Poly[aqua[μ3-(pyridin-1-ium-3,5-diyl)diphosphonato-κ3O:O':O''][μ2-(pyridin-1-ium-3,5-diyl)diphosphonato-κ2O:O']calcium(II)].

The rigid organic ligand (pyridine-3,5-diyl)diphosphonic acid has been used to create the title novel three-dimensional coordination polymer, Ca(C(5)H(6)NO(6)P(2))(2)(H(2)O). The six-coordinate calcium ion is in a distorted octahedral environment, formed by five phosphonate O atoms from five different (pyridin-1-ium-3,5-diyl)diphosphonate ligands, two of which are unique, and one water O atom. Two crystallographically independent acid monoanions, L1 and L2, serve to link metal centres using two different coordination modes, viz. η(2)μ(2) and η(3)μ(3), respectively. The latter ligand, L2, forms a strongly undulated two-dimensional framework parallel to the crystallographic bc plane, whereas the former ligand, L1, is utilized in the formation of one-dimensional helical chains in the [010] direction. The two sublattices of L1 and L2 interweave at the Ca(2+) ions to form a three-dimensional framework. In addition, multiple O-H···O and N-H···O hydrogen bonds stabilize the three-dimensional coordination network. Topologically, the three-dimensional framework can be simplified as a very unusual (2,3,5)-connected three-nodal net represented by the Schläfli symbol (4·8(2))(4·8(8)·10)(8).