Raman Spectroscopy Studies on the Barocaloric Hybrid Perovskite [(CH3)4N][Cd(N3)3]

The wondrous world of ABX3 molecular perovskites

The substitution of atoms with molecular building blocks to form hybrid organic-inorganic networks has been an important research theme for several decades. ABX3 molecular perovskites (MolPs) are a subclass of hybrid networks, adopting the perovskite structure with cationic and anionic molecules on the A-site and X-site. MolPs such as ((CH3)2NH2)Zn(HCOO)3 or ((n-C3H7)4N)Mn(C2N3)3 show a range of fascinating structure-chemical properties, including temperature-driven phase transitions that include a change of polarity as interesting for ferroelectrics, pressure-driven order-disorder phase transitions as interesting for barocaloric solid-state refrigeration, and most recently, melting-behaviour before decomposition with subsequent glass formation after cooling. In this feature article, we take a more personal perspective, overviewing the field's current state and outlining future directions. We start by comparing the MolPs' structural chemistry with their inorganic parents, a comparison that helps us identify opportunities for material design. After discussing the MolPs' potential as barocalorics, ferroelectrics, and in the area of glasses, we outline some challenges that lie ahead. Beyond their relevance as a hybrid analogue of inorganic perovskites, we find that MolPs' chemical parameter space provides exciting opportunities for systematically developing design guidelines for functional materials.

The crucial role of stability of intercalating agent for DNA binding studies in DMSO/water system

In recent years, extensive research has been directed towards understanding the interactions between various zinc complexes with DNA, specifically delving into their intercalation and binding behaviors. The binding of zinc complexes to DNA is particularly intriguing due to their distinctive intercalating capabilities. This study unveils a remarkable phenomenon observed with a specific Zn complex, ([B-Zn-N3], where B is a Schiff base ligand), during DNA intercalation investigations in the popular DMSO-Water binary solvent mixture. An unanticipated observation revealed time-dependent changes in the UV-visible absorption spectroscopic studies, coupled with the existence of an isosbestic point. This observation questions the stability of the intercalating agent itself during the intercalation process. The emergence of a decomposed product during the intercalation study has been confirmed through various analytical techniques, including CHN analysis, MALDI mass, XPS, Raman spectroscopy, and Powder XRD. The change in the chemical species on intercalation is further substantiated by theoretical studies, adding depth to our understanding of the intricate dynamics at play during DNA intercalation with the [B-Zn-N3] complex in the DMSO-Water system.

Order-disorder phase transition and molecular dynamics in the hybrid perovskite [(CH3)3NH][Mn(N3)3]

We present a temperature-dependent Raman scattering study of a [(CH₃)₃NH][Mn(N₃)₃] hybrid organic-inorganic azide-perovskite, in which we have analysed in detail the wavenumber and full width at half-maximum (FWHM) of lattice modes and internal modes of the NC₃ skeleton, N₃^- and CH₃ molecular groups. In general, the modes exhibited unusual behaviour during the phase transitions, including discontinuity in the phonon wavenumber, bandwidth, and unconventional shifts upon temperature variation. Spectral features on heating reveal the absence of significant distortions in the NC₃ skeleton and a relatively restricted order-disorder process of the TrMA⁺ cations. On the other hand, linewidth anomalies of the δNC₃ and ν_asNC₃ modes have been attributed to the molecular dynamics of encapsulated cations. The unconventional blue shift of the symmetric stretching modes of azide ligands indicates the weakening of the intermolecular interactions between the TrMA⁺ cations and azido-bridges, and the strengthening of the intramolecular bonds. Additionally, we have used differential scanning calorimetry to confirm the subtle monoclinic to monoclinic (P2₁/c → C2/c) phase transition at around 330 K; and the phase transition to trigonal structure (R3¯m) above 359 K, whose associated entropy variation turns to be |ΔS| ∼ 22.3 J·kg^-1 K^-1 and displays a barocaloric (BC) tunability |δTt/δP| ∼ 3.17 K kbar^-1, according to our estimations using the Clausius-Clapeyron method. Although the obtained values of entropy change and BC tunability are very close to those reported on formate-perovskites and other important caloric materials, those parameters are much lower than the giant entropy change of ∼80 Jkg^-1 K^-1 and large BC tunability ∼12 K kbar^-1 observed for the analogue azide-perovskite [(CH₃)₄N][Mn(N₃)]₃ (TMAMnN₃). Very interestingly, our combined study shed light to understand such different behaviour, as they reveal that the hydrogen bonds created between the TrMA⁺ cations and the framework prevent an extensive order-disorder process that is needed to obtain large entropy changes and large BC coefficients as it occurs in the case of related azide-perovskites with no H-bonds between the A cations (for example TMA) and the framework.