A novel three-dimensional Cd^II coordination polymer: poly[[aquabis(2,2′-bipyridine)(μ₅-pyrazol-1-ide-3,5-dicarboxyl­ato)(μ₄-pyrazol-1-ide-3,5-dicarboxyl­ato)(μ₃-pyrazole-3,5-dicarboxyl­ato)tetra­cadmium(II)] dihydrate]

The title compound, {[Cd₄(C₅H₂N₂O₄)(C₅HN₂O₄)₂(C₁₀H₈N₂)₂(H₂O)]·2H₂O}_n, crystallized in the monoclinic space group P2₁/n and displays a three-dimensional architecture. The asymmetric unit is composed of four crystallographically independent Cd^II centres, two triply deprotonated pyrazole-3,5-dicarb­oxy­lic acid mol­ecules, one doubly deprotonated pyrazole-3,5-dicarb­oxy­lic acid mol­ecule, two 2,2′-bipyridine ligands, one coordinated water mol­ecule and two inter­stitial water mol­ecules. Inter­estingly, the Cd^II centers exhibit two different coordination numbers. Two Cd^II centres adopt a distorted octa­hedral arrangement and a third a trigonal–prismatic geometry, though they are all hexa­coordinated. However, the fourth Cd^II center is hepta­coordinated and displays a penta­gonal–bipyramidal geometry. The three anionic ligands adopt μ₃-, μ₄- and μ₅-bridging modes, first linking Cd^II centers into a one-dimensional wave-like band, then into a wave-like layer and finally into a three-dimensional coordination framework, which is stabilized by hydrogen bonds.