RETRACTED ARTICLE: Mechanically interlocked architecture aids an ultra-stiff and ultra-hard elastically bendable cocrystal

Somnath Dey,Ramesh Devarapalli,C Malla Reddy,Taro Moriwaki,Biswajit Bhattacharya,Rituparno Chowdhury,Surojit Bhunia,Nobuhiro Yasuda,Amit Mondal,Goutam Dev Mukherjee,Kapil Mandal,Susobhan Das

doi:10.1038/s41467-019-11657-0

Abstract

Molecular crystals are not known to be as stiff as metals, composites and ceramics. Here we report an exceptional mechanical stiffness and high hardness in a known elastically bendable organic cocrystal [caffeine (CAF), 4-chloro-3-nitrobenzoic acid (CNB) and methanol (1:1:1)] which is comparable to certain low-density metals. Spatially resolved atomic level studies reveal that the mechanically interlocked weak hydrogen bond networks which are separated by dispersive interactions give rise to these mechanical properties. Upon bending, the crystals significantly conserve the overall energy by efficient redistribution of stress while perturbations in hydrogen bonds are compensated by strengthened π-stacking. Furthermore we report a remarkable stiffening and hardening in the elastically bent crystal. Hence, mechanically interlocked architectures provide an unexplored route to reach new mechanical limits and adaptability in organic crystals. This proof of concept inspires the design of light-weight, stiff crystalline organics with potential to rival certain inorganics, which currently seem inconceivable.

Highlights

Mstieffchaanndicualtllrya-inhtaerrdloeclkaesdticaarlclyhibteecntduareblaeidcsocarnyLsutlatErla- Somnath Dey 1, Susobhan Das 1, Surojit Bhunia 1,2, Rituparno Chowdhury 1, Amit Mondal 1, C Biswajit Bhattacharya 1, Ramesh Devarapalli[1], Nobuhiro Yasuda 3, Taro Moriwaki 3, Kapil Mandal 4, I Goutam Dev Mukherjee 4 & C
D significantly conserve the overall energy by efficient redistribution of stress while perturbations in hydrogen bonds are compensated by strengthened π-stacking
Measured elastic modulus (E) for (010) was found to be as high as 76.86 (±1.30) GPa while for (001) face was 64.39 (±1.96) GPa (Table 1). These exceptionally high values are comparable to certain metals, such as aluminum, which has density nearly double to that of the cocrystal (1.48 gcm−3). These E values are almost nine-fold and five-fold larger than that obtained on single crystals of pure CAF (8.73 GPa)[42] and chloro-3-nitrobenzoic acid (CNB) (14–16 GPa), respectively (Supplementary Table 1 and Supplementary Fig. 6)

Summary

Introduction

Mstieffchaanndicualtllrya-inhtaerrdloeclkaesdticaarlclyhibteecntduareblaeidcsocarnyLsutlatErla- Somnath Dey 1, Susobhan Das 1, Surojit Bhunia 1,2, Rituparno Chowdhury 1, Amit Mondal 1, C Biswajit Bhattacharya 1, Ramesh Devarapalli[1], Nobuhiro Yasuda 3, Taro Moriwaki 3, Kapil Mandal 4, I Goutam Dev Mukherjee 4 & C. D Fig. 1 Mechanical properties of ambient and bent crystals obtained by nanoindentation.

Results

Conclusion