Crystal structure of catena-poly[[[triaqua(4-cyanobenzoato-κO)nickel(II)]-μ-4,4′-bipyridine-κ2 N:N′] 4-cyanobenzoate]

In the title polymeric complex salt, {[Ni(C8H4NO2)(C10H8N2)(H2O)3](C8H4NO2)}n, the NiII cation is coordinated by a 4-cyanobenzoate anion, two 4,4′-bipyridine ligands and three water molecules in a distorted N2O4 octahedral geometry. The 4,4′-bipyridine ligands bridge the NiII cations to form polymeric chains of the title complex cations, propagating along the c-axis direction. The dihedral angle between the pyridine rings of the 4,4′-bipyridine ligand is 24.9 (6)°. In the crystal, the uncoordinating 4-cyanobenzoate anions link with the complex cations via O—H⋯O hydrogen bonds into a three-dimensional supramolecular architecture. Weak C—H⋯O, C—H⋯N interactions and π–π stacking [centroid-to-centroid distances = 3.566 (4) and 3.885 (4) Å] are also observed in the crystal.


S1. Comment
The design of metal-organic frameworks is of current interest in the fields of supramolecular chemistry and crystal engineering. This interest stems from their potential applications as functional materials, such as in gas storage, ionexchange, catalysis, magnetism and molecular sensing (Peña-Rodríguez et al., 2014;Song et al. 2009). In the field of crystal engineering, 4,4′-bipyridine has been extensively used to construct novel one-, two-, and three dimensional coordination polymers with potential applications as functional materials. The combination of 4,4′-bipyridine and carboxylic acid is largely directed toward interesting topologies (Biradha et al. 1999). 4-cyanobenzoic acid has been used to develop fluorescent materials (He & Zhu 2003a,b). 4,4′-Bipyridine is an excellent, rigid bridging ligand for the construction of novel metal-organic frameworks due to its various coordinative modes with metal ions. Currently all the metal-organic coordination compounds obtained with cyanobenzoic acid and 4,4′-bipyridine contain the cyanobenzoato group as mono-or bidentate ligand, the title compound is the first example of a polymeric structure with cyanobenzoate as a counter ion.
The title compound is a nickel(II) polymeric complex cation ( In the crystal, the uncoordinate 4-cyanobenzoate anions link with the complex cations via O-H···O hydrogen bonds into the three dimensional supramolecular architecture. Weak C-H···O, C-H···N and π-π stacking [centroid-to-centroid distances = 3.566 (4) and 3.885 (4) Å] are also observed in the crystal.

S2. Experimental
A solution of nickel(II) nitrate hexahydrate (62.1 mg, 0.21 mmol) in 5 mL of deionized water was added dropwise to 5 mL of a methanol solution of 4,4′-bipyridine (50 mg, 0.32 mmol), the reaction mixture was refluxed for two hours; after which a solution of 4-cyanobenzoic acid (62.8 mg, 0.42 mmol) in 5 mL of DMF was slowly added at room temperature, the reaction mixture was refluxed for five hours. The solid was crystallized from the solution giving blue crystals of the title compound which were suitable for X-ray crystal structure analysis and fully characterized by standard analytical

S3. Refinement
The water H atoms were located in a difference Fourier map and refined with a distance restraint O-H = 0.84 Å, U iso (H) = 1.2U eq (O). Other H atoms were positioned geometrically and refined using a riding model approximation with distance C-H = 0.93 Å, U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure of the title compound, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level, H atoms are omitted for clarity.

catena-Poly[[[triaqua(4-cyanobenzoato-κO)nickel(II)]-µ-4,4′-bipyridine-κ 2 N:N′] 4-cyanobenzoate]
Crystal data [Ni(C 8  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.38 e Å −3 Δρ min = −0.38 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.