A unique case of polymorphism in polyiodide networks resulting from the reaction of the drug methimazole and I2

Abstract

The oxidation of thioamide methimazole (C₄H₆N₂S) with molecular diiodine in water afforded the ionic compound [2(C₄H₅N₂S–SN₂C₄H₆)]I₃I₅ (1) in 1-triclinic and 1-monoclinic polymorphs. The polymorphic nature of [C₄H₅N₂S–SN₂C₄H₆]₂I₃I₅ has been highlighted by comparing the structure of the 1-triclinic form with that of the 1-monoclinic form reported in the literature. No significant geometric differences are observed for the cations in the two polymorphs. The polymorphism is essentially due to a different arrangement in the polyiodide network of the [I₅]⁻ and [I₃]⁻ components. The FT-Raman spectrum of 1-triclinic shows the characteristic bands in the range 200–50 cm⁻¹ which are in good agreement with the structural features of the polyiodide network. The molecular electrostatic potential maps of the cation methimazole-disulfide [C₄H₅N₂S–SN₂C₄H₆]⁺ and the bis-cation methimazole-disulfide {[C₄H₅N₂S–SN₂C₄H₆]⁺}₂ in 1-triclinic have been studied to clearly identify the electrostatic potential energy distributions over the cations, and the electron belt and σ-hole areas responsible for the directionality of the non-covalent interactions in the polyiodides. It is suggested that the cation methimazole-disulfide may be a reaction intermediate in the inhibition of thyroid hormones by methimazole.