Atomic resolution of structural changes in elastic crystals of copper(II) acetylacetonate


Single crystals are typically brittle, inelastic materials. Such mechanical responses limit their use in practical applications, particularly in flexible electronics and optical devices. Here we describe single crystals of a well-known coordination compound—copper(II) acetylacetonate—that are flexible enough to be reversibly tied into a knot. Mechanical measurements indicate that the crystals exhibit an elasticity similar to that of soft materials such as nylon, and thus display properties normally associated with both hard and soft matter. Using microfocused synchrotron radiation, we mapped the changes in crystal structure that occur on bending, and determined the mechanism that allows this flexibility with atomic precision. We show that, under strain, the molecules in the crystal reversibly rotate, and thus reorganize to allow the mechanical compression and expansion required for elasticity and still maintain the integrity of the crystal structure.

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Figure 1: Crystal structure of [Cu(acac)2].
Figure 2: Mechanical properties of single crystals of [Cu(acac)2].
Figure 3: Structure changes in [Cu(acac)2] crystals during flexure.


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We thank the Australian Research Council for support. Part of this research was undertaken on the MX1 and MX2 beamlines of the Australian Synchrotron, Clayton, Victoria, Australia. We thank Australian Synchrotron for travel support and their staff for assistance. We thank the University of Queensland, Queensland University of Technology and the Central Analytical Research Facility (CARF, QUT) for support.

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A.W., M.C.P. and A.G. synthesized the materials investigated. A.G., A.W., M.C.P., J.K.C. and J.C.M. performed the X-ray measurements. A.W., A.G., M.C.P., Y.X., C.Y. and G.E. performed the mechanical measurements. J.K.C. and J.C.M. conceptualized the studies and directed the research. A.W., A.G., M.C.P., J.K.C. and J.C.M. wrote the manuscript.

Corresponding authors

Correspondence to Jack K. Clegg or John C. McMurtrie.

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The authors declare no competing financial interests.

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Supplementary Movie 1 (MP4 35949 kb)

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Supplementary Movie 1 (MP4 35949 kb)


Supplementary Movie 2 (MP4 6669 kb)

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Supplementary Movie 2 (MP4 6669 kb)

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Crystallographic data for the unbent [Cu(acac)2] (CIF 299 kb)

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Crystallographic data for Crystal 1 (structures a to p) (CIF 355 kb)

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Crystallographic data for Crystal 2 (structures a to r) (CIF 420 kb)

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Worthy, A., Grosjean, A., Pfrunder, M. et al. Atomic resolution of structural changes in elastic crystals of copper(II) acetylacetonate. Nature Chem 10, 65–69 (2018).

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