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, C 16 H 12 Cl 2 N 2 O 2 , ( I ), and methyl 4-{2,2-di-chloro-1-[( E )-(4-methyl-phen-yl)diazen-yl]ethen-yl}benzoate, C 17 H 14 Cl 2 N 2 O 2 , ( II ), crystallize in the space group P 2 1 / c with Z = 4, and methyl 4-{2,2-di-chloro-1-[( E )-(3,4-di-methyl-phen-yl)diazen-yl]ethen-yl}benzoate, C 18 H 16 Cl 2 N 2 O 2 , ( 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) Å and 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.