Understanding the elastic bending mechanism in 9,10-anthraquinone crystal through thermal expansion study
Owing to the enormous potential applications in materials science and biomedical field, during the last decade the two fields, thermal expansion and flexible materials of small molecular crystals, have gained some special attention among the researchers. However, till date there is only one report from us in which these two fields have been correlated. Here we have shown that 9,10-anthraquinone crystal exhibits remarkable flexibility and then correlated thermal expansion with flexibility for this crystal. In this study we have first shown that 9,10-anthraquinone exhibits elastic bending. Then we showed that it is possible to correlate thermal expansion mechanism with the bending mechanism in the case of Cu(acac)2 crystal for which the crystal structure of the bent crystal as well as thermal expansion data are available. Then this idea has been extended to elucidate the bending mechanism in elastic bending of 9,10-anthraquinone crystal for which the crystal packing is very similar to that of Cu(acac)2 crystal. We have shown here that some of the structural features along the bending axis, the outer face and the inner face of the bent crystal would resemble to the thermally expanded and contracted crystal structures along the same side. We also have shown here that there are only three systems, including this, for which bending as well as thermal expansion studies have been performed so far. Interestingly, in all these three cases the bending axis, along which the structure has to be expanded at the outer face or contracted at the inner face, is parallel to the major principal axis of linear thermal expansion along which the crystal can easily be expanded or contracted through thermal treatment. We anticipate that thermal expansion study would be very useful to explain many bending phenomena of the single crystals of small molecules.