A new assembly of diiodine molecules at the 1,3-dimethylimidazole-2-thione (Me2ImS) template: crystal structure of (Me2ImS)2·(I2)5

Abstract

The new poly(I₂) adduct [(Me₂ImS)₂·(I₂)₅] (Me₂ImS = 1,3-dimethylimidazole-2-thione) has been synthesized and characterized by single crystal X-ray diffraction analysis. Units of [(Me₂ImS)₂·(I₂)₅] are located about a crystallographic inversion center, in which five diiodine molecules display interatomic contacts in a “head-to-tail” sequence giving a –(I₂)₅– chain interacting at each end with one Me₂ImS molecule, CCDC 2133501. The S-bonding of Me₂ImS to I₂ is described as a donor–acceptor interaction in which I₂ acts as an acceptor through the σ*(I–I) orbital resulting in an electronic charge transfer from the thioamide moiety. The bond distances d(S–I(1)) (2.504(2) Å) and d(I(1)–I(2)) (3.133(1) Å) are indicative of a strong interaction. Based on the S–I and I–I bond distances, the calculated values of the electronic charge densities, and the Raman spectral data, it is reasonable to represent the compound as an extended polarised system: [(Me₂ImS)–I(1)]^δ+⋯I(2)^δ−⋯I(3)–I(4)^δ−⋯(I(5)–I(5)^a)⋯I^δ−–I⋯I^δ−⋯[I-(Me₂ImS)]^δ+. The molecular electrostatic potential maps of the three adducts Me₂ImS·I₂, Me₂ImS·I₂·I₂, and MeImHS·I₂ (MeImHS = methimazole) have been reported to clearly identify the areas of charge increment (electron belt) and depletion (σ-hole), and thus the directionality of the noncovalent interactions.