Ethane-1,2-diylbis(methyl-phosphinic acid).

In the title compound, C(4)H(12)O(4)P(2), there are two crystallographically independent half-mol-ecules in the asymmetric unit, both molecules lying on centres of symmetry. Each mol-ecule is connected on both sides to neighbouring mol-ecules via strong O-H⋯O hydrogen bonds. The -POOH groups accept and donate one hydrogen bond in interactions with the neighbouring -POOH group of the adjacent mol-ecule, to give one-dimensional chains along [10]. As each phosphinic acid group donates and accepts one hydrogen bond, the connection between the mol-ecules is best described by a ring motif which can be classified by the Etter symbol R(2) (2)(8).