The X-ray crystal structures of Form I and II were solved in triclinic space group . The amide group forms a dimer through N1—H1B⋯O1 [2.00 (4) Å, ∠172 (3)°] hydrogen bonds in a ring motif (Etter et al., 1990 ▸; Bernstein et al., 1995 ▸) in Form I (Fig. 3 ▸). An intramolecular hydrogen bond between the hydroxyl donor and imine nitrogen through the O2—H2A⋯N2 [1.66 (4) Å, ∠149 (4)°] ring makes an motif. The dihedral angle between the two phenyl rings is 20.07 (2)° (Table 1 ▸). The amide dimers extend through C—Cl⋯O [2.961 (3) Å] and N1—H1A⋯O2 [2.25 (4) Å, ∠161 (3)°] interactions in an eight-membered ring motif. The molecular layers are parallel to the crystallographic (1 −1 −2) plane at a distance of 3.4 Å between the molecular layers (Fig. 3 ▸). The crystal structure of Form II (Fig. 4 ▸) has the same amide dimer synthon [N1—H1B⋯O3; 2.06 (1) Å, ∠170 (1)° and N3—H3B⋯O1; 2.06 (3) Å, ∠170.4 (1)°] and N—H⋯O [N3—H3A⋯O2, 2.41 (2) Å, ∠144.3 (2)°; and N1—H1A⋯O4, 2.32 (4) Å, ∠157.4 (1)°] hydrogen bonds as in Form I. The number of symmetry independent molecules is different (Z′ = 1 in Form I and 2 in Form II). The dihedral angles between phenyl ring planes are 11.99 (17)° and 26.52 (17)°. The C—Cl⋯O interactions are 2.983 (2), 3.237 (2) Å. The chain grows parallel to the c-axis and the molecules are arranged in a wavy (corrugated) motif. Form III and IV also crystallized in the space group and with two molecules in the asymmetric unit. Forms III and IV (Figs. 5 ▸ and 6 ▸) have the same type of amide dimers which are described for the above two structures [N1—H1B⋯O3: 2.02 (2) Å, ∠170.7 (3)°; N3—H3B⋯O1: 2.17 (3) Å, ∠160.9 (1)°] and [N1—H1B⋯O3: 2.18 (2) Å, ∠161.2 (2)°; N3—H3A⋯O1: 2.04 Å, ∠170.8 (2)°], which extend via C—Cl⋯O interactions [3.04 (4), Fig. 5 ▸ a; and 3.101 (3) Å, Fig. 6 ▸ a]. The dihedral angle between two phenyl rings of the same molecule in Form III is 13.87 (4) and 23.91 (4)° and in Form IV is 12.72 (2) and 23.49 (2)°, respectively (Table 1 ▸). In Form III the amide dimers are connected by Cl⋯Cl interactions of Type I (Mukherjee et al., 2014 ▸; Desiraju & Parthasarathy, 1989 ▸) [C—Cl⋯Cl–C, 3.466 (2) Å, ∠138.4 (2)°] to form a tetrameric ring motif (Fig. S2). The planar molecular layers are parallel to the crystallographic (101) plane in Form III (Fig. 5 ▸ c). The hydrogen-bond synthons in Forms I, II, III and IV are identical except that the Cl⋯O distances vary in the polymorphs (Table 2 ▸), but these slight differences in halogen-bond distances have a dramatic consequence on the thermal response of compound A crystals (for additional diagrams of Cl⋯Cl interactions and packing in Compound A polymorphs, see Figs. S2–S3), as described in the next section. The crystal structures and hydrogen-bonding interactions for compounds B and C are discussed in the supporting information (Figs. S4–S7 and Table S3).