Supramolecular architecture in azaheterocyclic phosphonates. III. Structures of an ethyl phosphonamidate and an ethyl phosphonate.

The novel crystal structures of ethyl (S)-P-(4-oxo-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-3-yl)-N-[(R)-1-phenylethyl]phosphonamidate, C20H20N3O3PS, I, and diethyl (4-isopropyl-2-oxo-3,4-dihydro-2H-benzo[4,5]thiazolo[3,2-a]pyrimidin-3-yl)phosphonate, C18H25N2O4PS, II, were characterized by X-ray diffraction analysis. The crystal packing of I is dominated by two infinite stacks composed of symmetry-independent molecules linked by distinctively different hydrogen-bond systems. The structure of II shows a ladder packing topology similar to those observed in related phosphorylated azaheterocycles. Structural studies are supplemented by calculations on the interactions stabilizing the molecular assemblies using the PIXEL method. Additionally, fingerprint plots derived from the Hirshfeld surfaces were generated for each structure to characterize the crystal packing arrangements in detail. The aromaticities of the heterocyclic moieties have been investigated using HOMA and HOMHED parametrization and compared with structures reported previously.