Spatially resolved analysis of short-range structure perturbations in a plastically bent molecular crystal

• Published in: Nature chemistry Vol. 7; no. 1; pp. 65 - 72
• Main Authors: Panda, Manas K., Ghosh, Soumyajit, Yasuda, Nobuhiro, Moriwaki, Taro, Mukherjee, Goutam Dev, Reddy, C. Malla, Naumov, Panče
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2015; Nature Publishing Group
• Subjects: 140/133; 147/135; 147/3; 639/638/298/303; Analytical Chemistry; Biochemistry; Chemistry; Chemistry/Food Science; Crystals; Deformation; Hexachlorobenzene; Inorganic Chemistry; Organic Chemistry; Physical Chemistry; Science education; Single crystals; Abu Dhabi United Arab Emirates; United Arab Emirates; India
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/nchem.2123

The exceptional mechanical flexibility observed with certain organic crystals defies the common perception of single crystals as brittle objects. Here, we describe the morphostructural consequences of plastic deformation in crystals of hexachlorobenzene that can be bent mechanically at multiple locations to 360° with retention of macroscopic integrity. This extraordinary plasticity proceeds by segregation of the bent section into flexible layers that slide on top of each other, thereby generating domains with slightly different lattice orientations. Microscopic, spectroscopic and diffraction analyses of the bent crystal showed that the preservation of crystal integrity when stress is applied on the (001) face requires sliding of layers by breaking and re-formation of halogen–halogen interactions. Application of stress on the (100) face, in the direction where π ··· π interactions dominate the packing, leads to immediate crystal disintegration. Within a broader perspective, this study highlights the yet unrecognized extraordinary malleability of molecular crystals with strongly anisotropic supramolecular interactions. Crystals of hexachlorobenzene easily break when pressed on the (100) face, but bend to 360° without disintegrating when stress is applied on the (001) face. In the latter case this extraordinary malleability arises from the segregation and sliding of layers of molecules in the crystal, a process in which halogen–halogen interactions are broken and reformed.