Investigation of crystal structures, energetics and isostructurality in halogen-substituted phosphoramidates.

A total of 14 compounds, one unsubstituted and 13 halogen-substituted phosphoramidates, have been synthesized from unsubstituted and halogenated (fluoro-, difluoro-, chloro-, bromo-, iodo-substituted) aniline and diphenyl phosphoryl chloride to investigate their molecular assembly in solid-state structures. Amongst them, six groups were formed based on similarities in unit-cell dimensions, space group and molecular assembly of the crystal. The analysis reveals that all the crystal structures contain robust N-H...O hydrogen bonds which are the primary building blocks with ancillary interactions such as C-H...O, C-H...π, C-H...F/Cl/Br/I, F...F, F...π, I...π, Br...π, I...O and Br...O. The role of short and directional C-H...O and C-H...π interactions providing significant stabilization to the densely packed crystalline arrangement is discussed. The contribution of these interactions in stabilizing the crystalline assembly was deduced via computing total interaction energy between dimers and the overall lattice energies using the computer programs Crystal Explorer 17.5 and PIXELC, respectively. Additionally, the occurrence of 3D isostructurality in phosphoradimates and their halogenated analogs was investigated using the XPac program. A comparison of the magnitudes of the torsion angles in the compounds substantiates the role of conformational flexibility in the solid state.