Résumé
Abstract Structural and packing features of three new amidophosphoric acid esters having a common part X P(O)[OCH 2 C(CH 3 ) 2 CH 2 O], with X = [(CH 3 ) 3 CNH] ( 1 ), [(CH 3 ) 2 HCNH] ( 2 ) and [C 6 H 11 (CH 3 )N] ( 3 ), are investigated by single crystal X-ray diffraction. The results illustrate that the compounds 1 and 3 crystallize with one independent molecule in the asymmetric unit; whereas, for 2 , the compound crystallizes with three independent molecules in the asymmetric unit. The crystal structures are mostly stabilized via tri-furcated hydrogen bond interactions (C–H · · ·) 2 (N–H · · ·)O=P in 1 and (C–H · · ·) 3 O=P in 3 , while the stability is given by bi-furcated hydrogen bond interactions (C–H · · ·)(N–H · · ·)O=P in 2 . For a better understanding of the nature, strength and energetics associated with the formation of the quoted multi-center hydrogen bond interactions, the Natural Bond Order (NBO) method from Density Functional Theory (DFT) and a topological analysis by means of Atoms In Molecules (AIM) and Hirshfeld surface procedures were performed. These studies reveal that the studied multi-center hydrogen bond interactions of the type O · · · H are favoured in the crystal packing displaying enrichment ratios larger than unity. The detailed nature of the different interactions in these multi-center interactions is studied for the first time in such compounds. It is shown that the N–H · · · O interaction is rather non-covalent closed-shell whereas the C–H · · · O interaction is more van der Waals closed-shell. Stronger hydrogen bond interactions are observed for a lower multiple H-atom acceptor oxygen in three-center hydrogen bond interactions (C–H · · ·)(N–H · · ·)O=P of 2 than for four-center interactions in 1 [i.e. (C–H · · ·) 2 (N–H · · ·)O=P] and 3 [i.e. (C–H · · ·) 3 O=P]. The better H-atom acceptability of the O atom of P=O compared with the esteric O atom is explained by the richer s -character of the hybrid orbital of the O atom acceptor of P=O coupled with enhance of the polarization and charge. The obtained results are also confirmed by Molecular Electrostatic Potential (MEP).