Two iodine-rich (dimethylphosphoryl)methanaminium iodides

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 ( dpma H) 3 (H 3 O)I 4 · 1 / 2 I 2 ( 1 ) as the main product and a small amount of a by-product ( dpma H) 2 [I 3 ] 2 · dpma ( 2 ). Single crystal structure determinations on both compounds were carried out. In the crystal structure of 1 (space group P 3̅, a =12.2166(3) Å, c =10.8788(4) Å, R gt ( F )= 0.0224, wR ref ( F 2 )=0.0377), six symmetry related dpma H + 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 H 3 O + 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 I 2 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 I 4 2− anion. The second iodide counter anion is located alternatively beneath and below the H 3 O + cation and is not involved in any stronger hydrogen bonding interaction. The dominant feature of the crystal structure of 2 (space group C 2/ 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 dpma H 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 I 3 − anion.