Isostructural polymorphs of triiodophloroglucinol and triiodoresorcinol

Abstract

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.