Crystal structures and Hirshfeld surface analyses of ( E )-1-[1-(4- tert -butyl-phen-yl)-2,2-di-chloro-ethen-yl]-2-phenyl-diazene, ( E )-1-[1-(4- tert -butyl-phen-yl)-2,2-di-chloro-ethen-yl]-2-(4-methyl-phen-yl)diazene, ( E )-1-[1-(4- tert -butyl-phen-yl)-2,2-di-chloro-ethen-yl]-2-(4-meth-oxy-phen-yl)diazene and ( E )-1-[1-(4- tert -butyl-phen-yl)-2,2-di-chloro-ethen-yl]-2-(3-methyl-phen-yl)diazene.

The crystal structures and Hirshfeld surface analyses of four similar azo compounds are reported. ( E )-1-[1-(4- tert -Butyl-phen-yl)-2,2-di-chloro-ethen-yl]-2-phenyl-diazene, C 18 H 18 Cl 2 N 2 , ( I ), and ( E )-1-[1-(4- tert -butyl-phen-yl)-2,2-di-chloro-ethen-yl]-2-(4-methyl-phen-yl)diazene, C 19 H 20 Cl 2 N 2 , ( II ), crystallize in the monoclinic space group C 2/ c with Z = 8, and ( E )-1-[1-(4- tert -butyl-phen-yl)-2,2-di-chloro-ethen-yl]-2-(4-meth-oxy-phen-yl)diazene, C 19 H 20 Cl 2 N 2 O, ( III ), in the monoclinic space group P 2 1 / c with Z = 4. ( E )-1-[1-(4- tert -Butyl-phen-yl)-2,2-di-chloro-ethen-yl]-2-(3-methyl-phen-yl)diazene, C 19 H 20 Cl 2 N 2 , ( IV ), crystallizes in the triclinic space group P with Z = 4 and comprises two mol-ecules ( A and B ) in the asymmetric unit. In the crystal structures of ( I ) and ( II ), mol-ecules are linked by C-H⋯π and C-Cl⋯π inter-actions, forming layers parallel to (02), while mol-ecules of ( III ) are linked by C-H⋯O contacts, C-H⋯π and C-Cl⋯π inter-actions forming layers parallel to (02). The stability of the mol-ecular packing is ensured by van der Waals forces between these layers. In the crystal structure of ( IV ), mol-ecules are linked by C-H⋯π and C-Cl⋯π inter-actions, forming a tri-periodic network.