STRUCTURAL AND SOLUTION STUDIES OF DIIODINE CHARGE-TRANSFER COMPLEXESOF THIOETHER CROWNS

The charge-transfer complexes 2[9]aneS(3) . 4I(2)([9]aneS(3) = 1,4,7-t rithiacyciononane), [12]aneS(4) . I-2 ([12]aneS(4) = 1,4,7,10-tetrathi acyclododecane), [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 appro priate thioether macrocycle in CH2Cl2. The structure of 2[9]aneS(3) . 4I(2) shows two independent macrocycles in the asymmetric unit which a re linked by a diiodine bridge. Asymmetric units are linked by I ... I and S ... I interactions to form an extended array of linked macrocyc les. The single-crystal structure of [12]aneS(4) . I-2 features an inf inite chain structure formed by alternating [12]aneS(4) and I-2 molecu les. The structure contains both symmetric and asymmetric diiodine bri dges. Although the 1:1 adduct [14]aneS, I-2 can also be described as a one-dimensional infinite chain structure with asymmetric diiodine bri dging, the structure is better visualised as alternating layers of mac rocycle and iodine spanned by short contacts of 3.335(4) Angstrom. The adduct [14]aneS(4) . 2I(2) shows two independent macrocycles each coo rdinated 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 symm etrical diiodine bridges between neighbouring macrocycles leading to a n infinite chain structure. The compound [16]aneS(4) . 4I(2) is the fi rst 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. Mol ecules 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 wi th I-2 in CH2Cl2 have been determined by electronic spectroscopy. The Fourier-transform Raman spectra for all the charge-transfer adducts ha ve 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.