The vibrational spectra and structure of the Bis(hexamethylenetetramine)iodine(I) cation

Abstract

The crystalline compound reported in the literature as the 1 : 1 addition complex of hexamethylenetetramine (hx) with iodine is shown by means of i.r. and Raman spectroscopy to be an ionic compound consisting of bis(hexamethyl-enetetramine)iodine(I) ions, (hx)₂I⁺, and I₃^- ions. A crystalline compound consisting of molecules of the true 1 : 1 addition complex (hx)I₂ does exist, however, and its preparation is described. On standing, this compound undergoes an unusual solid state transformation, resulting in the formation of the ionic complex. The (hx)₂I⁺ ion is the first documented example of a bis(amine)halogen(I) ion involving an amine other than pyridine or its derivatives. A structure for this ion is proposed in which the hexamethylenetetramine molecules are bound to the iodine atom through one of their nitrogen atoms, the resulting N...I...N arrangement being linear, centrosymmetric, and lying along the threefold axis passing through the coordinated nitrogen atom of each hexamethylenetetramine molecule. The evidence for this structure obtainable from the vibrational spectra of the ion is discussed. A preliminary investigation of the valence force field indicates unusually strong nitrogen-iodine bonding in this ion. The literature method for preparing bis-(pyridine)halogen(I) perchlorates has been modified and used to prepare the perchlorate of bis(hexamethylenetetramine)iodine(I).