Two iodine-rich (dimethylphosphoryl)methanaminium iodides

Abstract

Abstract The reaction of dpma (dpma=(dimethylphosphoryl)methanamine) with hydroiodic acid in the presence of an excess of elemental iodine gives red coloured crystals of (dpmaH)3(H3O)I4·1/2I2 (1) as the main product and a small amount of a by-product (dpmaH)2[I3]2·dpma (2). Single crystal structure determinations on both compounds were carried out. In the crystal structure of 1 (space group P3̅, a=12.2166(3) Å, c=10.8788(4) Å, R gt(F)= 0.0224, wR ref(F 2)=0.0377), six symmetry related dpmaH+ cations and iodide anions, both located in general positions, form a cage through NH···I hydrogen bonds. These cages are connected to neighbouring ones by H3O+ cations by means of strong OH···O hydrogen bonds, thereby constructing a 2-dimensional network perpendicular to the c direction. In the center of each cage a three-fold disordered I2 molecule is present. This disorder is a consequence of space group symmetry. Each iodine molecule forms two halogen bonds to two adjacent iodide anions (Δ(I···I)=3.2449(7) Å) formally resulting in an almost linear I4 2− anion. The second iodide counter anion is located alternatively beneath and below the H3O+ cation and is not involved in any stronger hydrogen bonding interaction. The dominant feature of the crystal structure of 2 (space group C2/c, a=28.885(5) Å, b=10.6854(15) Å, c=20.659(4) Å, β=110.64(2)°, R gt(F)=0.0776, wR ref(F 2)=0.1410) is a ladder substructure formed by dpmaH cations and neutral dpma molecules via NH···O and NH···N hydrogen bonds. Triiodide counter anions occupy gaps in the ladder. A characteristic Raman signal representing the iodine molecule in the Raman spectrum of 1 is shifted to lower wavenumbers (173 cm−1). It corresponds to an iodine molecule trapped in the cage of a hydrogen bonded network forming medium strong halogen bonds. The Raman spectrum of 2 shows the typical bands of a weakly connected I3 − anion.