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The mol­ecular and crystal structures of two isomeric bis­(iodo­meth­yl)benzene derivatives are reported. A comparison is made of the inter­molecular contacts stabilizing the packing in the two closely related systems., The isomeric derivatives 1,2-bis­(iodo­meth­yl)benzene, (I), and 1,3-bis­(iodo­meth­yl)benzene (II), both C8H8I2, were prepared by metathesis from their di­bromo analogues. The ortho-derivative, (I), lies about a crystallographic twofold axis that bis­ects the C—C bond between the two iodo­methyl substituents. The packing in (I) relies solely on C—H⋯I hydrogen bonds supported by weak parallel slipped π–π stacking inter­actions [inter-centroid distance = 4.0569 (11) Å, inter-planar distance = 3.3789 (8) Å and slippage = 2.245 Å]. While C—H⋯I hydrogen bonds are also found in the packing of (II), type II, I⋯I halogen bonds [I⋯I = 3.8662 (2) Å] and C—H⋯π contacts feature prominently in stabilizing the three-dimensional structure.

In the cation of the title salt, C18H20N3+·I−, the mesityl and phenyl rings are inclined to the central triazolium ring by 61.39 (16) and 30.99 (16)°, respectively, and to one another by 37.75 (15)°. In the crystal, molecules are linkedviaC—H...I hydrogen bonds, forming slabs parallel to theabplane. Within the slabs there are weak π–π interactions present involving the mesityl and phenyl rings [inter-centroid distances are 3.8663 (18) and 3.8141 (18) Å].