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

The charge-transfer complexes 2[9]aneS(3) . 4I(2)([9]aneS(3) = 1,4,7-trithiacyciononane), [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 CH2Cl2. 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, 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) Angstrom. The adduct [14]aneS(4) . 2I(2) shows two independent macrocycles each coordinated to two I, 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) Angstrom. The formation enthalpies (Delta H) and constants (K) of 1 : 1 adducts obtained by treating various thioether macrocycles with I-2 in CH2Cl2 have been determined by electronic spectroscopy. The Fourier-transform Raman spectra for all the charge-transfer adducts have been recorded in CH2Cl2 solutions at different concentrations. The Raman frequencies of the V(I-I) vibrations show good correlation with the measured formation enthalpies Delta H.