Evaluation of N-H...S and N-H...π interactions in O,O'-diethyl N-(2,4,6-trimethylphenyl)thiophosphate: a combination of X-ray crystallographic and theoretical studies

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.

Exploring concomitant/conformational dimorphism in a difluoro-substituted phosphoramidate derivative

The concomitant occurrence of dimorphs of diphenyl (3,4-difluorophenyl)phosphoramidate, C₁₈H₁₄F₂NO₃P, was observed via a solution-mediated crystallization process with variation in the symmetry-free molecules (Z'). The existence of two forms, i.e. Form I (block, Z' = 1) and Form II (needle, Z' = 2), was characterized by single-crystal X-ray diffraction, differential scanning calorimetry and powder X-ray diffraction. Furthermore, a quantitative analysis of the energetics of the different intermolecular interactions was carried out via the energy decomposition method (PIXEL), which corroborates with inputs from the energy framework and looks at the topology of the various intermolecular interactions present in both forms. The unequivocally distinguished contribution of strong N-H...O hydrogen bonds along with other interactions, such as C-H...O, C-H...F, π-π and C-H...π, mapped on the Hirshfeld surface is depicted by two-dimensional fingerprint plots. Apart from the major electrostatic contribution from N-H...O hydrogen bonds, the crystal structures are stabilized by contributions from the dispersion energy. The closely related melting points and opposite trends in the calculated lattice energies are interesting to investigate with respect to the thermodynamic stability of the observed dimorphs. The significant variation in the torsion angles in both forms helps in classifying them in the category of conformational polymorphs.

Dicyclohexylammonium O,O’-Diphenyl Phosphate, [(C6H11)2NH2][(C6H5O)2P(O)(O)]: Spectroscopic Study, Crystal Structure, and Hirshfeld Surface Analysis

The title salt, [(C6H11)2NH2][(C6H5O)2P(O)(O)], crystallizes in the chiral space group P212121, composed of achiral cation and anion components. The strong charge-assisted N–H…O hydrogen bonds build a linear assembly along the a axis, including a non-centrosymmetric C22(6) chain graph-set motif. The intra and intermolecular C–H…O interactions as well as the C–H…π-electron ring interactions also exist in the crystal structure. Fingerprint plots are used for a detailed investigation of intermolecular interactions participating in the crystal packing. The spectroscopic features (IR, 1H NMR, 13C{1H} NMR, 31P{1H} NMR, and mass) are studied.

Two single-enantiomer amidophosphoesters: a database study on the chirality of (O)2P(O)(N)-based structures

The crystal structures of two single-enantiomer amidophosphoesters with an (O)₂P(O)(N) skeleton, i.e. diphenyl [(R)-(+)-α-methylbenzylamido]phosphate, (I), and diphenyl [(S)-(-)-α-methylbenzylamido]phosphate, (II), both C₂₀H₂₀NO₃P, are reported. In both structures, chiral one-dimensional hydrogen-bonded architectures, along [010], are mediated by N-H...OP interactions. The statistically identical assemblies include the noncentrosymmetric graph-set motif C(4) and the compounds crystallize in the chiral space group P2₁. As a result of synergistic co-operation from C-H...O interactions, a two-dimensional superstructure is built including a noncentrosymmetric R₄⁴(22) hydrogen-bonded motif. A Cambridge Structural Database survey was performed on (O)₂P(O)(N)-based structures in order to review the frequency of space groups observed in this family of compounds; the hydrogen-bond motifs in structures with chiral space groups and the types of groups inducing chirality are discussed. The ^2,3J_X-P (X = H or C) coupling constants from the NMR spectra of (I) and (II) have been studied. In each compound, the two diastereotopic C₆H₅O groups are different, which is reflected in the different chemical shifts and some coupling constants.

Decorated single-enantiomer phosphoramide-based silica/magnetic nanocomposites for direct enantioseparation

The nano-composites Fe₃O₄@SiO₂@PTA(+) and Fe₃O₄@SiO₂@PTA(−) (PTA: phosphoric triamide) were prepared and used for the chiral separation of five racemic mixtures.

A combined X-ray crystallography and theoretical study of N-H...OX (X is =P and -C) hydrogen bonds in two new structures with a (C-O)2(N)P(=Y) (Y is O and S) skeleton

The crystal structures of N,N'-(cyclohexane-1,4-diyl)bis(O,O'-diphenylphosphoramide), C₃₀H₃₂N₂O₆P₂ or (C₆H₅O)₂P(O)(1-NH)(C₆H₁₀)(4-NH)P(O)(OC₆H₅)₂, (I), and N,N'-(1,4-phenylene)bis(O,O'-dimethylthiophosphoramide), C₁₀H₁₈N₂O₄P₂S₂ or (CH₃O)₂P(S)(1-NH)(C₆H₄)(4-NH)P(S)(OCH₃)₂, (II), have been investigated. In the structure of (I), with an (O)₂(N)P(O) skeleton, two symmetry-independent phosphoramide molecules are linked through N-H...O=P hydrogen bonds. In the structure of (II), with an (O)₂(N)P(S) skeleton, the ester O atoms take part in N-H...O-C hydrogen bonds as acceptors; the P=S groups do not participate in hydrogen-bonding interactions. The strengths of these hydrogen bonds were evaluated, using quantum chemical calculations with the GAUSSIAN09 software package at the B3LYP/6-311G(d,p) level of theory. For this, LP(O) to σ*(NH) charge transfers were studied, according to the second-order perturbation theory in natural bond orbital (NBO) methodology, for a three-component cluster of hydrogen-bonded molecules for both structures, including all of the independent N-H...O hydrogen bonds observed in the crystal packing. The details of the intermolecular interactions were studied by Hirshfeld surface maps and two-dimensional fingerprint plots.