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

Charge-transfer complexes [9]aneS(3). 2IBr ([9]aneS(3) = 1,4,7-trithiacyclononane), [14]aneS(4). 2IBr 1 ([14]aneS(4) = 1,4,8,11-tetrathiacyclotetradecane), [16]aneS(4). 4IBr 2 ([16]aneS(4) = 1,5,9,13-tetrathiacyclohexadecane) and [18]aneS(6). 2IBr 3 ([18]aneS(6) = 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]aneS(4) (1,4,7,10-tetrathiacyclododecane), [15]aneS(5) (1,4,7,10,13-pentathiacyclopentadecane) and [24]aneS(8) (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 eso-oriented S-donors [S(1)-I(1) 2.678(1), I(1)-Br(1) 2.654(2) Angstrom, S(1)-I(1)-Br(1) 175.53(4)degrees]. 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) Angstrom, S(1)-I(1)-Br(1) 177.65(5), S(5)-I(5)-Br(5) 177.57(5)degrees]. The [16]aneS(4). 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) Angstrom, S(1)-I(1)-Br(1) 175.00(6)degrees]. Adduct molecules are stacked along the b axis and held together by S ... S interactions between [18]aneS(6) units. The structural features and the FT-Raman spectra of the reported IBr adducts are compared with those of the I-2 adducts obtained from the same ligands.