Structural studies on two new phosphoramides with the same [OC4H8N]P(O) segment by means of single-crystal X-ray diffraction, Hirshfeld surface analysis and 3D energy framework approach

Abstract

Two new phosphoramides containing the same [OC4H8N]P(O) segment (bearing the substituent morpholine) accompanied by different [C(O)NH]P(O)[N]2 (phosphoric triamide, 1) and [N]P(O)[O]2 (amidophosphoric acid ester, 2) skeletons are investigated by single crystal X-ray diffraction and completed by FT-IR and 1H, 13C, 31P NMR spectroscopy. Structures 1 and 2 crystallize in the triclinic space group P1¯ and the monoclinic space group I2/a, respectively, both with one independent molecule in the asymmetric unit. The crystal structure of 1 is stabilized via a classical hydrogen bond interaction N—H…OP as a dimer pattern extending into a 3D network by non-classical C—H…F, C—H…Cl and C—H…O weak hydrogen bond interactions, while, the crystal packing of 2 is mostly dominated by the non-classical hydrogen bond interaction (C―H…)3OP. A precise exploration of the intermolecular interactions by using different analysis tools including three-dimensional (3D) Hirshfeld surfaces, 2D fingerprint plots, enrichment ratios, and 3D energy frameworks shows that the attractive X―H…OP (X = N or C) hydrogen bond interactions on the Hirshfeld surfaces are quite enriched and thus accepted as favoured contacts. Based on the interaction energy analysis, a dominant electrostatic nature is found for the classical hydrogen bond interaction N―H…OP in 1, while the non-classical (C―H…)3OP hydrogen bond interaction in 2 shows both electrostatic and dispersion components. Furthermore, an interesting outcome of the obtained results is that the stability of both phosphoramide structures, in the presence (for 1) or absence (for 2) of a classical (strong) interaction, is given by pseudo-similar intermolecular connectivities with the contribution of the PO group as an suitable H atom acceptor site.