Bis(3,5-dimeth-oxy-phen-yl)phosphinic acid.

In the crystal structure of the title compound, C(16)H(19)O(6)P, inter-molecular O-H⋯O inter-actions link the mol-ecules into chains parallel to the b axis. These chains are linked by C-H⋯π and π-π inter-actions [centroid-centroid distance = 3.7307†(29)†à ] into a three-dimensional network. The dihedral angle between the benzene rings is 73.5†(1)°. The C and O atoms of all four methoxy groups lie very close to the mean planes of their attached rings; the C atoms are 0.055†(2)-0.1038†(1)†à out of the mean plane of the attached rings.