Combination of X-ray crystallography and theoretical study to evaluate the effect of NH⋯OP versus NH⋯OC hydrogen bonds on the NH stretching frequencies

► The hydrogen-bonded clusters were calculated. ► The experimental hydrogen bond pattern is a starting point for calculation. ► The influence of stronger P(O)⋯HNC(O)NHP(O) hydrogen bond was compared to the weaker C(O)⋯HNamide. ► The orientation of PO versus CO is gauche.