(R)-Methyl {[(2-carb­oxy­bicyclo­[2.2.2]octan-1-yl)­ammonio]­methyl}­phos­phon­ate dichloro­methane 0.25-solvate

The carb­oxy­lic acid mol­ecule of the title compound, C(11)H(20)NO(5)P·0.25CH(2)Cl(2), exists as a zwitterion with the H atom of the phospho­nate group being transferred to the imine N atom. In the asymmetric unit, there are two crystallographically independent acid mol­ecules adopting the same absolute configuration and differing slightly in their geometrical parameters. In each mol­ecule, the imino and carboxyl groups are connected via an intra­molecular N—H⋯O hydrogen bond. Inter­molecular O—H⋯O and N—H⋯O hydrogen bonds induce the formation of layers parallel to the ab plane. The dichloro­methane solvent mol­ecule, with a site occupancy of 0.5, is located between the layers.