Pedal motion or static disorder in single-component solids containing imine groups is demonstrated. Unique solid-state behaviors including colossal biaxial positive thermal expansion in one solid and a temperature-dependent phase transition in another are discussed. Imines exhibit torsional flexibility, which differs from the isoelectronic azo and olefin groups and influences solid-state behaviors.
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Colossal Anisotropic Thermal Expansion in a Diazo‐Functionalized Compound with Switchable Solid‐State Behavior
Achieving substantial anisotropic thermal expansion (TE) in solid‐state materials is challenging as most materials undergo volumetric expansion upon heating. Here, we describe colossal, anisotropic TE in crystals of an organic compound functionalized with two azo groups. Interestingly, the material exhibits distinct and switchable TE behaviors within different temperature regions. At high temperature, two‐dimensional, area zero TE and colossal, positive linear TE (α=211 MK−1) are attained due to dynamic motion, while at low temperature, moderate positive TE occurs in all directions. Investigation of the solid‐state motion showed the change in enthalpy and entropy are quite different in the two temperature regions and solid‐state NMR experiments support motion in the solid. Cycling experiments demonstrate that the solid‐state motions and TE behaviors are completely reversible. These results reveal strategies for designing significant anisotropic and switchable behaviors in solid‐state materials.
more » « less- Award ID(s):
- 2045506
- PAR ID:
- 10496500
- Publisher / Repository:
- Wiley-VCH GmbH
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 62
- Issue:
- 33
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- e202306198
- Subject(s) / Keyword(s):
- Anisotropic Thermal Expansion Azo Compounds Crystal Engineering Solid-State Motion Switchable Behaviors
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Control over thermal expansion (TE) behaviors in solid materials is often accomplished by modifying the molecules or intermolecular interactions within the solid. Here, we use a mixed cocrystal approach and incorporate molecules with similar chemical structures, but distinct functionalities. Development of mixed cocrystals is at a nascent stage, and here we describe the first mixed cocrystals sustained by one‐dimensional halogen bonds. Within each mixed cocrystal, the halogen‐bond donor is fixed, while the halogen‐bond acceptor site contains two molecules in a variable ratio. X‐ray diffraction demonstrates isostructurality across the series, and SEM‐EDS shows equal distribution of heavy atoms and similar atomic compositions across all mixed cocrystals. The acceptor molecules differ in their ability to undergo dynamic motion in the solid state. The synthetic equivalents of motion capable and incapable molecules were systematically varied to yield direct tunabililty in TE behavior.
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Abstract Control over thermal expansion (TE) behaviors in solid materials is often accomplished by modifying the molecules or intermolecular interactions within the solid. Here, we use a mixed cocrystal approach and incorporate molecules with similar chemical structures, but distinct functionalities. Development of mixed cocrystals is at a nascent stage, and here we describe the first mixed cocrystals sustained by one‐dimensional halogen bonds. Within each mixed cocrystal, the halogen‐bond donor is fixed, while the halogen‐bond acceptor site contains two molecules in a variable ratio. X‐ray diffraction demonstrates isostructurality across the series, and SEM‐EDS shows equal distribution of heavy atoms and similar atomic compositions across all mixed cocrystals. The acceptor molecules differ in their ability to undergo dynamic motion in the solid state. The synthetic equivalents of motion capable and incapable molecules were systematically varied to yield direct tunabililty in TE behavior.
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Designing materials to have three unique but predictable thermal expansion axes represents a major challenge. Inorganic materials and hybrid frameworks tend to crystallize in high-symmetry space groups, which necessarily limits this by affording isotropic behavior. On the other hand, molecular organic materials tend to crystallize in lower-symmetry space groups, offering significant opportunity to achieve anisotropic properties. The challenge arises in self-assembling the organic components into a predictable arrangement to afford predictable thermal expansion properties. Here, we demonstrate a design strategy for engineering organic solid-state materials that exhibit anisotropic thermomechanical behaviors. Presented are a series of multicomponent solids wherein one component features a BODPIY core strategically decorated with orthogonal hydrogen- and halogen-bond donor groups. A series of size-matched halogen-bond acceptors are used as the second component in each solid. By matching the molecular dimensions with the interaction strength, we obtained good control over the anisotropic thermal expansion of the molecular materials. Moreover, using shape-size mimicry and propensity for molecular motion, a rare ternary molecular system that is isostructural to the two binary solids was successfully achieved. The diiodo-functionalized BODIPY core in this study has been previously used in photocatalysts, and halogen bonding was hypothesized as a driving force; here, we provide corroborating solution and solid-state evidence of intermolecular halogen bonding in multicomponent solids featuring a 2,6-diiodo BODIPY.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/anie.202306198
