Novel hypophosphite hybrid perovskites of [CH3NH2NH2][Mn(H2POO)3] and [CH3NH2NH2][Mn(H2POO)2.83(HCOO)0.17] exhibiting antiferromagnetic order and red photoluminescence

Raman study of pressure-induced phase transitions in imidazolium manganese- hypophosphite hybrid perovskite

By using Raman spectroscopy, we demonstrate that [IM]Mn(H₂POO)₃ is a highly compressible material that undergoes three pressure-induced phase transitions. Using a diamond anvil cell we performed high-pressure experiments up to 7.1 GPa, using paraffin oil as the compression medium. The first phase transition, which occurs near 2.9 GPa, leads to very pronounced changes in the Raman spectra. This behavior indicates that this transition is associated with very large reconstruction of the inorganic framework and collapse of the perovskite cages. The second phase transition, which occurs near 4.9 GPa, is associated with subtle structural changes. The last transition takes place near 5.9 GPa and it leads to further significant distortion of the anionic framework. In contrast to the anionic framework, the phase transitions have weak impact on the imidazolium cation. Pressure dependence of Raman modes proves that compressibility of the high-pressure phases is significantly lower compared to the ambient pressure phase. It also indicates that the contraction of the MnO₆ octahedra prevails over that of the imidazolium cations and hypophosphite linkers. However, compressibility of MnO₆ strongly decreases in the highest pressure phase. Pressure-induced phase transitions are reversible.

Synthesis, crystal structure and phase transitions of novel hybrid perovskite: bis(1,2-diaminopropane) di-μ-chloro-bis[diaquadichloromanganate(II)] dichloride

Single crystals of bis(1,2-diaminepropane) di-μ-chloro-bis[diaquadichloromanganate(II)] dichloride have been prepared by evaporation from ethanoic solution. The triclinic X-ray crystal structure is built as layers of centrosymmetric dimers of [Mn(Cl)4(H2O)2]2- octahedra and 1,2-diaminopropane. The inorganic part consists of Mn octahedra sharing one edge and distributed in the basal ac plane along the a direction. These doubly negative charged layers are separated along the b axis by a positively charged diamine propane layer. One Cl- anion contributes to the electroneutrality of the crystal interacting with both inorganic - through a hydrogen bond network to the two water molecules coordinated to Mn - and organic layers via the NH3+ ammonium group. Differential scanning calorimetry shows two endothermic main peaks at T = 366 K and T = 375 K related to the release of the water molecules. The resulting dehydrated material is C-centered monoclinic as shown by powder X-ray diffraction.

Luminescence and Dielectric Switchable Properties of a 1D (1,1,1-Trimethylhydrazinium)PbI3 Hybrid Perovskitoid

The synthesis and investigation of the physicochemical properties of a novel one-dimensional (1D) hybrid organic-inorganic perovskitoid templated by the 1,1,1-trimethylhydrazinium (Me₃Hy⁺) cation are reported. (Me₃Hy)[PbI₃] crystallizes in the hexagonal P6₃/m symmetry and undergoes two phase transitions (PTs) during heating (cooling) at 322 (320) and 207 (202) K. X-ray diffraction data and temperature-dependent vibrational studies show that the second-order PT to the high-temperature hexagonal P6₃/mmc phase is associated with a weak change in entropy and is related to weak structural changes and different confinement of cations in the available space. The second PT to the low-temperature orthorhombic Pbca phase that corresponds to the high change in entropy and dielectric switching is associated with an ordering of the trimethylhydrazinium cations, re-arrangement and strengthening of hydrogen bonds, and slightly shifted lead-iodide octahedral chains. The high-pressure Raman data revealed two additional PTs, one between 2.8 and 3.2 GPa, related to the symmetry decrease, ordering of the cations, and inorganic chain distortion, and the other in the 6.4-6.8 GPa range related to the partial and reversible amorphization. Optical studies revealed that (Me₃Hy)[PbI₃] has a wide band gap (3.20 eV) and emits reddish-orange excitonic emission at low temperatures with an activation energy of 65 meV.

Effect of Organic Cation on Optical Properties of [A]Mn(H2POO)3 Hybrid Perovskites

Hybrid organic-inorganic compounds crystallizing in a three-dimensional (3D) perovskite-type architecture have attracted considerable attention due to their multifunctional properties. One of the most intriguing groups is perovskites with hypophosphite linkers. Herein, the optical properties of six hybrid hypophosphite perovskites containing manganese ions are presented. The band gaps of these compounds, as well as the luminescence properties of the octahedrally coordinated Mn2+ ions associated with the 4T1g(G) → 6A1g(S) transition are shown to be dependent on the organic cation type and Goldschmidt tolerance factor. Thus, a correlation between essential structural features of Mn-based hybrid hypophosphites and their optical properties was observed. Additionally, the broad infrared luminescence of the studied compounds was examined for potential application in an indoor lighting system for plant growth.

Structural, magnetic and photoluminescent properties of new hybrid hypophosphites: discovery of the first noncentrosymmetric and two cobalt-based members

Hybrid organic-inorganic perovskites comprising hypophosphite ligands are emerging functional materials exhibiting magnetic, photoluminescence, negative thermal expansion and negative linear compressibility behaviour. This work reports five novel hypophosphite perovskites, [A]M(H2POO)3 (A=...

The cation-dependent structural, magnetic and optical properties of a family of hypophosphite hybrid perovskites

Hypophosphite hybrid perovskites have recently received widespread attention due to their diverse structural and magnetic properties, negative thermal expansion and photoluminescence behaviour. Herein, we report two new three-dimensional hybrid perovskites containing unusually large organic cations, pyrrolidinium and 2-hydroxyethylammonium. We report the crystal structures of these new manganese-hypophosphite frameworks and their magnetic and optical properties. We also report the magnetic and optical properties of two previously discovered analogues, dimethylammonium and imidazolium manganese hypophosphites. Both new compounds crystallize in a monoclinic structure, space group P2₁/n, with ordered organic cations at room temperature. Magnetic studies show that all studied compounds are examples of canted antiferromagnets but the weak ferromagnetic contribution and the ordering temperature are significantly modulated by the type of organic cation located in the cavity of the framework. We discuss the origin of this behaviour. Upon ultraviolet excitation, all compounds exhibit broadband photoluminescence associated with the ⁴T_1g(G) → ⁶A_1g(S) transition of octahedrally coordinated Mn²⁺ ions. The position of the PL band depends on the type of organic cation, being the most blue-shifted for the imidazolium analogue (646 nm) and the most red-shifted for the pyrrolidinium counterpart (689 nm). The most interesting property of the studied hypophosphites is, however, the strong temperature dependence of the photoluminescence intensity, suggesting the possible application of these compounds in non-contact optical thermometry.

Tilt and shift polymorphism in molecular perovskites

Molecular perovskites, i.e. ABX₃ coordination polymers with a perovskite structure, are a chemically diverse material platform for studying fundamental and applied materials properties such as barocalorics and improper ferroelectrics. Compared to inorganic perovskites, the use of molecular ions on the A- and X-site of molecular perovskites leads to new geometric and structural degrees of freedom. In this work we introduce the concept of tilt and shift polymorphism, categorising irreversible perovskite-to-perovskite phase transitions in molecular perovskites. As a model example we study the new molecular perovskite series [(nPr)₃(CH₃)N]M(C₂N₃)₃ with M = Mn²⁺, Co²⁺, Ni²⁺, and nPr = n-propyl, where different polymorphs crystallise in the perovskite structure but with different tilt systems depending on the synthetic conditions. Tilt and shift polymorphism is a direct ramification of the use of molecular building units in molecular perovskites and as such is unknown for inorganic perovskites. Given the role of polymorphism in materials science, medicine and mineralogy, and more generally the relation between physicochemical properties and structure, the concept introduced herein represents an important step in classifying the crystal chemistry of molecular perovskites and in maturing the field.

Cadmium and manganese hypophosphite perovskites templated by formamidinium cations: dielectric, optical and magnetic properties

The first cadmium hypophosphite perovskite exhibiting reddish-orange emission, glass-like behaviour and order–disorder phase transition.

Vibrational Properties and DFT Calculations of Perovskite-Type Methylhydrazinium Manganese Hypophosphite

Recently discovered hybrid perovskites based on hypophosphite ligands are a promising class of compounds exhibiting unusual structural properties and providing opportunities for construction of novel functional materials. Here, we report for the first time the detailed studies of phonon properties of manganese hypophosphite templated with methylhydrazinium cations ([CH3NH2NH2][Mn(H2PO2)3]). Its room temperature vibrational spectra were recorded for both polycrystalline sample and a single crystal. The proposed assignment based on Density Functional Theory (DFT) calculations of the observed vibrational modes is also presented. It is worth noting this is first report on polarized Raman measurements in this class of hybrid perovskites.