Structural and solution studies of diiodine charge-transfer complexes of thioether crowns

Abstract

The charge-transfer complexes 2[9]aneS ₃ ·4I ₂ ([9]aneS ₃ = 1,4,7-trithiacyclononane), [12]aneS ₄ ·I ₂ ([12]aneS ₄ = 1,4,7,10-tetrathiacyclododecane), [14]aneS ₄ ·I ₂ , [14]aneS ₄ ·2I ₂ ([14]aneS ₄ = 1,4,8,11-tetrathiacyclotetradecane), [16]aneS ₄ ·I ₂ and [16]aneS ₄ ·4I ₂ ([16]aneS ₄ = 1,5,9,13-tetrathiacyclohexadecane) have been prepared by slow evaporation of solutions containing I ₂ and the appropriate thioether macrocycle in CH ₂ Cl ₂ . The structure of 2[9]aneS ₃ ·4I ₂ shows two independent macrocycles in the asymmetric unit which are linked by a diiodine bridge. Asymmetric units are linked by I · · · I and S · · · I interactions to form an extended array of linked macrocycles. The single-crystal structure of [12]aneS ₄ ·I ₂ features an infinite chain structure formed by alternating [12]aneS ₄ and I ₂ molecules. The structure contains both symmetric and asymmetric diiodine bridges. Although the 1∶1 adduct [14]aneS ₄ ·I ₂ can also be described as a one-dimensional infinite chain structure with asymmetric diiodine bridging, the structure is better visualised as alternating layers of macrocycle and iodine spanned by short contacts of 3.335(4) Å. The adduct [14]aneS ₄ ·2I ₂ shows two independent macrocycles each co-ordinated to two I ₂ molecules. The charge-transfer network consists of chains of molecules with alternating orientations. The single-crystal structure of a third 1∶1 adduct [16]aneS ₄ ·I ₂ contains only symmetrical diiodine bridges between neighbouring macrocycles leading to an infinite chain structure. The compound [16]aneS ₄ ·4I ₂ is the first example of a tetradentate macrocycle which incorporates I ₂ bound to all four S atoms. The single-crystal structure shows four terminal I ₂ molecules co-ordinated to the four S donors of the macrocycle. Molecules are linked into interwoven sheets by I · · · I interactions of 3.639(2) Å. The formation enthalpies (ΔH) and constants (K) of 1∶1 adducts obtained by treating various thioether macrocycles with I ₂ in CH ₂ Cl ₂ have been determined by electronic spectroscopy. The Fourier-transform Raman spectra for all the charge-transfer adducts have been recorded in CH ₂ Cl ₂ solutions at different concentrations. The Raman frequencies of the ν(I–I) vibrations show good correlation with the measured formation enthalpies ΔH.