Hydrogen-bonded network in biphenyl-4,4′-diphospho­nic acid

The crystal structure of the title compound, C₁₂H₁₂O₆P₂, displays two different regions alternating along the a axis: a hydrogen-bonded region encompassing the end-positioned phospho­nic acid groups and a hydro­phobic region formed by the aromatic spacers. The asymmetric unit contains only half of the biphenyl-4,4′-diphospho­nic acid (4,4′-bpdp) mol­ecule, which is symmetric with an inversion centre imposed at the mid-point between the two aromatic rings. The periodic organization of the mol­ecules is controlled by two strong O—H...O inter­actions between the phospho­nic acid sites. Weak C—H...π inter­actions are established in the aromatic regions.