Thioether-iodine charge-transfer complexes. Synthesis and low temperature single-crystal structures of complexes of penta-, hexa- and octa-dentate homoleptic thioether macrocycles

Charge-transfer complexes 2([15]aneS(5),).7I(2), I ([15]aneS(5), = 1,4,7,10, 13-pentathiacyclopentadecane), [18]aneS(6).I-2 2, [18]aneS(6).4I(2)3 ([18]aneS(6) = 1,4,7,10,13,16-hexathiacyclooctadecane) [24]aneS(8).I(2)4 and [24]aneS(8).6I(2)5 ([24]aneS(8) = 1,4,7,10,13,16,19,22-octathiacyclotetracosane) have been prepared and their structures and solution properties investigated. The compounds were prepared by slow evaporation of solutions containing I-2 and the appropriate thioether macrocycle in CH2CI2. The single-crystal structure determination of I shows three I, molecules coordinated to three exo oriented S donors [S(I)-I(I) 2.797(3), I(1)-I(1') 2.798(2), S(4)-I(4) 2.885(4), 1(4)-I(4') 2.764(2), S(7)-I(7) 2.828(3) and 1(7)-I(7') 2.779(2) Angstrom; S(I)-I(I)-I(1') 178.39(8), S(4)-I(4)-I(4') 171.12(8), S(7)-I(7)-I(7') 178.80(8)degrees]. The fourth I,molecule (with a site occupancy of 0.5) lies close to S(IO) [I(IO)-S(10) 2.839(5) Angstrom], the bond distance 1(10)-I(10') 2.674(3) Angstrom being unusually short. Compound 2 is an example of a 1:1 I-2,:macrocycle adduct and shows symmetrically bridging I-2 molecules [S(I)-I(I) 3.099(2), I(1)-I(1') 2.7881(10) Angstrom; 8(1)-I(1)-I(1') 178.68(4)degrees; i I - x, 1 - y, 1 - z] between [18]aneS(6), macrocycles. Compound 3 is the first example of an adduct between I-2, and a homoleptic thioether macrocycle which shows both exo [S(I)-I(I) 2.838(2), I(1)-I(1') 2.7875(6) Angstrom; S(1)-I(1)-I(1') 174.95(4)degrees] and endo [S(4)-I(4) 2.792(2), I(4)-I(4') 2.8067(7) Angstrom S(4)-I(4)-I(4') 174.43(4)degrees] co-ordination of I-2, molecules. The endo-oriented I-2, molecules occupy space above and below the macrocyclic plane with the macrocycle adopting a sigmoid conformation. The single-crystal structure determination of the I : 1 adduct 4 shows symmetrically bridging I-2 molecules [8(1)-I(1) 3.215(2) and I(1)-I(1') 2.758(2) Angstrom; S(1)-I(1)-I(IL) 172.75(3)degrees; i -x, -y, -z] which are a characteristic of this stoichiometry. Compound 5 contains endo- and exo-oriented S donors within the same adduct [1(1)-I(1') 2.7861(8), 1(4)-I(4') 2.7937(8), 1(7)-I(7') 2.8345(8), S(I)-I(I) 2.821(2), S(4)-I(4) 2.815(2), S(7)-I(7) 2.741(2) Angstrom; S(I)-I(I)-I(1') 170. i 5(5), 8(4)-I(4)-I(4') 177.41(5), S(7)-I(7)-I(7') 177.24(5)degrees]. These results are discussed in the context of the stability and characteristics of thioether crown-iodine charge-transfer complexes, and a qualitative MO diagram is proposed to account for the shorter I-I distances in bridging I-2 fragments compared to those in terminally bound I-2.