N-H···O and N-H···N interactions in three pyran derivatives.

The three pyran structures 6-methylamino-5-nitro-2,4-diphenyl-4H-pyran-3-carbonitrile, C19H15N3O3, (I), 4-(3-fluorophenyl)-6-methylamino-5-nitro-2-phenyl-4H-pyran-3-carbonitrile, C19H14FN3O3, (II), and 4-(4-chlorophenyl)-6-methylamino-5-nitro-2-phenyl-4H-pyran-3-carbonitrile, C19H14ClN3O3, (III), differ in the nature of the aryl group at the 4-position. The heterocyclic ring in all three structures adopts a flattened boat conformation. The dihedral angle between the pseudo-axial phenyl substituent and the flat part of the pyran ring is 89.97 (1)° in (I), 80.11 (1)° in (II) and 87.77 (1)° in (III). In all three crystal structures, a strong intramolecular N-H···O hydrogen bond links the flat conjugated H-N-C=C-N-O fragment into a six-membered ring. In (II), molecules are linked into dimeric aggregates by N-H··· O(nitro) hydrogen bonds, generating an R2(2)(12) graph-set motif. In (III), intermolecular N-H···N and C-H···N hydrogen bonds link the molecules into a linear chain pattern generating C(8) and C(9) graph-set motifs, respectively.