Isostructural polymorphs of triiodophloroglucinol and triiodoresorcinol

Triiodoresorcinol (TIR, 2,4,6-triiodoresorcinol) and triiodophloroglucinol (TIG, 2,4,6-triiodophloroglucinol) crystallized as orthorhombic (TIR-O and TIG-O in P212121) and monoclinic (TIR-M and TIG-M in P21/n) polymorphs mediated via inter-halogen I⋯I interactions. The orthorhombic polymorphs are isostructural and in turn similar to the crystal structure of 1,3,5-triiodobenzene (TIB). The isostructural monoclinic polymorphs are similar to the structure of 1,3,5-trifluoro-2,4,6-triiodobenzene (TIF). Triiodophenol (TIP) crystallized in a single orthorhombic form only. The monoclinic structures have tandem O–H⋯O hydrogen bonds in addition to inter-iodine interactions. The similarity of crystal structures was confirmed by the formation of 1 : 1 binary solid-solutions, TIP + TIR-O and TIR + TIG-O, in orthorhombic space groupP212121. Dimorphs of TIR and TIG establish a structural link in the triiodobenzene series TIB (P212121) → TIP (P212121) → TIR (P212121 and P21/n) → TIG (P212121 and P21/n) → TIF (P21/n). The search for new polymorphs was initiated by isostructurality relationship in the series of compounds.