Synthesis and crystal structure of a 6-chloro­nicotinate salt of a one-dimensional cationic nickel(II) coordination polymer with 4,4′-bi­pyridine

A 6-chloro­nicotinate (6-Clnic) salt of a one-dimensional cationic nickel(II) coordination polymer with 4,4′-bi­pyridine (4,4′-bpy), namely, catena-poly[[tetra­aqua­nickel(II)]-μ-4,4′-bi­pyridine-κ2N:N′] bis­(6-chloro­nicotinate) tetra­hydrate], {[Ni(C10H8N2)(H2O)4](C6H3ClNO2)2·4H2O}n or {[Ni(4,4′-bpy)(H2O)4](6-Clnic)2·4H2O}n, (1), was prepared by the reaction of nickel(II) sulfate hepta­hydrate, 6-chloro­nicotinic acid and 4,4′-bi­pyridine in a mixture of water and ethanol. The mol­ecular structure of 1 comprises a one-dimensional polymeric {[Ni(4,4′-bpy)(H2O)4]2+}n cation, two 6-chloro­nicotinate anions and four water mol­ecules of crystallization per repeating polymeric unit. The nickel(II) ion in the polymeric cation is octa­hedrally coordinated by four water mol­ecule O atoms and by two 4,4′-bi­pyridine N atoms in the trans position. The 4,4′-bi­pyridine ligands act as bridges and, thus, connect the symmetry-related nickel(II) ions into an infinite one-dimensional polymeric chain extending along the b-axis direction. In the extended structure of 1, the polymeric chains of {[Ni(4,4′-bpy)(H2O)4]2+}n, the 6-chloro­nicotinate anions and the water mol­ecules of crystallization are assembled into an infinite three-dimensional hydrogen-bonded network via strong O—H⋯O and O—H⋯N hydrogen bonds, leading to the formation of the representative hydrogen-bonded ring motifs: tetra­meric R24(8) and R44(10) loops, a dimeric R22(8) loop and a penta­meric R45(16) loop.