Tilts and shifts in molecular perovskites

Boström, Hanna L. B.

doi:10.1039/c9ce01950b

Cited by 40 publications

(59 citation statements)

References 72 publications

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“…There are very few examples of perovskites with complex tilts, 60,61 and perhaps the best known is LiNbO 3 , which forms phases possessing tilts with periodicities of four (S-phase) and six (R-phase) unit cells along a single axis. 36 Complex tilting has also been observed in molecular perovskites, 46 with incommensurate tilting discovered in Me 2 NH 2 {Co(HCO 2 ) 3 } 62 and complex tilts along multiple axes in Me 2 NH 2 {Mn(H 2 PO 2 ) 3 } 47 . In both cases the tilts are unconventional as they are formed from shifts and/or out-of-phase tilts (where adjacent octahedra tilt in the same sense).…”

Section: Complex Tiltsmentioning

confidence: 91%

“…Although the tolerance factor approach explains which molecular AMX 3 frameworks are likely to crystallise with a perovskite structure, 8,9 it does not account for either the magnitudes or kinds of framework distortions observed. 46,47 For example, in the series of formate perovskites A{Mn(HCO 2 ) 3 } where A + = Rb + 48 , CH 3 NH 3 49 , (CH 3 ) 2 NH 2 50 and (CH 2 ) 3 NH 51 (arranged in increasing size of A + /increasing τ), there is no systematic trend in the size or pattern of the octahedral tilting, respectively:…”

Section: Coupling Between A-site Occupational Order and Octahedral Timentioning

confidence: 99%

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Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

Lee¹,

Ling²,

Argent³

et al. 2020

Preprint

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We report four new A-site vacancy ordered thiocyanate double double perovskites,A1􀀀xfNi[Bi(SCN)6]1􀀀x3 }, A = K+, NH4+, CH3(NH3)+ (MeNH3+) and C(NH2)3+ (Gua+), including the first examples of thiocyanate perovskites containing organic A-site cations. We show, using a combination of X-ray and neutron diffraction, that the structure of these frameworks depends on the A-site cation, and that these frameworks possess complex vacancy-ordering patterns and cooperative octahedral tilts distinctly different from atomic perovskites. Density functional theory calculations uncover the energetic origin of these complex orders and allow us to propose a simple rule to predict favoured A-site cation orderings for a given tilt sequence. We use these insights, in combination with symmetry mode analyses, to show that these complex orders offer a new route to non-centrosymmetric perovskites which render them as excellent candidates forpiezo- and ferroelectric applications.

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Section: Complex Tiltsmentioning

confidence: 91%

Section: Coupling Between A-site Occupational Order and Octahedral Timentioning

confidence: 99%

Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

Lee¹,

Ling²,

Argent³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“… 32 The linker shape may also guide the topology of the system and the propensity for distortions. 33 Hence, of the three site types in molecular frameworks, it is the X-site that offers the richest playground for tuning structure and function.…”

Section: Compositions Of Molecular Frameworkmentioning

confidence: 99%

“… 1 , 4 As for unconventional tilts, columnar shifts are frequently observed in frameworks with azide or dicyanamide ligands [ Figure 3 (a)]. 33 …”

Section: Columnar Shifts Breathing and Loop Movesmentioning

confidence: 99%

“…There will also be many other degrees of freedom not covered in this brief Account that are nonetheless worthy of exploration. Examples include the twist modes of paddlewheel units, 71 protonation states of organic linkers, 72 binding modes, 33 and the topological degrees of freedom associated with bond rearrangements; 73 there will be many others.…”

Section: Future Directionsmentioning

confidence: 99%

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Hybrid Perovskites, Metal–Organic Frameworks, and Beyond: Unconventional Degrees of Freedom in Molecular Frameworks

Boström

Goodwin

2021

Acc. Chem. Res.

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Conspectus The structural degrees of freedom of a solid material are the various distortions most straightforwardly activated by external stimuli such as temperature, pressure, or adsorption. One of the most successful design strategies in materials chemistry involves controlling these individual distortions to produce useful collective functional responses. In a ferroelectric such as lead titanate, for example, the key degree of freedom involves asymmetric displacements of Pb 2+ and Ti 4+ cations; it is by coupling these together that the system as a whole interacts with external electric fields. Collective rotations of the polyhedral units in oxide ceramics are another commonly exploited distortion, driving anomalous behavior such as negative thermal expansion—the counterintuitive phenomenon of volume contraction on heating. An exciting development in the field has been to take advantage of the interplay between different distortion types: generating polarization by combining two different polyhedral rotations, for example. In this way, degrees of freedom act as geometric “elements” that can themselves be combined to engineer materials with new and interesting properties. Just as the discovery of new chemical elements quite obviously diversified chemical space, we might expect that identifying new and different types of structural degrees of freedom to be an important strategy for developing new kinds of functional materials. In this context, the broad family of molecular frameworks is emerging as an extraordinarily fertile source of new and unanticipated distortion types, the vast majority of which have no parallel in the established families of conventional solid-state chemistry. Framework materials are solids whose structures are assembled from two fundamental components: nodes and linkers. Quite simply, linkers join the nodes together to form scaffolding-like networks that extend from the atomic to the macroscopic scale. These structures usually contain cavities, which can also accommodate additional ions for charge balance. In the well-established systems—such as lead titanate—node, linker, and extra-framework ions are all individual atoms (Ti, O, and Pb, respectively). But in molecular frameworks, at least one of these components is a molecule. In this Account, we survey the unconventional degrees of freedom introduced through the simple act of replacing atoms by molecules. Our motivation is to understand the role these new distortions play (or might be expected to play) in different materials properties. The various degrees of freedom themselves—unconventional rotational, translational, orientational, and conformational states—are summarized and described in the context of relevant experimental examples. The much-improved prospect for generating emergent functionalities by combining these new distortion types is then discussed. We highlight a number of directions for future research—including th...

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Designing Geometric Degrees of Freedom in ReO₃‐Type Coordination Polymers

Bürger

Hemmer

Mayer

et al. 2022

Adv Funct Materials

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Engineering the interplay of structural degrees of freedom that couple to external stimuli such as temperature and pressure is a powerful approach for material design. New structural degrees of freedom expand the potential of the concept, and coordination polymers as a chemically versatile material platform offer fascinating possibilities to address this challenge. Here, we report a new class of perovskite-like AB 2 X 6 coordination polymers based on a [BX 3 ] − ReO 3 -type host network ([Mn(C 2 N 3 ) 3 ] − ), in which the spatial orientation of divalent A 2+ cations ([R 3 N(CH 2 ) n NR 3 ] 2+ ) with separated charge centers that bridge adjacent ReO 3 -cavities is introduced as a new geometric degree of freedom. Herringbone and head-to-tail order pattern of [R 3 N(CH 2 ) n NR 3 ] 2+ cations are obtained by varying the separator length n and, together with distortions of the pseudocubic [BX 3 ] − network, they determine the materials' stimuli-responsive behavior such as counterintuitive large negative compressibility and uniaxial negative thermal expansion. This new family of coordination polymers highlights the chemists' capabilities of designing matter on a molecular level to address macroscopic material functionality and underpins the opportunities of the design of structural degrees of freedom as a conceptual framework for rational material synthesis in the future.

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Tilts and shifts in molecular perovskites

Abstract: 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.

Cited by 40 publications

References 72 publications

Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

Hybrid Perovskites, Metal–Organic Frameworks, and Beyond: Unconventional Degrees of Freedom in Molecular Frameworks

Designing Geometric Degrees of Freedom in ReO₃‐Type Coordination Polymers

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Tilts and shifts in molecular perovskites

Abstract: 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.

Cited by 40 publications

References 72 publications

Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

Controlling Multiple Orderings in Metal Thiocyanate Molecular Perovskites Ax{Ni[Bi(SCN)6]}

Hybrid Perovskites, Metal–Organic Frameworks, and Beyond: Unconventional Degrees of Freedom in Molecular Frameworks

Designing Geometric Degrees of Freedom in ReO3‐Type Coordination Polymers

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Designing Geometric Degrees of Freedom in ReO₃‐Type Coordination Polymers