Spectrophotometric study of the reaction of iodine and bromine with two new macrocycle diamides and di-ortho methoxybenzoyl thiourea in chloroform solution

The complex formation reactions of iodine and bromine with two new macrocyc le diamides (1 and 2) and di-ortho methoxybenzoyl thiourea (DOMBT) (3) have been studied spectrophotometrically at various temperatures in chloroform solution. In all cases the resulting 1:2 (macrocycle to halogen) or (DOMBT to halogen) molecular complexes were formulated as (macrocycle...X+) X-3(-) or (DOMBT.... X+)X-3(-). The formation constants of the resulting molecula r complexes were evaluated from computer fitting of the absorbance-mole rat io data. For iodine complexes we found that the Values of K-f vary in the o rder of 1 approximate to 2 > 3. In the case of bromine complexes the values of K-f are larger (> 10(8)) and vary in the order of 1 > 2 > 3. The enthal py and entropy of complexation reactions of iodine with 1, 2 and 3 were det ermined from the temperature dependence of the formation constants. In all cases it was found that the complexation reactions are enthalpy stabilized, but entropy destabilized. (C) 1999 Elsevier Science B.V. All rights reserv ed.