Competing and directing interactions in new phosphoramide/thiophosphoramide structures: energy considerations and evidence for CH⋯HC contacts and aliphatic–aromatic stacking

Abstract

Supramolecular aggregates, driven by different molecular functionalities and crystal forces, are studied in new phosphoramide and thiophosphoramide structures (C₆H₅O)₂P(O)(2-NHC₅H₄N) (I), (4-Cl–C₆H₄O)P(O)(NHC₆H₁₁)₂ (II), (4-Cl–C₆H₄O)P(O)(N(CH₃)C₆H₁₁)₂ (III), P(S)(NHC(CH₃)₃)₃ (IV), and P(S)(3-NHC₅H₄N)₃ (V). DH⋯A (D = N, C; A = N, O, S) hydrogen bonds, contacts related to the ring stacking (CH⋯π/σ⋯π and π⋯π) and some other weak interactions are the structural elements inspected. The techniques/methods used are X-ray crystallography, QTAIM, NCI, 2D fingerprint plots, and lattice energy calculations, complemented by spectroscopic approaches for some additional investigations. A comparison is made with selected analogous structures from the Cambridge Structural Database (CSD). Determinative roles of stronger hydrogen bonds and competition between weaker hydrogen bonds (mostly having dispersion characteristics) are addressed as well as the cyclohexyl⋯arene (σ⋯π) stacking with pronounced CH⋯π interactions. When the strength and specificity of the hydrogen bonds decrease, the molecules can form a denser packing, and the role of CH⋯HC interactions becomes prominent. Despite their weakness, such interactions together make the bulk of the crystal stabilizing forces.