SPECTROPHOTOMETRIC STUDY, CRYSTAL AND MOLECULAR STRUCTURE OF THE 1:1 COMPLEX BETWEEN 1,3-DITHIOLANE-2-THIONE AND DIIODINE

Abstract

The reaction of 1,3-dithiolane-2-thione (dtt) with diiodine has been investigated by spectrophotometric methods in CHCl₃. The formation of a 1:1 charge-transfer complex between the reagents has been observed. The use of a general computer program has allowed to refine the formation constants and the extinction coefficients simultaneously in the whole 260–550 nm explored range. While the formation constant is rather lower (K_20° = 45 ± 1 mol⁻¹ dm³), the—ΔHo is comparable with those generally found in other moderately strong thione-donors. An X-ray crystal structure analysis of the title compound has shown that the crystals are triclinic, space group PI, with a = 7.675(6), b = 9.955(7), c = 6.161(6) Å, a = 90.08(2), β = 104.23(2), γ = 95.18(2)° and Z = 2. The molecular structure shows that the sulfur-thioamide atom of the ligand acts as the donor with respect to the diiodine molecule, and the S—I—I linkage is nearly linear [176.5(1)°]. The I—I bond length is 2.823(2) Å. The only significant changes in the bond lengths and angles of the ligand with the coordination are the distance of the neighboring C—C [1.44(2) Å], shorter than in the free ligand [1.49.3(4) Å] and consequently the S—C—C—S torsion angle [-14(2)°, -43.8(3)° in the free ligand].

Key Words:

• Charge-transfer
• diiodine
• formation constants
• X-ray
• cyclic-thioketones