Synthesis and crystal structure of a 6-chloro-nicotinate salt of a one-dimensional cationic nickel(II) coordination polymer with 4,4'-bi-pyridine

Abstract

A 6-chloro-nicotinate (6-Clnic) salt of a one-dimensional cationic nickel(II) coordination polymer with 4,4'-bi-pyridine (4,4'-bpy), namely, catena-poly[[[tetra-aqua-nickel(II)]-μ-4,4'-bi-pyridine-κ² N:N'] bis-(6-chloro-nicotinate) tetra-hydrate], {[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 hepta-hydrate, 6-chloro-nicotinic acid and 4,4'-bi-pyridine in a mixture of water and ethanol. The mol-ecular structure of 1 comprises a one-dimensional polymeric {[Ni(4,4'-bpy)(H₂O)₄]²⁺} _n cation, two 6-chloro-nicotinate anions and four water mol-ecules of crystallization per repeating polymeric unit. The nickel(II) ion in the polymeric cation is octa-hedrally coordinated by four water mol-ecule O atoms and by two 4,4'-bi-pyridine N atoms in the trans position. The 4,4'-bi-pyridine 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-chloro-nicotinate anions and the water mol-ecules 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: tetra-meric R ² ₄(8) and R ⁴ ₄(10) loops, a dimeric R ² ₂(8) loop and a penta-meric R ⁴ ₅(16) loop.

Keywords: 4,4′-bi­pyridine; 6-chloro­nicotinic acid; coordination polymer; crystal structure; hydrogen-bond motif; nickel(II).