.…”

Vibrational investigation of pressure‐ and temperature‐induced phase transitions in metal formates templated by ethylammonium ions

“…As a consequence, an investigation of behavior of MOFs in response to this external stimulus is necessary, especially from the application point of view. Up to date, a few papers reported high pressure studies of chiral, perovskite and niccolite metal formate frameworks. These studies revealed presence of pressure‐induced transformations and negative linear compressibility for some compounds.…”