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

Jan Albert Zienkiewicz,Edyta Kucharska,Maciej Ptak

doi:10.3390/ma14143984

Jan Albert Zienkiewicz, Edyta Kucharska + Show 1 more

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https://doi.org/10.3390/ma14143984

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Abstract

[DMHy]Mn(HCOO)3 (DMHy+ = dimethylhydrazinium cation) is an example of an organic–inorganic hybrid adopting perovskite-like architecture with the largest organic cation used so far in the synthesis of formate-based hybrids. This compound undergoes an unusual isosymmetric phase transition at 240 K on heating. The mechanism of this phase transition has a complex nature and is mainly driven by the ordering of DMHy+ cations and accompanied by a significant distortion of the metal–formate framework in the low temperature (LT) phase. In this work, the Density Functional Theory (DFT) calculations and factor group analysis are combined with experimental temperature-dependent IR and Raman studies to unequivocally assign the observed vibrational modes and shed light on the details of the occurring structural changes. The spectroscopic data show that this first-order phase transition has a highly dynamic nature, which is a result of balanced interplay combining re-arrangement of the hydrogen bonds and ordering of DMHy+ cations. The tight confinement of organic cations forces simultaneous steric deformation of formate ions and the MnO6 octahedra.

Highlights

We propose an assignment of the observed IR and Raman bands based on literature data for Hy+ and MHy+ analogues supported by Density Functional Theory (DFT) calculations reported in this paper for dimethylhydrazine molecule (DMHy)+ cation
Crystal Structure and Geometry Optimization. Both low temperature (LT) and HT phases of [DMHy]Mn(HCOO)3 are described by the P21 /n monoclinic symmetry [2]
We have studied phonon properties of manganese–formate framework templated by DMHy+ cations combining the DFT calculations and the temperature-dependent IR

Summary

Introduction

Inorganic hybrid adopting perovskite-like architecture with the largest organic cation used so far in the synthesis of formate-based hybrids. This compound undergoes an unusual isosymmetric phase transition at 240 K on heating. The mechanism of this phase transition has a complex nature and is mainly driven by the ordering of DMHy+ cations and accompanied by a significant distortion of the metal–formate framework in the low temperature (LT) phase. Since the hydrazinium cation (Hy+ ) has a small size, [Hy]MII (HCOO) compounds with MII = Mn2+ , Zn2+ and Fe2+ can adopt two types of structure, namely 412 ·63 perovskite-like with cubic cavities or 49 ·63 chiral with hexagonal channels [17,18,19].

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