Poly[diaqua-(µ(2)-oxalato-κO,O:O,O)(µ(2)-pyrazine-2-carboxyl-ato-κN,O:O,O')neodymium(III)].

In the title complex, [Nd(C(5)H(3)N(2)O(2))(C(2)O(4))(H(2)O)(2)](n), the Nd(III) atom is ten-coordinated by one N atom and three O atoms from two pyrazine-2-carboxyl-ate ligands, four O atoms from two oxalate ligands and two water mol-ecules in a distorted bicapped square-anti-prismatic geometry. The two crystallographically independent oxalate ligands, each lying on an inversion center, act as bridging ligands, linking Nd atoms into an extended zigzag chain. Neighboring chains are linked by the pyrazine-2-carboxyl-ate ligands into a two-dimensional layerlike network in the (10) plane. The layers are further connected by O-H⋯O and O-H⋯N hydrogen bonds, forming a three-dimensional supra-molecular network.

4-(4-Pyrid-yl)pyridinium 3',4,4'-tricarboxy-biphenyl-3-carboxyl-ate dihydrate.

In the title compound, C(10)H(9)N(2) (+)·C(16)H(9)O(8) (-)·2H(2)O, both the cation and anion possess crystallographically imposed centres of symmetry, causing the nitro-gen-bound H atom in the 4-(4-pyrid-yl)pyridinium cation and the acidic H atom of the carboxyl-ate groups at the 3 and 3' positions in the anion to be disordered over two positions with equal occupancies. In the crystal packing, the cations, anions and water mol-ecules are connected by O-H⋯O, C-H⋯O and N-H⋯N hydrogen bonds, forming layers parallel to (20). These layer are further connected into a three-dimensional supra-molecular network by O-H⋯O hydrogen bonds involving the water mol-ecules as H-atom donors and by weak π-π stacking inter-actions between neighbouring benzene and pyridine rings, with centroid-centroid distances of 3.756 (5) Å.