Compound A showed a mechanical response towards heating but not the Br and I derivatives, even though these structures have the same type of hydrogen bonds and halogen bonding synthons and are three-dimensional isostructural (Xpac analysis; Figs. S18–20). The most probable reason for mechanical response is mainly due to a change in the halogen atom and also the halogen-bond interactions (Table S3). The interaction energy for the C—X⋯O (X = F, Cl, Br and I) bond increases with an increase in polarizability and a decrease of electronegativity for the halogen atom (Politzer et al., 2010 ▸; Riley & Hobza, 2008 ▸; Riley & Merz, 2007 ▸). The combined effects of both factors increases the σ hole for halogens towards a more +ve lobe in the order of I > Br > Cl. The increased electrostatic interaction between the σ hole of the halogen and oxygen lone pair electrons results in strengthening of the halogen bond from C—Cl⋯O through C—Br⋯O to C—I⋯O (Table 3 ▸) (Riley & Merz, 2007 ▸). In effect, the stronger halogen-bonded structures (having near-identical amide N—H⋯O hydrogen bonds) with Br and I atoms make them less responsive to temperature and mechanical stress because the halogen bond is too strong for the heavier halogens to show structural (and property) dynamics, indicating the importance of weaker C—Cl⋯O interactions in exhibiting the mechanical response of molecular crystals and temperature effects.