Structural and spectroscopic studies of charge-transfer adducts formed between IBr and thioether crowns

Abstract

Charge-transfer complexes [9]aneS₃·2IBr ([9]aneS₃ = 1,4,7-trithiacyclononane), [14]aneS₄·2IBr 1 ([14]aneS₄ = 1,4,8,11-tetrathiacyclotetradecane), [16]aneS₄·4IBr 2 ([16]aneS₄ = 1,5,9,13-tetrathiacyclohexadecane) and [18]aneS₆·2IBr 3 ([18]aneS₆ = 1,4,7,10,13,16-hexathiacyclooctadecane) have been synthesized and the single crystal structures of 1, 2 and 3 determined. The reactions of IBr with [12]aneS₄ (1,4,7,10-tetrathiacyclododecane), [15]aneS₅ (1,4,7,10,13-pentathiacyclopentadecane) and [24]aneS₈ (1,4,7,10,13,16,19,22-octathiacyclotetracosane) have also been examined. All the compounds were prepared by slow evaporation of solutions containing IBr and the appropriate thioether macrocycle in CH₂Cl₂–n-hexane. The structure determination of 1 shows the thioether crown lying across a crystallographic inversion centre with two symmetry-related IBr molecules co-ordinated through their iodine atoms to two exo-oriented S-donors [S(1)–I(1) 2.678(1), I(1)–Br(1) 2.654(2) Å, S(1)–I(1)–Br(1) 175.53(4)°]. The Br· · ·Br contacts between consecutive adduct units form polymeric chains of 1 in the crystal lattice. Compound 2 is the only adduct in the present investigation to have all S-donor atoms of the macrocyclic ligand co-ordinated to IBr molecules [S(1)–I(1) 2.618(2), I(1)–Br(1) 2.7049(11), S(5)–I(5) 2.687(2), I(5)–Br(5) 2.6445(12) Å, S(1)–I(1)–Br(1) 177.65(5), S(5)–I(5)–Br(5) 177.57(5)°]. The [16]aneS₄·4IBr units interact with each other through I· · ·I and Br· · ·I contacts to form ribbons of interconnected molecules of 2 which propagate along the ab face diagonals of the unit cell. Compound 3 shows two symmetry-related IBr molecules co-ordinated to the macrocyclic ligand [S(1)–I(1) 2.619(3), I(1)–Br(1) 2.695(2) Å, S(1)–I(1)–Br(1) 175.00(6)°]. Adduct molecules are stacked along the b axis and held together by S· · ·S interactions between [18]aneS₆ units. The structural features and the FT-Raman spectra of the reported IBr adducts are compared with those of the I₂ adducts obtained from the same ligands.