Crystal structures and Hirshfeld surface analyses of methyl 4-{2,2-di-chloro-1-[(E)-phenyl-diazen-yl]eth-enyl}benzoate, methyl 4-{2,2-di-chloro-1-[(E)-(4-methyl-phen-yl)diazen-yl]ethen-yl}benzoate and methyl 4-{2,2-di-chloro-1-[(E)-(3,4-di-methyl-phen-yl)diazen-yl]ethen-yl}benzoate.

The crystal structures and Hirshfeld surface analyses of three similar azo compounds are reported. Methyl 4-{2,2-di-chloro-1-[(E)-phenyl-diazen-yl]ethen-yl}benzoate, C16H12Cl2N2O2, (I), and methyl 4-{2,2-di-chloro-1-[(E)-(4-methyl-phen-yl)diazen-yl]ethen-yl}benzoate, C17H14Cl2N2O2, (II), crystallize in the space group P21/c with Z = 4, and methyl 4-{2,2-di-chloro-1-[(E)-(3,4-di-methyl-phen-yl)diazen-yl]ethen-yl}benzoate, C18H16Cl2N2O2, (III), in the space group P with Z = 2. In the crystal of (I), mol-ecules are linked by C-H⋯N hydrogen bonds, forming chains with C(6) motifs parallel to the b axis. Short inter-molecular Cl⋯O contacts of 2.8421 (16) Šand weak van der Waals inter-actions between these chains stabilize the crystal structure. In (II), mol-ecules are linked by C-H⋯O hydrogen bonds and C-Cl⋯π inter-actions, forming layers parallel to (010). Weak van der Waals inter-actions between these layers consolidate the mol-ecular packing. In (III), mol-ecules are linked by C-H⋯π and C-Cl⋯π inter-actions forming chains parallel to [011]. Furthermore, these chains are connected by C-Cl⋯π inter-actions parallel to the a axis, forming (01) layers. The stability of the mol-ecular packing is ensured by van der Waals forces between these layers.