The Mechanism of Bending in Co-Crystals of Caffeine and 4-Chloro-3-Nitrobenzoic Acid

Abstract

<p>In a recent study, Dey <i>et al.</i><sup>1</sup> propose a mechanism of elastic bending in co-crystals of caffeine, 4-chloro-3-nitrobenzoic acid and methanol (<b>1</b>) in which mechanical interlocking is proposed to allow for the reversible flexibility observed. We have now determined the mechanism to atomic resolution using micro-focused synchrotron radiation,<sup>2</sup> which is different to that previously reported. When subjected to strain the inter-molecular distances change and hydrogen-bonded dimers rotate over two orthogonal directions to allow the compression and expansion producing flexibility. </p>