A novel three-dimensional CdII 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, {[Cd(4)(C(5)H(2)N(2)O(4))(C(5)HN(2)O(4))(2)(C(10)H(8)N(2))(2)(H(2)O)]·2H(2)O}(n), crystallized in the monoclinic space group P2(1)/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 μ(3)-, μ(4)- and μ(5)-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.