3-Carboxybenzylphosphonic acid (H3L) (1), three complexes [Ca(H2L)2(H2O)3]n (2), [Ca(H2L)2(H2O)2]n (3) and [Ca(H2L)2(H2O)4] bipy (4) and two polymorphs of the salt (bipyH2)(H2L)2 (5, 6), were prepared and their structures were determined by single crystal X-ray diffraction analysis. Compounds 2 and 3 are polymeric species whereas 4 is a mononuclear complex. The calcium ion in 2, 3 and 4 is coordinated by monodeprotonated phosphonic groups (–PO3H−) and water molecules, the carboxylic group remains in the protonated form. The polymer chains or monomeric units are linked together by hydrogen bonds and ionic forces in the case of salts to afford three-dimensional layered supramolecular structures. Also the π⋯π stacking interactions in compounds 4, 5 and 6 contribute to the stabilization of the structures.
