Two new phosphoramidates with formula C 6 H 5 OP(O)(NHC 6 H 11 ) 2 (1) and [N(CH 3 )(C 6 H 11 )]P(O)(2-C 5 H 4 N-NH) 2 (2) were synthesized and characterized by 1 H, 13 C, 31 P NMR and IR spectroscopies and elemental analyses. The crystal structures of these compounds were determined using X-ray crystallography. Compound 1 [triclinic, P1¯, a=8.8679(16)Å, b=10.230(2)Å, c=12.511(2)Å, α=95.918(4)°, β=103.948(4)°, γ=110.818(4)°, Z=2] forms a centrosymmetric dimmer via two equal intermolecular PO⋯HN hydrogen bonds. In this structure, intermolecular hydrogen bonds are also formed between the crystallization solvent and phosphoramidate molecules. Compound 2 [monoclinic, P2 1 /c, a=11.4760(7)Å, b=18.5607(12)Å, c=8.6227(6)Å, β=108.751(5)°, Z=4] produces a one-dimensional polymeric chain through intermolecular PO⋯HN hydrogen bonds, and a weaker intramolecular N⋯HN hydrogen bond has been also observed in the crystal. Ab initio quantum chemical calculations were performed for molecules 1 and 2 by the density functional three-parameter hybrid (DFT/B3LYP) and the Hartree–Fock (HF) methods, using the 6-31G ∗ basis set. The compound 1:CH 3 OH pair was also calculated as observed in the crystal. The computed geometrical parameters are in good agreement with the experimental results.