Hirshfeld surface (Poulsen et al., 2009 ▸) analysis of polymorphs of compound A (Fig. 7 ▸) showed that Form II has a greater contribution from O⋯H and Cl⋯O contacts (14.8 and 2.6%) compared with Form I (12.9 and 2.1%), Form III (11.8 and 1.5%) and Form IV (12.1 and 1.8%, Fig. S22) indicating the stability of Form II compared with the other two forms, which was also supported in competitive slurry experiments.