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 center dot center dot center dot O interactions between the phosphonic acid sites. Weak C-H center dot center dot center dot pi interactions are established in the aromatic regions.