Extraordinary anisotropic thermal expansion in photosalient crystals.

Khushboo Yadava,Raghavender Medishetty,Caroline Evania Mulijanto,Panče Naumov,Jagadese J Vittal,Durga Prasad Karothu,In-Hyeok Park,Sebastian Bette,Gianpiero Gallo,Robert E Dinnebier

doi:10.1107/s2052252519014581

Abstract

Although a plethora of metal complexes have been characterized, those having multifunctional properties are very rare. This article reports three isotypical complexes, namely [Cu(benzoate)L 2], where L = 4-styryl-pyridine (4spy) (1), 2'-fluoro-4-styryl-pyridine (2F-4spy) (2) and 3'-fluoro-4-styryl-pyridine (3F-4spy) (3), which show photosalient behavior (photoinduced crystal mobility) while they undergo [2+2] cyclo-addition. These crystals also exhibit anisotropic thermal expansion when heated from room temperature to 200°C. The overall thermal expansion of the crystals is impressive, with the largest volumetric thermal expansion coefficients for 1, 2 and 3 of 241.8, 233.1 and 285.7 × 10-6 K-1, respectively, values that are comparable to only a handful of other reported materials known to undergo colossal thermal expansion. As a result of the expansion, their single crystals occasionally move by rolling. Altogether, these materials exhibit unusual and hitherto untapped solid-state properties.

Highlights

Multifunctional smart materials can perform multiple functions through tailored chiral, electronic, magnetic, optical, thermal and/or mechanical properties that can be used for energy storage and conversion, drug delivery, catalysis, etc
Multiferroic properties have been accomplished with MOFs and metal complexes (Wu et al, 2010; Ramesh & Spaldin, 2007; Spaldin et al, 2005; Cheong & Mostovoy, 2007)
We report that the crystals of [Cu2(benzoate)4(L)2], where L = 4-styrylpyridine (4spy) (1), 20-fluoro-4-styrylpyridine (2F-4spy) (2) and 30-fluoro-4-styrylpyridine (3F-4spy) (3) pop violently under UV light, and they are photosalient. Crystals of these materials exhibit very large anisotropic thermal expansion when heated from room temperature to about 200C

Summary

Introduction

Multifunctional smart materials can perform multiple functions through tailored chiral, electronic, magnetic, optical, thermal and/or mechanical properties that can be used for energy storage and conversion, drug delivery, catalysis, etc. These photodynamic and thermodynamic crystals set new avenues for materials that can be used to convert light or heat into mechanical work. A smart hybrid material was prepared by incorporating this complex into thin films of sodium caseinate which exhibits dual mechanical response (to heat and light), showing potential for preparation of hybrid materials by using salient crystals (Sahoo et al, 2014) In another example, a cocrystal of probenecid and 4,40-azopyridine was shown to be thermally twistable, photobendable, elastically deformable and selfhealable, and this material can be considered a multifunctional, smart, soft crystalline solid (Gupta et al, 2018). Crystals of these materials exhibit very large anisotropic thermal expansion when heated from room temperature to about 200C

Results and discussion

Conclusions

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