[Am]Mn(H2POO)3: A New Family of Hybrid Perovskites Based on the Hypophosphite Ligand

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.

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.

Synthesis of an Isostructural Series of 12-Coordinate Lanthanide Nitrate Hybrid Double Perovskites with Cubic Symmetry

In efforts to study the periodic chemical properties of the rare earth elements and their structural chemistry, a hybrid double perovskite phase A₂B'BX₆ with the formula ((CH₃)₄N)₂KLn(NO₃)₆ (Ln = La-Lu, Y ex. Pm) was synthesized that crystallizes in the cubic space group, Fm3̅m. This series was obtained via evaporative crystallization from a mixture of Ln(NO₃)₃, KNO₃, and (CH₃)₄N·NO₃ in a 1:1:2 ratio from either H₂O or 4.0 M HNO₃. In this double perovskite structure, the B site containing the lanthanide ion is coordinated by six bidentate nitrate ligands, with the distal N═O oxygen atoms coordinating the potassium on the B' site in an octahedral six-coordinate environment. The two remaining charge-compensating (CH₃)₄N⁺ cations occupy the interstitial voids in the lattice on the A site. This periodic series was characterized via single-crystal X-ray diffraction, powder X-ray diffraction, IR, and Raman spectroscopy. Emission spectra of the Eu complex indicate a phase transition to trigonal symmetry upon cooling. This series is unique as it represents a rare isostructural series spanning the entirety of the rare earth elements excluding promethium with homoleptic 12-coordinate rare earth metal ions.

Mechanochemically synthesised dicyanamide hybrid organic-inorganic perovskites, and their melt-quenched glasses

Here we present efficient and scalable mechanochemical formation of hybrid organic-inorganic perovskites of the form [TPrA][M(dca)₃] (M = Mn²⁺, Co²⁺) and the subsequent formation of their bulk melt-quenched glasses. In situ X-ray diffraction reveals direct, facile, and almost instantaneouos formation of both crystalline materials, while slow cooling limits recrystallisation in glasses. The glasses show good stability to acidic and basic aqueous solutions and display higher carbon dioxide uptakes than their crystalline precursors.

Principles of melting in hybrid organic-inorganic perovskite and polymorphic ABX3 structures

Four novel dicyanamide-containing hybrid organic-inorganic ABX₃ structures are reported, and the thermal behaviour of a series of nine perovskite and non-perovskite [AB(N(CN)₂)₃] (A = (C₃H₇)₄N, (C₄H₉)₄N, (C₅H₁₁)₄N; B = Co, Fe, Mn) is analyzed. Structure-property relationships are investigated by varying both A-site organic and B-site transition metal cations. In particular, increasing the size of the A-site cation from (C₃H₇)₄N → (C₄H₉)₄N → (C₅H₁₁)₄N was observed to result in a decrease in T _m through an increase in ΔS _f. Consistent trends in T _m with metal replacement are observed with each A-site cation, with Co < Fe < Mn. The majority of the melts formed were found to recrystallise partially upon cooling, though glasses could be formed through a small degree of organic linker decomposition. Total scattering methods are used to provide a greater understanding of the melting mechanism.

Above-Room-Temperature Ferroelastic Phase Transitions in Two Tetrafluoroborate-Based Hexagonal Molecular Perovskites

ABX₃-type molecular perovskites provide an important platform to tune phase transitions, via judiciously choosing A-, B-, and X-site components, to approach advanced functional materials for applications. Although tetrafluoroborate can act as X-site component to assemble ten instances of ABX₃ molecular perovskites, only two of them possess hexagonal perovskite structures. Herein, we report two tetrafluoroborate-based hexagonal molecular perovskites, A[Na(BF₄)₃], by judiciously choosing two different A-site cations: 1-methyl-1,4-diazabicyclo[2.2.2]octane-1,4-diium (Hmdabco²⁺) for 1 and 1-methylpiperazine-1,4-diium (H₂mpz²⁺) for 2. They have high-temperature phases in the same space group (P6₃/mmc) revealing highly disordered A-site cations. Upon cooling, 1 undergoes two-step P6₃/mmc ↔ P3̅c1 ↔ P2₁/n transitions at 344 and 338 K, respectively, including a ferroelastic one (3̅mF2/m) accompanied by a spontaneous strain of 0.013. In contrast, the smaller H₂mpz²⁺ cation with more adoptable conformations induces a one-step sharp P6₃/mmc ↔ P2₁/c ferroelastic transition (6/mmmF2/m(s)) at 418 K in 2, leading to more significant symmetry breaking and a considerable spontaneous strain of 0.129. This study provides important clues to modulate structural phase transitions by tuning diverse components for the multicomponent dense hybrid crystals.

Near-Infrared Phosphorescent Hybrid Organic-Inorganic Perovskite with High-Contrast Dielectric and Third-Order Nonlinear Optical Switching Functionalities

Hybrid organic-inorganic perovskites providing integrated functionalities for multimodal switching applications are widely sought-after materials for optoelectronics. Here, we embark on a study of a novel pyrrolidinium-based cyanide perovskite of formula (C4H10N)2KCr(CN)6, which displays thermally driven bimodal switching characteristics associated with an order-disorder phase transition. Dielectric switching combines two features important from an application standpoint: high permittivity contrast (Δε' = 38.5) and very low dielectric losses. Third-order nonlinear optical switching takes advantage of third-harmonic generation (THG) bistability, thus far unprecedented for perovskites and coordination polymers. Structurally, (C4H10N)2KCr(CN)6 stands out as the first example of a three-dimensional stable perovskite among formate-, azide-, and cyanide-based metal-organic frameworks comprising large pyrrolidinium cations. Its stability, reflected also in robust switching characteristics, has been tracked down to the Cr3+ component, the ionic radius of which provides a large enough metal-cyanide cage for the pyrrolidinium cargo. While the presence of polar pyrrolidinium cations leads to excellent switchable dielectric properties, the presence of Cr3+ is also responsible for efficient phosphorescence, which is remarkably shifted to the near-infrared region (770 to 880 nm). The presence of Cr3+ was also found indispensable to the THG switching functionality. It is also found that a closely related cobalt-based analogue doped with Cr3+ ions displays distinct near-infrared phosphorescence as well. Thus, doping with Cr3+ ions is an effective strategy to introduce phosphorescence as an additional functional property into the family of cobalt-cyanide thermally switchable dielectrics.

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=...

Hexanitrato complexes and hybrid double perovskites of Am3+ and Cm3+

Isostructural, homoleptic twelve-coordinate nitrato complexes of the 5f-ions Am and Cm are reported that occur as hybrid double perovskites.

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.

Melting of hybrid organic-inorganic perovskites

Several organic-inorganic hybrid materials from the metal-organic framework (MOF) family have been shown to form stable liquids at high temperatures. Quenching then results in the formation of melt-quenched MOF glasses that retain the three-dimensional coordination bonding of the crystalline phase. These hybrid glasses have intriguing properties and could find practical applications, yet the melt-quench phenomenon has so far remained limited to a few MOF structures. Here we turn to hybrid organic-inorganic perovskites-which occupy a prominent position within materials chemistry owing to their functional properties such as ion transport, photoconductivity, ferroelectricity and multiferroicity-and show that a series of dicyanamide-based hybrid organic-inorganic perovskites undergo melting. Our combined experimental-computational approach demonstrates that, on quenching, they form glasses that largely retain their solid-state inorganic-organic connectivity. The resulting materials show very low thermal conductivities (~0.2 W m^-1 K^-1), moderate electrical conductivities (10^-3-10^-5 S m^-1) and polymer-like thermomechanical properties.

Tilting and twisting in a novel perovzalate, K3NaMn(C2O4)3

A unique variant on the perovskite structure, K₃NaMn(C₂O₄)₃, has been identified with unconventional octahedral tilting, interpenetration of two topologically identical perovskite-like frameworks and an unusual, twisted oxalate ligand.

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.

Structural insights into a new family of three-dimensional thiocyanate-bridged molecular double perovskites

Four new three-dimensional thiocyanate-bridged molecular double perovskites with bent Cd–S–C angles in a narrow distribution range reveal highly distorted frameworks with a relatively strong structural rigidity.

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.

Pyrrolidinium-Based Cyanides: Unusual Architecture and Dielectric Switchability Triggered by Order-Disorder Process

Two three-dimensional metal–organic compounds of the formula Pyr₂KM(CN)₆, where M = Co, Fe and Pyr = pyrrolidinium ((CH₂)₄NH₂⁺), have been found to crystallize at room temperature in a monoclinic structure, space group P2₁/c. They are cyano-bridged compounds with an unprecedented type of architecture containing pyrrolidinium cations in the voids. The materials have been investigated by X-ray diffraction, dielectric, and spectroscopic methods as a function of temperature in order to determine their properties and the mechanism of the reversible phase transitions occurring at ca. 345–370 K. The phase transitions in both crystals are first order and are associated with a symmetry increase to a rhombohedral structure (space group R3®m) as well as a significant disorder of organic cations above T_c. On the basis of Raman scattering and IR spectroscopy it has been assumed that the phase transition in both crystals is triggered by thermally induced pseudorotation of the organic cation and large out-of-plane motions of its atoms followed by a “click-in” of the cyanide bridges. The materials have been proposed as possible switchable dielectrics due to their respective high differences in dielectric permittivities across the phase transition.

Two pyrrolidinium-based cyano-bridged compounds are described with reference to their dielectric properties, which can be switched by temperature. In addition, the mechanisms of the phase transitions are elucidated by X-ray diffraction and vibrational spectroscopy.

Phonon properties and mechanism of order-disorder phase transition in formamidinium manganese hypophosphite single crystal

The detailed temperature-dependent IR and Raman spectra were used to study and understand the mechanism of structural phase transition occurring at 175 K in manganese hypophosphite templated with formamidinium (FA⁺) ions, [FA]Mn(H₂POO)₃, which adopts a perovskite-like architecture. The structural transformation between the C2/c and the P2₁/c monoclinic phases has a complicated nature and is mainly driven by re-orientational motions of the FA⁺ cations but it is also accompanied by a significant distortion of the MnO₆ octahedral units as well as steric-forced changes of the PH₂ groups determining the off-center shifts of FA⁺ cations in the cages. The re-orientational motions of formamidinium cations at 175 K are followed by slight changes of their geometry and re-arrangement of hydrogen bonds (HBs). The strong temperature-dependences of bands corresponding to vibrations involving hydrogen bonding reveal the highly-dynamic character of this phase transition and strong nature of created HBs. The most pronounced changes are observed for the modes corresponding to the formamidinium cation, proving that the phase transition has an order-disorder character.

Tilts and shifts in molecular perovskites

A survey of the rigid unit modes in molecular perovskites is presented, showing how the prevalence of conventional tilts, unconventional tilts and columnar shifts vary across the different classes of molecular perovskites.

A new polar perovskite coordination network with azaspiroundecane as A-site cation

We report a new polar ABX₃ perovskite coordination network based on azaspiroundecane as A-site cation and dicyanamide as X-site anion.

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

Hybrid perovskites based on hypophosphite ligands constitute an emerging family of compounds exhibiting unusual structures and offering a platform for construction of novel functional materials. We report the synthesis, crystal structure, and magnetic and optical properties of novel undoped and HCOO⁻-doped manganese hypophosphite frameworks templated by methylhydrazinium cations. The undoped compound crystallizes in a three-dimensional perovskite-like orthorhombic structure, space group Pnma, with ordered organic cations located in windows between the perovskite cages expanding along the a-direction. Both conventional anti-phase tilting, unconventional in-phase tilting and columnar shifts in the a-direction are present. Doping with HCOO⁻ ions has a insignificant influence on the crystal structure but leads to a decrease of the unit cell volume. Magnetic studies indicate that these compounds order antiferromagnetically at T_N = 6.5 K. Optical studies indicate that they exhibit red photoluminescence under 266 nm excitation with the activation energy for thermal quenching of 98 and 65 meV for the undoped and doped sample, respectively. For the undoped sample, the emission lifetime reaches 5.05 ms at 77 K but it decreases to 62.26 μs at 300 K. The low value of the activation energy and huge temperature dependence of photoluminescence intensity suggest a high potential of these hypophosphites for non-contact temperature sensing.

The first perovskite-type hypophosphite-linked dense metal–organic framework exhibiting red emission and antiferromagnetic order at 6.5 K.

Hybrid Organic-Inorganic Antiperovskites

Substitution of A-site and/or X-site ions of ABX₃ -type perovskites with organic groups can give rise to hybrid perovskites, many of which display intriguing properties beyond their parent compounds. However, this method cannot be extended effectively to hybrid antiperovskites. Now, the design of hybrid antiperovskites under the guidance of the concept of Goldschmidt's tolerance factor is presented. Spherical anions were chosen for the A and B sites and spherical organic cations for the X site, and seven hybrid antiperovskites were obtained, including (F₃ (H₂ O)_x )(AlF₆ )(H₂ dabco)₃ , ((Co(CN)₆ )(H₂ O)₅ )(MF₆ )(H₂ dabco)₃ (M=Al³⁺ , Cr³⁺ , or In³⁺ ), (Co(CN)₆ )(MF₆ )(H₂ pip)₃ (M=Al³⁺ or Cr³⁺ ), and (SbI₆ )(AlF₆ )(H₂ dabco)₃ . These new structures reveal that all ions at A, B, and X sites of inorganic antiperovskites can be replaced by molecular ions to form hybrid antiperovskites. This work will lead to the synthesis of a large family of hybrid antiperovskites.

Mix and Match: Organic and Inorganic Ions in the Perovskite Lattice

Materials science evolves to a state where the composition and structure of a crystal can be controlled almost at will. Given that a composition meets basic requirements of stoichiometry, steric demands, and charge neutrality, researchers are now able to investigate a wide range of compounds theoretically and, under various experimental conditions, select the constituting fragments of a crystal. One intriguing playground for such materials design is the perovskite structure. While a game of mixing and matching ions has been played successfully for about 150 years within the limits of inorganic compounds, the recent advances in organic-inorganic hybrid perovskite photovoltaics have triggered the inclusion of organic ions. Organic ions can be incorporated on all sites of the perovskite structure, leading to hybrid (double, triple, etc.) perovskites and inverse (hybrid) perovskites. Examples for each of these cases are known, even with all three sites occupied by organic molecules. While this change from monatomic ions to molecular species is accompanied with increased complexity, it shows that concepts from traditional inorganic perovskites are transferable to the novel hybrid materials. The increased compositional space holds promising new possibilities and applications for the universe of perovskite materials.

Isostructural phase transition, quasielastic neutron scattering and magnetic resonance studies of a bistable dielectric ion-pair crystal [(CH3)2NH2]2KCr(CN)6

We have synthesised and characterised a novel organic-inorganic hybrid crystal, [(CH3)2NH2]2KCr(CN)6. The thermal DSC, TMA, DTG and DTA analyses indicate two solid-to-solid structural phase transitions (PTs). According to the X-ray diffraction experiments, the first PT at 220 K is isostructural, since it does not involve a change of the space group. This transition occurs between the states, where the (CH3)2NH2+ cations are orientationally disordered and ordered (frozen). The other reversible PT at 481 K leads to a melt-like phase similar to the one observed in plastic crystals or polar liquids. Dielectric spectroscopy has been used to characterise the switching properties of the dipole moments in the vicinity of the PTs. Continuous-wave electron paramagnetic resonance spectroscopy was employed to investigate the effect of ordering on the local environment of the Cr3+ ions. We have also applied the quasielastic neutron scattering (QENS) technique as well as 1H NMR spectroscopy to measure the dynamics of the (CH3)2NH2+ cations residing in the inorganic framework.

Structural, phonon, magnetic and optical properties of novel perovskite-like frameworks of TriBuMe[M(dca)3] (TriBuMe = tributylmethylammonium; dca = dicyanamide; M = Mn2+, Fe2+, Co2+, Ni2+)

Tributylmethylammonium metal dicyanamides exhibit huge caloric effects due to order–disorder phase transitions, and the Mn analogue shows orange emission under 420 nm excitation.

Polymorphism in M(H2PO2)3 (M = V, Al, Ga) compounds with the perovskite-related ReO3 structure

The connectivity of the ReO₃ structure is reproduced in a series of hypophosphite compounds, M(H₂PO₂)₃, where M = V, Al, Ga.

Raman and single-crystal X-ray diffraction evidence of pressure-induced phase transitions in a perovskite-like framework of [(C3H7)4N] [Mn(N(CN)2)3]

The [TPrA][Mn(dca)₃] perovskite shows highly anisotropic compression and the presence of three pressure-induced phase transitions near 0.4, 3 and 5 GPa into lower symmetry phases.

(H2dabco)[Na(BF4)3]: an ABX3-type inorganic–organic hybrid perovskite compound exhibiting dielectric switching above room-temperature

The (H₂dabco)[Na(BF₄)₃] undergoes a static-to-dynamic phase transition at 403/386 K. Crystal structure analysis reveals that H₂dabco²⁺ and/or BF₄⁻ undergo disordering.

Rational chemical doping of metal halide perovskites

Metal halide perovskites benefit from the combination of wide absorption, high carrier mobility, defect tolerance, moderate exciton binding energies, and versatility of solution processes, showing great promise in photovoltaics and optoelectronics. However, the issues of long-term instability and toxicity of lead are supposed to limit their further practical applications. Chemical doping of an impurity into metal halide perovskites was reported to be a relatively effective approach to solving these issues while providing additional tunable physical and chemical properties. In an attempt to boost the research field further, it is imperative to summarize the recent significant work on metal halide doped perovskites, disclosing the underlying structure-property relationships to provide useful insights into applications of these perovskites with high performance. In this review, we highlight the rational design of doped perovskites by both theoretical and experimental efforts as well as their potential application spanning various fields.

Mixed X-Site Formate-Hypophosphite Hybrid Perovskites

Following the recent discovery of a new family of hybrid ABX₃ perovskites where X=(H₂ POO)^- (hypophosphite), this work reports a facile synthesis for mixed X-site formate perovskites of composition [GUA]Mn(HCOO)_3-x (H₂ POO)_x , with two crystallographically distinct, partially ordered intermediate phases with x=0.84 and 1.53, corresponding to ca. 30 and 50 mol % hypophosphite, respectively. These phases are characterised by single-crystal XRD and solid-state NMR spectroscopy, and their magnetic properties are reported.

Recipes for improper ferroelectricity in molecular perovskites

The central goal of crystal engineering is to control material function via rational design of structure. A particularly successful realisation of this paradigm is hybrid improper ferroelectricity in layered perovskite materials, where layering and cooperative octahedral tilts combine to break inversion symmetry. However, in the parent family of inorganic ABX₃ perovskites, symmetry prevents hybrid coupling to polar distortions. Here, we use group-theoretical analysis to uncover a profound enhancement of the number of improper ferroelectric coupling schemes available to molecular perovskites. This enhancement arises because molecular substitution diversifies the range of distortions possible. Not only do our insights rationalise the emergence of polarisation in previously studied materials, but we identify the fundamental importance of molecular degrees of freedom that are straightforwardly controlled from a synthetic viewpoint. We envisage that the crystal design principles we develop here will enable targeted synthesis of a large family of new acentric functional materials.

Hypophosphite hybrid perovskites: a platform for unconventional tilts and shifts

Following the recent discovery of the [A]Mn(H₂POO)₃ perovskite family, we report the A = dimethylammonium member. We then enumerate the unusual octahedral tilting and shifting observed across this perovskite family.

Temperature-dependent studies of a new two-dimensional cadmium dicyanamide framework exhibiting an unusual temperature-induced irreversible phase transition into a three-dimensional perovskite-like framework

TPrACd can be grown in both layered and perovskite-like architectures. The layered polymorph transforms irreversibly to the perovskite one at 389 K.