N,N′,N′′‐Tris(p‐methoxy­phenyl)­phospho­ric triamide

The title compound, C₂₁H₂₄N₃O₄P, is a self‐complementary hydrogen‐bond (HB) building unit, with (P=)O as the primary HB acceptor and N—H as the HB donor. Each of the four crystallographically distinct and nearly parallel mol­ecules of the unit cell has a net dipole moment along the P=O bond direction and all of the dipoles are directed in the same general crystallographic direction. Head‐to‐tail N—H⋯O=P double‐HB strands stack adjacent mol­ecules into one‐dimensional infinite polar columns. Each polar column is a 2₁ helix and all columns are essentially parallel, resulting in polar order throughout the entire crystal.