Disorder–order transitions in the perovskite metal–organic frameworks [(CH₃)₂NH₂][M(HCOO)₃] at high pressure

Abstract

Compression of dimethylammonium metal formates results in distorted metal formate frameworks and loss of dynamic disorder of dimethylammonium simultaneously.

Stability and flexibility of heterometallic formate perovskites with the dimethylammonium cation: pressure-induced phase transitions

“…The high-pressure effect on perovskite-like MOFs has been studied previously using Raman spectroscopy and X-ray diffraction for the DMAM II family (M II =Cd, 25 Mg, 25 Mn, 26,27 Fe 27 and Cu 27 ). Raman spectroscopy showed the presence of three phase transitions for DMAMg and DMAMn at 2.2 GPa, 4.0 GPa, and 5.6 GPa as well as at 2.1 GPa, 4.1 GPa, and 6.7 GPa, respectively, while only two phase transitions were found for DMACd, in the 1.2-2.0 GPa range and at 3.6 GPa.…”

“…25,26 The high-pressure X-ray diffraction studies only indicated the presence of one phase transition for DMAMn, in the 5.5-5.6 GPa range resulting from the transformation from ambient-pressure trigonal 3 to triclinic 1 symmetry. 27 The absence of the remaining two transitions was explained by their character, i.e. it was assumed that they result from the change of local symmetry, 27 which would be better visible using vibrational methods.…”

“…27 The absence of the remaining two transitions was explained by their character, i.e. it was assumed that they result from the change of local symmetry, 27 which would be better visible using vibrational methods.…”

“…The pressure of the last phase transition, which corresponds to the amorphization of the structures, is higher in both the DMAMg and DMAMn compounds than in DMANaCr, but slightly lower for DMACd. [25][26][27] To compare the flexibility (deformation ability) of heterometallic MOFs and divalent-formate frameworks the following factors should be taken into account; the pressure of phase transition(s), the number of transitions, the pressure of amorphization and the values of the pressure coefficients (α). The first three factors suggest that the structures of AmNaCr and ImNaCr are more flexible when compared to their divalentmetal analogues.…”

Tilts and shifts in molecular perovskites

“…[(CH 3 ) 2 NH 2 ]MnIJH 2 POO) 3 (ref. 41) and the triclinic high-pressure phase of [(CH 3 ) 2 NH 2 ]FeIJHCOO)3 ,42 yet are normally very weak. As the concept of "rigid units" is less valid in very distorted structures with low symmetry, this approach is perhaps less meaningful for such compounds.…”