Supramolecular-jack-like guest in ultramicroporous crystal for exceptional thermal expansion behaviour.

Hao-Long Zhou,Jie-Peng Zhang,Xiao-Ming Chen,Yue-Biao Zhang

doi:10.1038/ncomms7917

Hao-Long Zhou, Jie-Peng Zhang + Show 2 more

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https://doi.org/10.1038/ncomms7917

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Abstract

The dynamic behaviours of host frameworks and guest molecules have received much attention for their great relevance with smart materials, but little has been developed to control or understand the host–guest interplay. Here we show that the confined guest can utilize not only molecular static effects but also bulk dynamic properties to control the host dynamics. By virtue of the three-dimensional hinge-like framework and quasi-discrete ultramicropores, a flexible porous coordination polymer exhibits not only drastic guest-modulation effect of the thermal expansion magnitude (up to 422 × 10−6 K−1) and even the anisotropy but also records positive/negative thermal expansion coefficients of +482/−218 × 10−6 K−1. Moreover, single-crystal X-ray diffraction analyses demonstrate that the jack-like motion of the guest supramolecular dimers, being analogous to the anisotropic thermal expansion of bulk van der Waals solids, is crucial for changing the flexibility mode and thermal expansion behaviour of the crystal.

Highlights

The dynamic behaviours of host frameworks and guest molecules have received much attention for their great relevance with smart materials, but little has been developed to control or understand the host–guest interplay
Flexible porous coordination polymers (PCPs) are emerging as an ideal platform for realizing abnormal temperature-induced structural dynamic behaviours, such as negative thermal expansion (NTE)[11,12,13,14] and very large thermal expansion, which have great potential for compensation of the small positive thermal expansion (PTE, 0oao[20] Â 10À6 KÀ1) of common solids, designing sensitive thermomechanical actuators, and so on[21,22,23,24,25,26,27,28,29]
As the most remarkable examples, Kepert and coworkers achieved isotropic PTE (a 1⁄4 þ10.0 Â 10À6 KÀ1) to NTE (a 1⁄4 À33.5 Â 10À6 KÀ1) transition via guest removal in [Cd(CN)2]ÁxCCl441, and Barbour and coworkers showed that the PTE of [Zn(OH)(niba)]Áalcohol (Hniba 1⁄4 4-(1Hnaphtho[2,3-d]imidazol-1-yl)benzoic acid) can be increased by B90 Â 10À6 KÀ1 via changing the alcohol guest molecules[18], in which the microporous structures have been demonstrated to be crucial for realizing the guest-modulation effect, since they maximize host–guest interaction around the guest molecules[17,18,40,41]

Summary

Introduction

The dynamic behaviours of host frameworks and guest molecules have received much attention for their great relevance with smart materials, but little has been developed to control or understand the host–guest interplay. By virtue of the three-dimensional hinge-like framework and quasi-discrete ultramicropores, a flexible porous coordination polymer exhibits drastic guestmodulation effect of the thermal expansion magnitude (up to 422 Â 10À6 KÀ1) and even the anisotropy and records positive/negative thermal expansion coefficients of þ482/À218 Â 10À6 KÀ1. To enable direct observation of thermal expansion of guest aggregations, discrete, isolated or 0D pores with suitable sizes for accommodation of two or a little bit more guest molecules should be optimal[46,47]. Materials with such pores are generally difficult to change guests, preventing rational modulation of the physical property[20,48,49]. We report a drastic guest-modulation effect, and even a change of the main thermal expansion direction since the steric hindrance and thermal expansion effects of the guest dimers are large enough to alter the flexibility mode of the host framework (Fig. 1)

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