Interaction of morpholine and thiomorpholine with molecular diiodine:X-ray crystal structure of morpholinium triiodide

The reactions between the donors morpholine (1) and thiomorpholine (2) with I₂ in low polar solvents (C₆H₆, CHCl₃, CH₂Cl₂) and different donor/I₂ concentration ratios (1:1, 1:2, 1:3) yield solids of stoichiometry 1·I₂, 1H⁺I⁻₃, 1H⁺I⁻₅, 2·I₂, and 2H⁺I⁻₃. Crystals suitable for X-ray structure determination have been obtained only for 1 H⁺I⁻₃. All the solids were characterized by FT-Raman and FT-IR spectroscopies in the region of the v(I-I) frequencies. Studies in solution have been carried out on each of the reactions between 1, 2, and N-methylmorpholine (3) with I₂. The formation constants of their 1:1 adducts determined at 20°C by UV-visible spectroscopy are 1781, 8500, and 8400 dm³ mol⁻¹, respectively. IR spectroscopy shows that I₂ binds the nitrogen of 1 and 2 both in axial and equatorial positions. Further, FT-Raman and ¹³CNMR spectroscopies support the nature of weak adducts between 1 (2) and the molecular diiodine in solution. © 1997 John Wiley & Sons, Inc.